A simulation tool for better management of retinal services

Eren Demir
David Southern
Aimee Verner
Winfried Amoaku
A simulation tool for better management of retinal services
10.1186/s12913-018-3560-5R E S E A R C H A R T I C L E Open Access
Background: Advances in the management of retinal diseases have been fast-paced as new treatments become available, resulting in increasing numbers of patients receiving treatment in hospital retinal services. These patients require frequent and long-term follow-up and repeated treatments, resulting in increased pressure on clinical workloads. Due to limited clinic capacity, many National Health Service (NHS) clinics are failing to maintain recommended follow-up intervals for patients receiving care. As such, clear and robust, long term retinal service models are required to assess and respond to the needs of local populations, both currently and in the future.Methods: A discrete event simulation (DES) tool was developed to facilitate the improvement of retinal services by identifying efficiencies and cost savings within the pathway of care. For a mid-size hospital in England serving a population of over 500,000, we used 36 months of patient level data in conjunction with statistical forecasting and simulation to predict the impact of making changes within the service. Results: A simulation of increased demand and a potential solution of the 'Treat and Extend' (T&E) regimen which is reported to result in better outcomes, in combination with virtual clinics which improve quality, effectiveness and productivity and thus increase capacity is presented. Without the virtual clinic, where T&E is implemented along with the current service, we notice a sharp increase in the number of follow-ups, number of Anti-VEGF injections, and utilisation of resources. In the case of combining T&E with virtual clinics, there is a negligible (almost 0%) impact on utilisation of resources.Conclusions: Expansion of services to accommodate increasing number of patients seen and treated in retinal services is feasible with service re-organisation. It is inevitable that some form of initial investment is required to implement service expansion through T&E and virtual clinics. However, modelling with DES indicates that such investment is outweighed by cost reductions in the long term as more patients receive optimal treatment and retain vision with better outcomes. The model also shows that the service will experience an average of 10% increase in surplus capacity.

Background

Hospital Eye Services in the United Kingdom (UK) National Health Service (NHS) have consistently had a low profile, despite providing a high volume of work. They account for nearly one in ten hospital outpatient appointments, as the second highest demand specialty with 5.95 million clinic attendances in 2009/10 in England and 7-8% of all surgical operations performed by the NHS. Furthermore, demand has risen by 25% over 7 years [1].

Amongst all ophthalmology clinic attendances, retinal vascular diseases are a leading cause of sight loss. The three specific causes of such visual loss are age related macular degeneration (AMD), diabetic retinopathy (DR), and retinal vascular occlusions (RVO). These conditions are of particular interest as their prevalence is rising in an increasingly ageing population, as AMD and RVO are associated with increasing age, and diabetes mellitus, occurs more frequently. AMD as a serious macular disorder, which is forecasted to rise from 513,000 in 2010 to 679,000 in 2020, an increase of 32% in just 10 years [2]. These patients may require monthly outpatient visits and treatments until disease stability is achieved, followed by implementation of various regimens including pro re nata (PRN) treatment, fixed interval dosing being the most popular until recently [3][4][5][6]. Emerging evidence suggests that outcomes are better with Treat and Extend (T&E) regimen [7][8][9][10][11]. However, these treatments and regimen are resource intensive, and require multi-disciplinary teams including photographers, optometrists, specialist nurses, and pharmacists, in addition to the ophthalmologist.

Given the frequency of treatment and monitoring visits (usually monthly), combined with increasing demand for services where the number of treatable patients potentially suitable for treatment have risen markedly, many NHS ophthalmology clinics are currently running at 100% capacity and some are failing to maintain the recommended follow-up and re-treatment intervals. Most of these clinics which are running at maximum capacity may not have scope for further expansion. They cannot cope with the current patient numbers, let alone allow for future increases in patient numbers.

It is clear that robust and long term retinal service delivery modelling is required across NHS clinics in order to determine the current and future needs of local populations, so that there is no future compromise in the standard of service provision, including follow-up (FU) intervals and quality of intravitreal treatment administration. Amoaku et al. (2012) [12] produced a comprehensive list of changes that can be made in order to meet existing demand and needs of patients with limited resources and capacity. In that publication, the authors shared a number of service re-design case studies, e.g., virtual clinics. Virtual clinics usually consist of non-mydriatic photos of the optic disc, visual fields, and visual acuity measurements carried out by a technician, stored, and later reviewed by an Ophthalmologist [13]. A virtual clinic can be within a hospital setting or in a location within the community. If it is located in the community then patients are shifted from a hospital setting where treatment (or a follow-up routine appointment) is provided out in the community, thus releasing the pressure on hospitals. A number of other authors have presented similar models (including virtual clinics) of dealing with capacity constraints [14][15][16][17][18].

Despite these efforts, the quantifiable impact of re-designing retinal services has never been studied. Whether planned service re-design will actually result in increased capacity, and if so how much cost improvement will result remains unknown. Furthermore, it is unknown as to how a change in one area of the service will impact on resources in another including activity (new and FU appointments), resource utilisation and costing and revenue.

The aims of this study are therefore: 1) to develop a discrete event simulation (DES) model, which captures the retinal service treatment pathways and service re-designs including virtual clinics; 2) Second, to determine possible and realistic policies, which could be implemented with regard to an increased use of virtual clinics combined with a new treatment regimen (known as treat and extend), and how these would affect hospital based treatment; 3) to evaluate the impact of the implementation of this service re-design on a number of operational and cost performance indicators relevant to the delivery of retinal services. This should provide an indication of the feasibility and scale of improvement, both operationally and patient outcomes, and allow health managers to make informed decisions with regard to the best ways to reconfigure the delivery of retinal services in the UK. This study was based on the retinal service of a mid-sized NHS hospital Trust in England.

Methods

A unique version of a discrete event simulation model was developed for Cambridge University Hospitals NHS Foundation Trust in three stages. Firstly, the Trust's patient level ophthalmology data was anonymised and analysed in greater detail. Secondly, the structure of the Trust's intravitreal injection service as delivered at the time (mainly a prn regime) was established using management and clinician expertise. Finally, the combination of both sets of analysis and statistical forecasts were entered into the model. Using sophisticated statistical algorithms, we forecast activity by patient type (AMD, DR and RVO) broken down by new patients and follow-up (FU) visits. The simulation was then ran many times giving accurate information on the next twelve months of activity, resource utilisation and revenue/costing to provide baseline values. The baseline was then compared to any number of other alternative methods of delivering the intravitreal injection service. This enabled the Trust to explore the impact of service redesign options rapidly and with ease in order to identify the most effective solutions.

The problem/hypothesis

In order to address the issue of increasing patient numbers and to demonstrate how the model could be used to identify service efficiencies, we explored the impact on the service by adopting the T&E regimen in combination with virtual clinics compared to the current regime of prn delivery as described in the SUSTAIN Study [4,[7][8][9][10]18]. Using real data from this hospital Trust, it was confirmed that the service currently used the PRN regime. The model calculated that there was an average rate of 4 injections in year 1, 3 in year 2, and 2.5 in year 3 with this regime. The service would like to change their treatment methodology to T&E in order to improve patient outcomes. However, this would mean an increase in the number of injections to 8, 6 and 4-5 in years 1, 2 and 3, respectively. Analysis of the service data indicated that there was insufficient capacity to increase the number of injections at neutral cost without other service changes. The adoption of virtual clinics seemed to have the impact of reducing the number of FU appointments at the Trust.

Conceptualising retinal service patient pathway

The objective was to explore the clinic pathway in retinal services in order to establish what, in the experts' opinion, were important areas for development. The pathway mapping consisted of structured interviews with retinal service nurses across a number of clinics between March and August 2015. The interviewer discussed each stage of the pathway with the interviewee taking account of the interviewee's opinion and adjusting the pathway in 'real time' as comments were made.

According to the interviews, the typical care system in place in the NHS and elsewhere, for the diagnosis, initial treatment and subsequent FU/treatments in patients with eye problems comprised of a complex set of services offered in and out of hospital. Fig. 1 shows the inner workings of the retinal service pathway diagrammatically. Patients were referred (first referral) to retinal services via their General Practitioner (GP) or community optometrist and, on a small number of occasions, via accident and emergency (A&E) or outpatient services. FU evaluation and treatment would subsequently follow. Existing patients will either continue treatment (primarily with intravitreal injections) and/or continue with monitoring/assessment (follow-up review) as described in SUSTAIN study [4]. To facilitate real life setting, the Trust's appointment booking system was incorporated into the model to ensure bookings were captured accordingly. Where a patient either cancelled or 'did not attend' (DNA) re-bookings were made according to the service rules.

Patient level data analysis and forecasting

Thirty-six months of individual patient level data was obtained from Cambridge University Hospitals NHS Trust (April 2013 -March 2016). Using the statistical software R (library package forecast), a series of models was developed to forecast activity by patient type (nAMD, DR and RVO) broken down into "new patients" and "FUs". The forecasted activity was then adjusted for population growth rates and collated to estimate future activity for 2016-17 (12 months forecast). When the projected activity for 2015-16 was compared with the actual activity, forecast accuracy was in the region of 90-99%.

In addition to demand forecasting, many parameters were estimated and their distributions were identified by using the fitdistr package in R, such as the distribution  of the number of injections in years 1, 2 and 3 of treatment, waiting time for the first outpatient appointment, distribution of the number of FU assessments in each of the 3 years. Individual patients were tracked over the 36 month period and the number of times the patient was injected and monitored was counted within each of the 3 years.

Model input parameters

Model inputs included staffing levels and salaries, staff availability, staff responsibilities, treatment pathways, arrivals (forecasted activity by new vs. follow-up attendances), percentage of patients falling into each category (nAMD, DR and RVO), costing of each service/drug/ staff, treatment option visit parameters, appointment booking system parameters, clinician rota system, room/ injection bed availability and weekly clinic sessions. The majority of input parameters were estimated through exhaustive analysis of patient level data, and where no data was available literature and/or expert opinion was used. See Additional file 1: Table S5 for the list of input parameters.

Service re-design

Service delivery configurations involving increased use of community services (e.g. virtual clinics) could yield efficiency gains both operationally and financially. Operationally, it reduces unnecessary hospital attendances to ophthalmology clinics, and the need for consultations with ophthalmology doctors and nurses. Financially, treating patients in the community (i.e. within a virtual clinic setting) has a significant cost advantage over treatment in hospitals. The average cost of an outpatient follow-up assessment (or routine check-up) is around £89, whereas the same visit within a virtual clinic would cost in the region of £30-£45 [19]. This is why increased use of virtual clinics are welcomed by the Department of Health and Social Care in England, and in-line with their current policies. Virtual clinics are also welcomed by key decision makers within ophthalmology clinics, including service managers, consultants and senior nurses. It relieves the pressure for patient's waiting for an outpatient appointment (first referral) and existing patients to receive frequency of treatment as recommended by the National Institute for Health and Care Excellence (NICE) [20]. The vast majority of research with regard to ophthalmology clinic operations and performance evaluation, has focused on quality of life of patients and the effects of AMD, DR and RVO related symptoms and social factors on the physical and psychological wellbeing of patients. The lack of research to evaluate operational and cost performance of possible service re-designs within retinal services warrants further investigation. The discrete event simulation model we have developed here enables us to experiment any combination of service re-design configurations, i.e., the model is generic enough to run any set of scenarios.

Amongst many service configurations virtual clinic is known to be the most popular form of service re-design, which was also requested by ophthalmology (retinal service) managers, doctors and senior nurses. In addition to virtual clinics we also experiment the system under a new treatment regime. Therefore, in order to change from the existing service utilisation of the PRN to a T&E regime to improve patient outcomes, an increase in the number of injections to 8, 6 and 5 in years 1, 2 and 3, respectively would be required. Analysis of the service data showed clearly that at the time there was insufficient capacity to increase the number of injections. Projections were made as to how many appointment slots were required in order to bridge the capacity shortfall. The impact such a service change on activity, resource utilisation, costing and revenue required determination.

Results

According to the patient level data the Trust had a total of 6520 attending patients, including 17.2%, 42.3% and 40.5% are nAMD, DR and other medical retina (MR) conditions (including 50% RVO patients, and the remaining 50% which were non-AMD/DR/RVO related), respectively.

Over the 3 year period of April 2013 -March 2016, a total of 22,129 appointments were attended, of which 42% were nAMD related (9354), 32% DR (6977) and 26% other MRE diseases including RVO (5798) (see Table 1).

The 3295 injections for nAMD patients incurred 4851 FU assessments and a further 1208 assessments for patients who had no form of treatment (observation only). Approximately 69% and 66% of activity for DR and MR respectively were observation/monitoring only, and did not require any intravitreal injections. Table 2 shows the average number of intravitreal injections and FU assessments over the 3 year data period. Patient level data in this study showed that patients received between 1 and 14 times in a year with significantly lower averages. However, the model inputs utilised distributions rather than these averages, for example, the distribution for FU assessments for observations is log-normal with mean of 1.4 and standard deviation (SD) of 0.37. According to the data, only 1% and 19% of treated and non-treated patients, respectively are discharged. Amongst those non-treated discharged patients, the vast majority are discharged at the end of year 1 and the discharge probability reduced dramatically from year 2 onwards (see Table 3 for details). In the UK, discharge from the hospital is the point at which the patient leaves the hospital and either returns home or is transferred to another facility. The number of patients who had no form of treatment (ie observations only) over the data period was 5505 ( Table 3). Out of this cohort the number of patients who attended in the last 2 years and were 'observation only' (ie persons who had no form of treatment) in the last 6 months was 894. This group of patients were referred to a nurse-led virtual clinic, where images are obtained from patients in absence of the clinician. The images were then reviewed subsequently by a clinician or other trained personnel who made disease management decisions. Extra capacity was achieved by referring 894 patients to a virtual clinic [18] in order to enable T&E regimen to be implemented. Table 4 displays the monthly average efficiencies that could be achieved through service re-design as forecasted by the model. Column 1 figures display the 'as is' , or current state for the service if it were to continue unchanged for each resource. The second column shows the impact of introducing a virtual clinic (with no change in current service), where 894 patients were seen. As these patients are shifted from current setting to the virtual clinic, we notice a reduction in all key metrics, e.g., number of follow-ups (from 726 to 642), and clinic session utilisation (71% to 64%). The model has included all costing and resourcing of running the virtual clinic. We also experimented where T&E is considered without the virtual clinic (third column). As expected, there is a sharp increase in the number of follow-ups, number of Anti-VEGF injections, and utilisation of resources. For instance, clinic and nurse utilisations has increased to a critical level of 85%, and without additional staff the system may not be able to cope with a slight increase in new attendances. This may not be a viable option, clearly showcasing the need to test the system with a combination of virtual clinics and T&E regime.

The fourth column shows the efficiencies generated comparing the current service against the combination of virtual clinics and T&E. A T&E regime in combination with a virtual clinic did not result in an increase in staff utilisation, but provided a noticeable increase in capacity with a 10% surplus. This provided the opportunity for investment in the service, with the increase in the quality of treatment and improvement in patient outcomes.

Discussion

The ever increasing demand in medical retinal services following the introduction of new therapies has resulted  in serious capacity constraints, such that some NHS clinics are failing to maintain the recommended follow-up/treatment intervals. This may have an increased risk of permanent vision loss, with huge impact on independence and quality of life of patients. It is, therefore, clear that robust and long term retinal service models that do not compromise visual outcomes, such as T&E in combination with virtual clinics, are required across NHS clinics in order to meet the needs of local populations currently and in the future. Such long-term management strategy of retinal disease in virtual clinics has been employed by a number Trusts in the UK and proven to be safe and effective if properly implemented [18]. The developed model is a new tool for forecasting and planning to support decision making in ophthalmology services. Using patient level data relating to the service, in conjunction with forecasting and simulation, enables a Trust to confidently predict the impact of making changes within the service. The flexibility of the model enables the impact of a wide range of scenarios to be tested (around several thousand scenarios can be tested). A potential solution (T&E in combination with virtual clinic) is presented here that is shown to improve quality, effectiveness and productivity and thus increase capacity. Despite the increase in the number of injections (with T&E), the impact on resource utilisation is negligible (almost 0%) and in some cases below 0%.

Spreadsheet based models commonly use averages, for example the average number of patients expected each day followed by the average number of patients who will be diagnosed with nAMD followed by the average number of injections in the first year. The problem with using averages in this way may lead to wildly incorrect predictions, commonly known as the 'error of averages' (Salvage, 2009) [21]. Arguably when considering services that have a turnover of many millions of pounds it is very important to be accurate.

Unlike spreadsheet models, the power of discrete event simulation in general is the ability to capture variability. For example, some guidelines assume that anti-VEGF treatments are injected on average of 7 times in the first year, although patient level data analysis in this study showed that there were 1-14 intravitreal injections in a year with significantly lower averages. As such assuming that all patients received an average of 7 injections per year could be misleading.

The choice of using simulation methods as opposed to analytical methods was partly dictated by the complexity of the pathway and the ease of use for end-users. In this respect, the need to track individual patient journeys (or trajectories) through the care system, the ability to capture the complex web of interactions of patients going through the diagnosis stage to various forms of treatment (including FUs) and the need to model notions of limited availability of resources (such as staff, beds, rooms and equipment) have motivated us to select discrete event simulation.

Instead of using averages our model uses each hospital Trusts' anonymised patient level data to track individual patients over a 36-month period. It counts the number of times a patient is treated and assessed in years 1, 2 and 3. It then uses statistical algorithms to establish the distribution, for example, treatment frequency for each year, for example log normal distribution with a mean and SD. The model is then run hundreds of times for thousands of patients where the distribution determines the number of times a patient is injected, as opposed to using an average of 7 injections per year for each patient. It is because the model pays close attention to these details, that it is able to create validated reports that are up to 95% accurate.

A constraint on modelling analysis is the recognition of essential resources that are required in order for an event to happen. For example, it is not possible for a clinic to start without a clinician. The model only starts a clinic when all the resources required are available. Intravitreal services are complex with many hundreds of variables/constraints. The ability to deal with these complex constraints simply does not exist in excel or any other modelling approaches. Using the model it is possible to show what happens if there is a variation in the availability of resources/constraints such as the increase or reduction in the number of clinic rooms available, or the effect of an absent clinician. Given the level of complexity and value of intravitreal services, it is extremely important to ensure that model outputs are robust and accurate. The National Institute for Health and Care Excellence (NICE) has recognised the methodology used in the model as a valid way of simulating complex patient pathways [22]. To the best of our knowledge, this model is currently the only simulation based planning tool for retinal service managers. Other such programmes or further development would be welcome.

Re-design of clinical services based on such programmes, nevertheless, requires investment, although such investment is outweighed by the potential increases in surplus generated from efficient service re-design. More importantly, optimum service re-design also leads to better quality of care that meet patients' needs, as well increased productivity by maximising the use of experienced clinicians. Furthermore, significant cost reductions are expected in the long-term as more patients retain their vision with better clinical outcomes due to the T&E or other similar regimen.

The authors are aware of the many difficulties that are faced in the planning, approval, and implementation of new retinal services. Changes can be introduced without proper consideration of the impact on the service, and as a result most business cases are inaccurate [12]. Frequently clinicians working within retinal services know how they would like to improve the service they deliver, but lack the expertise to frame those improvements in a manner that is acceptable to health service executives and managers who hold finance budget. The model was developed in conjunction with retinal specialists, specifically to address these issues. It is designed to allow 'non-experts' to test change on the pathway within the validated simulation. The simulation will present the impact of changes in a way that can be easily understood by both the healthcare executives and the pathway specialists. The intention is that this tool will facilitate service planning and decision making and speed up the pace of change in the retinal pathway.

The tool allows decision makers to develop a better understanding of key performance metrics associated with activity, cost implications and resource utilisation. The ease of use of the tool with relevant sets of exported results means that senior decision makers can be more proactive and confident with evidence based approach in re-designing their care pathway in finding the most efficient and effective delivery of care to patients with problems in the eye.

Conclusions

In conclusion, the model allows the use of pathway planning to improve clinic efficiency and patient outcomes without necessarily increasing costs in the long-term.

Additional file

Additional file 1: BMC HSR Data for simulation model. Table S5. Data used for the simulation model. Table providing

Availability of data and materials

The data entered in the model is included in the additional file "BMC Health Services Research paper additional file data for the model", which has been submitted with the paper. The National Tariff Payment System, NICE and MIMs data used to estimate some of the parameters in the model are publicly available. The links to the website and the date when it was accessed are available on the list of references of the paper (Reference numbers [20,23,24]). The dataset provided by Cambridge University Hospitals NHS Foundation Trust, which was used to estimate some of the parameters for the model, is held in the computer of one of the authors. It cannot be made publicly available as this is one of the conditions of acquiring the dataset. In addition, the data is not readable and needs database programming to be extracted, hence it cannot be made accessible.

Authors' contributions ED and DS conceptualise and developed the DES model. ED and WA wrote the paper with the contribution of DS and AV. All authors agreed on the final version of the paper. All authors read and approved the final manuscript.

Ethics approval and consent to participate Ethics approval and participant consent was not necessary as this study involved the use of the national Hospital Episodes Statistics (HES) dataset. Details about HES can be obtained at http://content.digital.nhs.uk/hes. In addition, the data collection for this study did not require ethics approval as: a) derived from secondary sources which are clearly set out in the paper, b) did not include any patient level identifiable data, c) did not include any patient/public participants, d) the study is categorized as a service evaluation using a consultation approach. The consultants, nurses and service managers involved in the research opted to participate. The interviews were not mandatory. Verbal consent was sought from the consultants, nurses and service managers, where participants had given full consent. As stated in Declarations section, UK ethical approval is not a compulsory requirement for studies which do not involve patients (see the following link for details http://www.hra.nhs.uk/documents/2013/09/does-my-project-require-recreview.pdf).

Consent for publication

Competing interests

David Southern is an employee of Pathway Communications. No conflicting relationship exists for the other authors regarding this article.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

First

details of parameters used in the simulation model including the source, distribution type and the value entered in the model. (DOCX 19 kb) Abbreviations A&E: Accident & Emergency; AMD: Age Related Macular Degeneration; anti-VEGF: anti-Vascular Endothelial Growth Factor; DNA: Did Not Attend; DR: Diabetic Retinopathy; FU: Follow-up; GP: General Practitioner; MR: Medical Retina; nAMD: neovascular Age Related Macular Degeneration; NHS: National Health Service; NICE: National Institute for Health and Care Excellence; PRN: Pro Re Nata; RVO: Retinal Vein Occlusion; SD-OCT: Spectral Domain Optical Coherence Tomography; T&E: Treat & Extend

Table 1
1Breakdown of activity by attended appointments during April 2013 -March 2016Activity
AMD DR
MR

No. of intravitreal injections
3295 425
743

No. of intravitreal injection related FU assessments 4851 599
955

No. of laser treatments
N/A
315
63

No. of laser related FU assessments
N/A
848
191

No. of observations
1208 4790 3846

Total
9354 6977 5798

Patients under observation refer to a group of patients who had no form of
treatment, hence under observation only

Table 2
2The average number of intravitreal injections and FU assessments over the 3 year data periodAMD
DR
MR

Year of treatment
Year of treatment
Year of treatment

Year
1

Year
2

Year
3

Year
1

Year
2

Year
3

Year
1

Year
2

Year
3

Table 3
3The number of discharged patients whether in treatment or under observation over 36 month's data period broken down by patient typeIn treatment Under observation Total

Number of discharged patients at the end of Year 1 of treatment

AMD
12
147
159

DR
1
330
331

MR
13
611
624

Number of discharged patients at the end of Year 2 of treatment

AMD
16
14
30

DR
5
32
37

MR
13
58
71

Number of discharged patients at the end of Year 3 of treatment

AMD
10
10
20

DR
1
24
25

MR
4
23
27

Total discharges
75 (1%)
1249 (19%)
1324 (20%)

Total non-discharges 950 (15%)
4256 (65%)
5206 (80%)

Total
1025 (16%)
5505 (84%)
6530 (100%)

Table 4
4The impact of current service against the combination of virtual clinics and treat and extendMonthly averages
Current
Service

Virtual Clinic + no change in current
service

Treat and Extend + no virtual
clinic

Virtual Clinic + Treat and
Extend

%
change

New attendances
119
119
119
119
0%

Follow-ups
726
642
812
708
−2%

Clinic session utilisation
71%
64%
85%
71%
0%

Nurse utilisation
71%
65%
82%
70%
−1%

Consultation room
utilisation

53%
48%
55%
51%
−4%

Injection bed utilisation
29%
30%
40%
37%
28%

Number of Anti-VEGF
injections

169
172
218
215
27%

Costing
£151,760
£153,963
£192,902
£190,200
25%

Revenue
£207,494
£207,494
£260,809
£251,664
21%

Surplus
£55,735
£53,532
£67,906
£61,464
10%

AcknowledgementsWe would thank Allergan
UK Vision Strategy. UK Vision Strategy 2013-18. 2013. https://www.visionuk.org.uk/refreshed-uk- vision-strategy-2013-18/. Accessed 14 Nov 2014.

The estimated prevalence and incidence of late stage age related macular degeneration in the UK. C G Owen, Z Jarrar, R Wormald, D G Cook, Br J Ophthalmol. 96Owen CG, Jarrar Z, Wormald R, Cook DG. The estimated prevalence and incidence of late stage age related macular degeneration in the UK. Br J Ophthalmol. 2012;96:752-6.

A variable-dosing regimen with intravitreal ranibizumab for neovascular age-related macular degeneration: year 2 of the PrONTO study. G A Lalwani, P J Rosenfeld, A E Fung, Am J Ophthalmol. 148Lalwani GA, Rosenfeld PJ, Fung AE, et al. A variable-dosing regimen with intravitreal ranibizumab for neovascular age-related macular degeneration: year 2 of the PrONTO study. Am J Ophthalmol. 2009;148:43-58.

Safety and efficacy of a flexible dosing regimen of ranibizumab in neovascular age-related macular degeneration: the SUSTAIN study. F G Holz, W Amoaku, J Donate, R H Guymer, U Kellner, R O Schlingemann, A Weichselberger, G Staurenghi, Sustain Study, Group, Ophthalmology. 118Holz FG, Amoaku W, Donate J, Guymer RH, Kellner U, Schlingemann RO, Weichselberger A, Staurenghi G, SUSTAIN Study Group. Safety and efficacy of a flexible dosing regimen of ranibizumab in neovascular age-related macular degeneration: the SUSTAIN study. Ophthalmology. 2011;118:663-71.

Current anti-vascular endothelial growth factor dosing regimens: benefits and burden. J A Haller, Ophthalmology. 120Haller JA. Current anti-vascular endothelial growth factor dosing regimens: benefits and burden. Ophthalmology. 2013;120:S3-7.

A treat and extend regimen using ranibizumab for neovascular age-related macular degeneration clinical and economic impact. O P Gupta, G Shienbaum, A H Patel, C Fecarotta, R S Kaiser, C D Regillo, Ophthalmology. 117Gupta OP, Shienbaum G, Patel AH, Fecarotta C, Kaiser RS, Regillo CD. A treat and extend regimen using ranibizumab for neovascular age-related macular degeneration clinical and economic impact. Ophthalmology. 2010;117:2134-40.

Treat-andextend bevacizumab for neovascular age related macular degeneration: the importance of baseline characteristics. R B Rush, M P Simunovic, L Vandiver, A V Aragon, J E Ysasaga, Retina. 34Rush RB, Simunovic MP, Vandiver L, Aragon AV 2nd, Ysasaga JE. Treat-and- extend bevacizumab for neovascular age related macular degeneration: the importance of baseline characteristics. Retina. 2014;34:846-52.

Changing from a pro re nata treatment regimen to a treat and extend regimen with ranibizumab in neovascular age-related macular degeneration. K Hatz, C Prünte, Br J Ophthalmol. 100Hatz K, Prünte C. Changing from a pro re nata treatment regimen to a treat and extend regimen with ranibizumab in neovascular age-related macular degeneration. Br J Ophthalmol. 2016;100:1341-5.

Treat and extend versus pro re Nata regimens of ranibizumab in neovascular age-related macular degeneration: a comparative 12 month study. K Hatz, C Prünte, 10.1111/aos.13031Acta Ophtholmol. 95Hatz K, Prünte C. Treat and extend versus pro re Nata regimens of ranibizumab in neovascular age-related macular degeneration: a comparative 12 month study. Acta Ophtholmol. 2017;95:e67-72. https://doi.org/10.1111/aos.13031.

Switching from pro re nata to treat-and-extend regimen improves visual acuity in patients with neovascular age-related macular degeneration. L Kvannli, J Krohn, 10.1111/aos.13356Acta Ophthalmol. Kvannli L, Krohn J. Switching from pro re nata to treat-and-extend regimen improves visual acuity in patients with neovascular age-related macular degeneration. Acta Ophthalmol. 2017. https://doi.org/10.1111/aos.13356.

The clinical effectiveness of Ranibizumab treat and extend regimen in nAMD: systematic review and network meta-analysis. A Danyliv, J Glanville, R Mccool, A Ferreira, A Skelly, R P Jacob, 10.1007/s12325-017-0484-0Adv Ther. Danyliv A, Glanville J, McCool R, Ferreira A, Skelly A, Jacob RP. The clinical effectiveness of Ranibizumab treat and extend regimen in nAMD: systematic review and network meta-analysis. Adv Ther. 2017. https://doi.org/10.1007/s12325-017-0484-0.

Action on AMD: Optimising patient management: act now to ensure current and continual delivery of best possible patient care. W Amoaku, S Blakeney, M Freeman, R Gale, R Johnston, S P Kelly, B Mclaughlan, D Sahu, D Varma, Eye. 26Amoaku W, Blakeney S, Freeman M, Gale R, Johnston R, Kelly SP, McLaughlan B, Sahu D, Varma D. Action on AMD: Optimising patient management: act now to ensure current and continual delivery of best possible patient care. Eye. 2012;26:S1-S21.

Implementation of medical retina virtual clinics in a tertiary eye care referral Centre. K Karsten, K Fasler, A Charnle, 10.1136/bjophthalmol-2017-311494Br J Ophthalmol. Karsten K, Fasler K, Charnle A, et al. Implementation of medical retina virtual clinics in a tertiary eye care referral Centre. Br J Ophthalmol. 2018. https://doi.org/10.1136/bjophthalmol-2017-311494.

The Portsmouth based glaucoma refinement scheme: a role for virtual clinics in the future?. S Trikha, C Macgregor, M Jeffery, J Kirwan, Eye. 26Trikha S, Macgregor C, Jeffery M, Kirwan J. The Portsmouth based glaucoma refinement scheme: a role for virtual clinics in the future? Eye. 2012;26:1288-94.

Qualitative investigation of patients' experience of a glaucoma virtual clinic in a specialist ophthalmic hospital in London. A Kotecha, K Bonstein, R Cable, J Cammack, J Clipston, P Foster, 10.1136/bmjopen-2015-009463UK. BMJ Open. 5129463Kotecha A, Bonstein K, Cable R, Cammack J, Clipston J, Foster P. Qualitative investigation of patients' experience of a glaucoma virtual clinic in a specialist ophthalmic hospital in London, UK. BMJ Open. 2015;5(12):e009463. https://doi.org/10.1136/bmjopen-2015-009463.

Experiences with developing and implementing a virtual clinic for glaucoma care in an NHS setting. A Kotecha, A Baldwin, J Brookes, P J Foster, Clin Ophthalmol. 9Kotecha A, Baldwin A, Brookes J, Foster PJ. Experiences with developing and implementing a virtual clinic for glaucoma care in an NHS setting. Clin Ophthalmol. 2015;9:1915-23.

Service innovation in glaucoma management: using a web-based electronic patient record to facilitate virtual specialist supervision of a shared care glaucoma programme. H R Wright, J P Diamond, Br J Ophthalmol. 99Wright HR, Diamond JP. Service innovation in glaucoma management: using a web-based electronic patient record to facilitate virtual specialist supervision of a shared care glaucoma programme. Br J Ophthalmol. 2015;99:313-7.

The concept of virtual clinics in monitoring patients with age-related macular degeneration. K T Tsaousis, T Empeslidis, V E Konidaris, B Kapoor, J Deane, Acta Ophthalmol. 94Tsaousis KT, Empeslidis T, Konidaris VE, Kapoor B, Deane J. The concept of virtual clinics in monitoring patients with age-related macular degeneration. Acta Ophthalmol. 2016;94:353-5.

NHS Reference Costs. NHS. RetrievedNHS Improvement (2017). NHS Reference Costs 2017. Retrieved June 13, 2017, from https://improvement.nhs.uk/resources/reference-costs/.

Ranibizumab and Pegaptanib for the treatment of age-related macular degeneration. NICERetrievedNICE (2013). Ranibizumab and Pegaptanib for the treatment of age-related macular degeneration. Retrieved June 20, 2017, from https://www.nice.org.uk/guidance/ta155/resources.

The flaw of averages: why we underestimate risk in the face of uncertainty. S Salvage, WileyNew JerseySalvage S. The flaw of averages: why we underestimate risk in the face of uncertainty. New Jersey: Wiley; 2009.

NICE DSU Technical support document 15: Cost effective modelling using patient level modelling. S Davis, M Stevenson, P Tappenden, A Wailoo, Davis S, Stevenson M, Tappenden P and Wailoo A. NICE DSU Technical support document 15: Cost effective modelling using patient level modelling. 2014. http://nicedsu.org.uk/wp-content/uploads/2016/03/TSD15_ Patientlevel_simulation.pdf. Accessed 1 Sept 2016.

2016/17 National Tariff Payment System. RetrievedPayment by Result (2017). 2016/17 National Tariff Payment System. Retrieved June 20, 2017, from https://www.gov.uk/government/ publications/nhs-national-tariff-payment-system-201617

Prescription drug database. Mims, RetrievedMIMS. (2017). Prescription drug database. Retrieved June 20, 2017, from http://www.mims.co.uk/


Acta Veterinaria Scandinavica A preliminary study on the induction of dioestrous ovulation in the mare -a possible method for inducing prolonged luteal phase

Ylva Hedberg email@example.com
Division of Comparative Reproduction, Obstetrics and Udder Health
Department of Clinical Sciences
Swedish University of Agricultural Sciences
P.O. Box 7054SE-750 07UppsalaSweden

Anne-Marie Dalin
Division of Comparative Reproduction, Obstetrics and Udder Health
Department of Clinical Sciences
Swedish University of Agricultural Sciences
P.O. Box 7054SE-750 07UppsalaSweden

Malin Santesson firstname.lastname@example.com
Division of Comparative Reproduction, Obstetrics and Udder Health
Department of Clinical Sciences
Swedish University of Agricultural Sciences
P.O. Box 7054SE-750 07UppsalaSweden

Hans Kindahl email@example.com
Division of Comparative Reproduction, Obstetrics and Udder Health
Department of Clinical Sciences
Swedish University of Agricultural Sciences
P.O. Box 7054SE-750 07UppsalaSweden

Acta Veterinaria Scandinavica A preliminary study on the induction of dioestrous ovulation in the mare -a possible method for inducing prolonged luteal phase
10.1186/1751-0147-48-12BioMed Central Page 1 of 6 (page number not for citation purposes) Research * Corresponding author
Background: Strong oestrous symptoms in the mare can cause problems with racing, training and handling. Since long-acting progesterone treatment is not permitted in mares at competition (e.g. according to FEI rules), there is a need for methods to suppress unwanted cyclicity. Spontaneous dioestrous ovulations in the late luteal phase may cause a prolongation of the luteal phase in mares.Methods:In this preliminary study, in an attempt to induce ovulation during the luteal phase, human chorionic gonadotropin (hCG) (3000 IU) was injected intramuscularly in four mares (experimental group) in the luteal phase when a dioestrous follicle ≥ 30 mm was detected. A fifth mare included in this group was not treated due to no detectable dioestrous follicles ≥ 30 mm. Four control mares were similarly injected with saline. The mares were followed with ultrasound for 72 hours post injection or until ovulation. Blood samples for progesterone analysis were obtained twice weekly for one month and thereafter once weekly for another two to four months.Results:Three of the hCG-treated mares ovulated within 72 hours after treatment and developed prolonged luteal phases of 58, 68 and 82 days respectively. One treated mare never ovulated after the hCG injection and progesterone levels fell below 3 nmol/l nine days post treatment. Progesterone levels in the control mares were below 3 nmol/l within nine days after saline injection, except for one mare, which developed a spontaneously prolonged luteal phase of 72 days.Conclusion: HCG treatment may be a method to induce prolonged luteal phases in the mare provided there is a dioestrous follicle ≥ 30 mm that ovulates post-treatment. However, the method needs to be tested on a larger number of mares to be able to draw conclusions regarding its effectiveness.

Background

According to many mare owners, strong oestrous symptoms result in difficulties with training and handling of the animal [1,2]. One method used earlier was to treat such mares with long-acting progesterone [3,4]. However, this treatment is not permitted for use in racing or compe-tition mares according to many European racing authorities, such as the British Jockey Club [5] and the Swedish Trotting Association (STC) [6], and also according to the rules of the International Federation for Equestrian Sports (FEI) [7]. In addition, in Sweden, short-acting progesterone treatment, such as altrenogest orally, is prohibited for use at competition in riding horses [8] and has a recommended drug withdrawal time of 14 days in Standardbred racehorses (personal communication, Peter Kallings). Another method, the crushing of embryos to achieve a prolonged progesterone phase, has recently been presented [9]; also, the insertion of glass or plastic balls into the uterus has been used to prolong the luteal phase in mares [10,11]. However, some consider these methods to be improper and the use of intrauterine balls is not permitted in Sweden in racing horses [6]. Therefore there is a need for alternative techniques. Mares, in contrast to females of other mammal species, have the ability to ovulate during dioestrus, when serum concentrations of progesterone are high. The frequency of dioestrous ovulations varies according to breed; in Thoroughbreds and Quarter Horses as many as 20 % of ovulations occur during the luteal phase [12], whereas the frequency of dioestrous ovulations is very low in ponies [13]. The follicles that grow and ovulate during dioestrus do not cause oestrous signs, due to the suppressive effects of progesterone on oestrous behaviour [12]. Spontaneous dioestrous ovulations that occur between one to four days prior to luteolysis may cause a prolonged luteal phase, due to the immature corpus luteum being refractory to prostaglandins, as shown by exogenous prostaglandin treatment [14]. A refractory state to endogenous prostaglandin for up to four days after ovulation was also demonstrated by the use of intrauterine saline infusion [15,16]. The normal mean dioestrous length, derived from several different reports, is 14.9 days (range 12.1 to 16.3 days) [17] and in one study, prolonged luteal phases lasted for a mean of 63 days (range 35-96 days) [18]. Daels et al. [19] demonstrated that ovulation induced by human chorionic gonadotropin (hCG) during altrenogest treatment could lead to a prolonged luteal phase (5/6 of the mares that ovulated). The present study was designed to evaluate if hCGinduced ovulation during the late luteal phase in mares will cause a prolonged luteal phase. Both the method of Daels et al. [19] and the method used in the present study would eliminate oestrous behaviour for a period of time due to high endogenous progesterone levels. However, an advantage with the method presented in this paper, as compared to the method of Daels et al. [19], is that exogenous altrenogest treatment is not used.

Methods

Animals, management and housing

The experiment was performed in April-September 2004. All procedures were approved by the Ethical Committee for Experimentation with Animals, Sweden. Nine mares weighing between 450 and 550 kg and with an age span of four to 20 years were used in the study. Eight of the mares were Standardbred trotters and one was a Swedish warmblood mare (mare A). The mares were kept at the Division of Comparative Reproduction, Obstetrics and Udder Health, Department of Clinical Sciences and were all owned by the department. From the first week of December 2003, the mares were put on light treatment for 16 hours per day. Prior to the experimental period, the mares had been teased daily with a stallion, which showed that all mares had normal oestrous cycle lengths for at least two cycles before commencing the study (three cycles in all mares but one). In April and May, all mares were stabled indoors on straw in individual loose boxes during the night and let out at pasture during the day (approximately 08.00 to 15.00 h). The mares were fed grass hay (morning, noon and evening) and a small amount of oats, soaked sugar beet and a mineral supplement (afternoon). From the first week of June and after at least one month of experimental study at the department, seven of the mares were transported to pasture 30 km away from the department, where they were kept outdoors 24 hours per day until the end of the study. The mares always had free access to water. One mare (mare T) was moved to pasture after only 15 days of study; she had received hCG, but did not ovulate and showed symptoms of oestrus at the department before being moved.

Experimental procedure

The mares were randomly divided into an experimental group (n = 5) and a control group (n = 4). When the mares were at the department, teasing with a stallion was performed daily and oestrous signs were scored as follows: + 1 for tail raise, + 1 for clitorial winking/urination and + 1 for standing in a straddled posture, with behavioural oestrus defined as a score of + 2 or above. When behavioural oestrus was detected, transrectal ultrasound examination (six MHz linear probe, 485 Anser, Pie Medical, Maastricht, Netherlands) of the uterus and ovaries was performed every other day until ovulation was confirmed. Thereafter, from approximately day eight after ovulation in dioestrus, transrectal ultrasound examination was again performed every other day to determine the size of the dioestrous follicles. Three mares (mares Ev, Ma and L) were for technical reasons not examined at oestrus and only followed from day eight after the last oestrous signs were detected; they had a corpus luteum and high progesterone levels at treatment. When a follicle ≥ 30 mm of diameter was detected, 3000 IU of hCG (Pregnyl ® , Organon AB, Gothenburg, Sweden) or an equal volume of saline (2 ml) was injected intramuscularly. The mares were then followed with ultrasound for up to 72 hours or until ovulation. Thereafter the mares were examined with ultrasound once weekly for three weeks. One mare (mare T) was only examined twice after treatment; she had not ovulated after the hCG injection and showed oestrous signs during teasing eight days after treatment. Starting on the treatment day (hCG or saline), samples for progesterone analysis were obtained from the jugular vein into a heparinised evacuated tube. Thereafter, blood samples for progesterone analysis were taken twice weekly for at least one month and then once weekly for another two to four months. One mare (mare A) was only sampled once a week for the whole duration of the study. This mare, however, was teased daily and examined with ultrasound once or twice per week throughout the study period. In two mares (mares Ex and A) two and one of the samples, respectively, were taken eight or nine days apart (see Fig.  1). All blood samples were immediately centrifuged and the plasma stored at -20°C. Mares were defined as being in luteal phase if progesterone values were above 3 nmol/ l [17] in samples taken twice weekly and above 10 nmol/ l in samples taken once weekly [20,21]. If no follicles with a size of at least 30 mm were detected in one dioestrous period, the mares were followed as above for, at most, a total of three luteal phases.

Hormone analysis

The concentration of progesterone in peripheral blood plasma was determined using a solid-phase radioimmunoassay (Coat-a-Count Progesterone, Diagnostic Products Corporation, Los Angeles, USA). The kit was used according to the manufacturer's instructions. The relative crossreactions of the antibody were 0.9 % with corticosterone and 0.1 % with testosterone. The intra-assay coefficients of variation for progesterone were as follows: 1.4 % at 3.4 nmol/l; 5.2 % at 24.2 nmol/l; 4.1 % at 56.1 nmol/l. The minimal assay sensitivity of progesterone was 0.1 nmol/l.

Results

The main results are summarised in Table 1. Three of nine mares developed follicles that were above 30 mm (and thus could be treated) in the first luteal phase examined. The remaining mares developed large enough follicles in the second (n = 4), third (n = 1) or in none (n = 1) of the luteal phases studied. Depending on if a mare was treated in the first, second or third dioestrous period after the start of the experiment (due to follicle size), mares were followed for between 90 to 160 days after treatment. Three of the four hCG-treated mares ovulated, resulting in luteal phases, as defined in materials and methods, lasting for 58, 68 and 82 days post-treatment respectively ( Table 1). Figure 1 shows their post-treatment progesterone concentrations. These mares were treated between eight and ten days after ovulation was confirmed by ultrasound (every other day) or after last detected oestrous signs (mare Ev), which means their actual luteal phases lasted for at least 69, 77 and 90 days. Two of the hCG-treated mares (mares A and Ev) were never moved to pasture and were therefore teased daily for symptoms of oestrus and mare A examined with ultrasound. The mares showed oestrous signs at days 62 (mare Ev) and 88 (mare A) post treatment and their progesterone levels were then below 3 nmol/l. Mare A had two additional luteal phase ovulations which were associated with two peaks in her progesterone levels (see Fig. 1). The third mare (mare Ex) did not show any symptoms of oestrus during the time she was still kept at the department (37 days). One additional mare in the experimental group (mare O) never developed a dioestrous follicle above 30 mm in any of the three luteal phases studied and was thus never treated. Another mare in this group (mare T) injected with hCG in the third luteal phase studied did not ovulate as a result, although she had a follicle above 30 mm at treatment. This mare showed symptoms of oestrus eight days after the injection had been given. The progesterone level was then low (< 3 nmol/l).

None of the control mares treated with saline ovulated during the luteal phase. In three mares (mares Ma, L and J), progesterone values dropped below 3 nmol/l within nine days post-injection. Two of these mares (mares Ma and L) showed oestrous symptoms in association with the drop in progesterone resulting in dioestrous lengths of 18 and 23 days respectively. Mare J had silent oestrus and ultrasound examination three days after the low progesterone values revealed a new corpus luteum (soft on palpation) and progesterone levels increased to 28 nmol/l four days later. Mare Me never developed a follicle ≥ 30 mm in the first luteal phase studied and got a spontaneous prolongation of this luteal phase. Therefore, she was induced with prostaglandin F 2α (on day 22 of dioestrus) (1 ml Dinolytic ® vet., 5 mg, Orion, Animal Health, Sollentuna, Sweden). She also developed a spontaneously prolonged luteal phase after the saline treatment that lasted Progesterone levels in hCG treated mares that ovulated after treatment Figure 1 Progesterone levels in hCG treated mares that ovulated after treatment. 'a' and 'b' = peaks associated with formation of corpora lutea. * = samples taken 8 or 9 days apart. Dashed lines show the cut-off levels for progesterone samples taken twice weekly (3 nmol/l) or once weekly (10 nmol/l)  Figure 2 shows mare Me's progesterone levels during the study and also the progesterone levels of mare J for comparison with a mare that cycled normally. Mare Me showed no symptoms of oestrus after saline treatment during the time she was kept at the department (28 days).

Progesterone analysis of all of the samples showed that one of the control mares (mare Ma) that came into oestrus after the saline injection thereafter developed a prolonged luteal phase lasting for 76 days.

Discussion

In the present study, the fact that immature corpora lutea do not respond to the luteolytic effect of endogenous prostaglandin was utilised in an attempt to produce a pro-longed luteal phase [15,16,22]. The mares in the hCG treatment group that developed prolonged luteal phases ovulated between days ten and 13 in dioestrus. Thus, the corpora lutea were a maximum of four days old, and presumably refractory, at the time of endogenous prostaglandin release which occurs around days 14 to 17 of dioestrus [22,23]. Failure of the endometrium to release prostaglandin at the time of luteolysis (for example due to chronic endometritis, maternal recognition of pregnancy or for idiopathic reasons) can also cause a prolonged luteal phase in the mare [23][24][25][26][27]. It would have been of interest to measure prostaglandin metabolite levels to rule out that impaired prostaglandin release was not a cause of the prolonged luteal phases. Unfortunately, this was for practical reasons not possible in the present study. Although all of the mares had shown normal cycle lengths prior to the study, one mare (mare Me) developed a prolonged luteal phase in the first cycle studied and also, in the subsequent, saline treated, cycle.

The mares that ovulated as a result of the hCG treatment developed prolonged luteal phases that lasted for approximately two to three months. Other studies have also shown prolonged luteal activity in the mare to last for similar lengths of time [28,29]. It has been proposed that in order for the uterus to produce and release prostaglandin in response to oxytocin (as occurs at luteolysis), a period of low progesterone levels (i.e. oestrus) followed by a period with elevated progesterone concentrations (i.e. dioestrus), is required [27,30,31]. An initial prolongation of the luteal phase, where a drop in progesterone levels does not occur at the expected time, seems to render the uterus less sensitive to oxytocin [27]. This in turn results in impaired prostaglandin synthesis and release and a prolonged luteal phase lasting for up to three months. For unknown reasons, the uterus eventually regains its responsiveness and oxytocin induced prostag-Progesterone levels after saline treatment in two control mares

Saline

Mare Ma one 10* -----8 days Mare Me two 7 -----72 days Mare J two 7 -----8 days Mare L two 9* -----9 days * Day after last oestrous signs landin production is again possible, finally resulting in luteolysis and oestrus [27,29].

It has been suggested that prolonged luteal activity may be caused by more than one corpora lutea developing in succession rather than by the persistence of a single corpus luteum [32]. In the present study, the luteal phase length was determined by progesterone analysis alone, and therefore it is not known if the corpora lutea developed as a result of the hCG treatment was active throughout the whole prolonged luteal phase or whether subsequent corpora lutea developed. One mare (mare A), however, was examined with ultrasound throughout the study. In that mare, two peaks in the progesterone curve were found to be associated with two ovulations during the luteal phase (in addition to the hCG induced ovulation), which might have contributed to the increased progesterone levels (see Fig. 1).

Of the mares that ovulated as a result of the hCG injection, 100 % (3/3) developed prolonged luteal phases, i.e. 75 % of the total number of hCG-treated mares. Among the control mares, 25 % (1/4) developed a spontaneously prolonged luteal phase in the saline treated cycle (this mare showed prolonged luteal activity twice during the study; see results). In the oestrous cycle following the saline treated cycle, another mare developed a spontaneously prolonged luteal phase. Thus, in total, 2/4 control mares showed prolonged luteal activity. The incidence of so-called spontaneous prolongation of luteal activity in the mare has been reported to be common in some breeds. One study following seven mares (Thoroughbreds and Quarter Horses) over a two-year period reported 12 cases of prolonged luteal phase [29]. Another study has reported an incidence of prolonged luteal phase of only 3.6 % in trotter mares [33].

According to Fortune [34], only about one third of mares have a secondary follicular wave. Other studies, however, show that the majority of mares do have a secondary follicular wave that occurs during dioestrus, which is accompanied by a rise in FSH and can lead to ovulation [18,35]. Breed differences may explain these divergent findings. Studies have demonstrated that Thoroughbreds have a higher incidence of two major waves compared to Standardbreds, Quarter horses and ponies [17,36]. The present study indicates that maximum follicular size during dioestrus may vary within the same animal and that some mares may never develop large follicles (> 30 mm) in the luteal phase. Perhaps using Thoroughbreds as opposed to Standardbreds would have shown different results.

One hCG treated mare with a dioestrous follicle above 30 mm did not ovulate as a result of the treatment. Few studies have been performed on what the optimal follicle size is when inducing ovulation with hCG, although most studies use 35 mm as minimal size when mares are in oestrus, which is also followed in practice [27,37,38]. That the follicle is actively growing, and not in regression, is probably crucial [17]. The reason for selecting a follicle size of 30 mm or above was because it was suspected that few mares would develop very large follicles in dioestrus, which also was confirmed. The follicle of one mare did not ovulate after hCG-treatment, maybe because of the immaturity of the follicle. It has been shown that only follicles with nine to ten granulosa cell layers respond to FSH and continue their growth and that only a few of these follicles are able to ovulate [34]. Oestrogen and androgen production by the follicle seems to be important in its final maturation and it has been demonstrated that follicles developing during the luteal phase produce less oestrogens, which may result in dioestrous follicles being less responsive to hCG [34].

Thus, there are limitations to the usefulness of the present method in practice. Mares may have to be followed for more than one luteal phase before a follicle of suitable size is detected and some mares may never develop large enough follicles. Also, even if the follicle is larger than 30 mm, it is not certain that ovulation will occur. However, modifying the method by using repeated injections of hCG in smaller doses may give better results. Ovulation of follicles as small as 20 mm has been achieved using 200 IU of hCG given daily (seven out of eight pony mares ovulated in a mean of nine days) [39].

Conclusion

As a method of inducing prolonged luteal phase in the mare, the results of this preliminary study may suggest the use of hCG in the late luteal phase, providing a follicle greater than 30 mm is present and ovulates as a result of the treatment. The method does not involve the use of substances banned for competition purposes and could thus potentially be used for competition mares whose performance is affected by the oestrous cycle. However, to conclude that the method is effective and applicable to practice, it is necessary to repeat the study using a larger number of mares.

the manuscript. All authors read and approved the final manuscript.

Figure 2
2Progesterone levels after saline treatment in two control mares. Mare Me developed a spontaneously prolonged luteal phase. Dashed lines show the cut-off levels for progesterone samples taken twice weekly (3 nmol/l) or once weekly (10 nmol/l)

Table 1 :
1Summary of results of saline-and hCG-treated maresTreatment
Mare
Cycle no. treated
Day after confirmed ovulation
Length of luteal phase after
treatment

treatment was
given

new ovulation was
detected

hCG (3000 IU) Mare A
two
8
10
82 days
Mare Ev one
10*
13
58 days
Mare Ex one
10
13
68 days
Mare T
three
10
-----
9 days

(page number not for citation purposes)
AcknowledgementsThe authors wish to express their gratitude to Mari Wallbring, Carola Jansson and Ulrika Mattsson for handling the mares and assisting with the blood sampling.Competing interestsThe author(s) declare that they have no competing interests.Authors' contributionsAll authors participated in the design of the study. YH, MS and AMD examined the mares and participated in sample collection. MS analysed the blood samples. YH and MS drafted the manuscript. AMD and HK conceived of the study, participated in its coordination and helped to draft
Nymphomania in the mare. C Lindström, Master thesis Swedish University of Agriculture. Faculty of Veterinary Medicine; 2000.. In SwedishLindström C: Nymphomania in the mare. In Master thesis Swed- ish University of Agriculture, Faculty of Veterinary Medicine; 2000. (In Swedish)

Effect of oestrous cycle stage on the response of mares in a novel object test and isolation test. Y Hedberg, A-M Dalin, P Öhagen, K R Holm, H Kindahl, Reprod Dom Anim. 40Hedberg Y, Dalin A-M, Öhagen P, Holm KR, Kindahl H: Effect of oestrous cycle stage on the response of mares in a novel object test and isolation test. Reprod Dom Anim 2005, 40:480-488.

Mild form of nymphomania in the horse. T Tagbøl, Ø Andresen, R Thomassen, Effect of gestagen treatment in racehorses. Proceedings Nordic Mastitis and Reproduction Meeting. Trondheim. TownIn NorwegianTagbøl T, Andresen Ø, Thomassen R: Mild form of nymphomania in the horse. Effect of gestagen treatment in racehorses. Pro- ceedings Nordic Mastitis and Reproduction Meeting: 1991; Trondheim. Town 1991:115-121. (In Norwegian)

Effect of progesterone treatment in mild nymphomania in the mare. J Christensson, Svensk Veterinärtidning. 43In SwedishChristensson J: Effect of progesterone treatment in mild nym- phomania in the mare. Svensk Veterinärtidning 1991, 43:111-115. (In Swedish)

. The British Jockey Club. The British Jockey Club [http://www.thejockeyclub.co.uk]

. International Federation for Equestrian Sports. FEISwedish trotting association (STCSwedish trotting association (STC) [http://www.travsport.se] 7. International Federation for Equestrian Sports (FEI) [http:// www.horsesport.org]

Nonpharmacological suppression of oestrus in the mare. A C Lefranc, W R Allen, Equine Vet J. 36Lefranc AC, Allen WR: Nonpharmacological suppression of oestrus in the mare. Equine Vet J 2004, 36:183-185.

Modifying estrus behavior in mares-an alternative approach. G J Nie, K E Johnson, T D Braden, Jgw Wenzel, Proceedings Annual Conference Society for Theriogenology. Annual Conference Society for TheriogenologyVancouverNie GJ, Johnson KE, Braden TD, Wenzel JGW: Modifying estrus behavior in mares-an alternative approach. Proceedings Annual Conference Society for Theriogenology: 12-15 September 2001; Vancouver 2001:225-227.

Inhibition of oestrus in mares using intrauterine devices. Abstract OC5.1. Reprod Dom Anim. M M Rivera Del Alamo, T Reilas, T Katila, 40343Rivera del Alamo MM, Reilas T, Katila T: Inhibition of oestrus in mares using intrauterine devices. Abstract OC5.1. Reprod Dom Anim 2005, 40:343.

J P Hughes, A C Marcelo, G H Stabenfeldt, Luteal phase ovulations: what are the options? Proceedings of Annual Meeting of the Society of Theriogenology. SacramentoHughes JP, Marcelo AC, Stabenfeldt GH: Luteal phase ovulations: what are the options? Proceedings of Annual Meeting of the Society of Theriogenology: 11-13 September 1985; Sacramento 1985:123-125.

Influence of season and age on reproductive activity in pony mares on the basis of a slaughterhouse survey. J A Wesson, O J Ginther, J Anim Sci. 52Wesson JA, Ginther OJ: Influence of season and age on repro- ductive activity in pony mares on the basis of a slaughter- house survey. J Anim Sci 1981, 52:119-129.

Effects of prostaglandin F 2α on estrous cycle or corpus luteum in mares and gilts. R H Douglas, O J Ginther, J Anim Sci. 40Douglas RH, Ginther OJ: Effects of prostaglandin F 2α on estrous cycle or corpus luteum in mares and gilts. J Anim Sci 1975, 40:518-522.

Influence of intrauterine saline infusion upon the oestrous cycle of the mare. G H Arthur, J Reprod Fert. Arthur GH: Influence of intrauterine saline infusion upon the oestrous cycle of the mare. J Reprod Fert 1975:231-234.

Studies on the control of luteal function and prostaglandin release in the mare. D P Neely, PhD Thesis University of California. DavisNeely DP: Studies on the control of luteal function and pros- taglandin release in the mare. In PhD Thesis University of Cali- fornia, Davis; 1979.

O J Ginther, Reproductive Biology of the Mare: Basic and Applied Aspects. Wisconsin: Equiservices2nd editionGinther OJ: Reproductive Biology of the Mare: Basic and Applied Aspects 2nd edition. Wisconsin: Equiservices; 1992.

The estrous cycle and selected functional and pathologic ovarian abnormalities in the mare. J P Hughes, G H Stabenfeldt, P C Kennedy, Symposium on Equine Reproduction. 2Hughes JP, Stabenfeldt GH, Kennedy PC: The estrous cycle and selected functional and pathologic ovarian abnormalities in the mare. Symposium on Equine Reproduction 1980, 2:225-239.

Persistence of the luteal phase following ovulation during altrenogest treatment in mares. P F Daels, P M Mccue, M J Demoraes, J P Hughes, Theriogenology. 46Daels PF, McCue PM, DeMoraes MJ, Hughes JP: Persistence of the luteal phase following ovulation during altrenogest treat- ment in mares. Theriogenology 1996, 46:799-811.

Milk and serum progesterone levels in mares after ovulation. E Koskinen, H Lindeberg, H Kuntsi, T Katila, Acta vet scand. 31Koskinen E, Lindeberg H, Kuntsi H, Katila T: Milk and serum pro- gesterone levels in mares after ovulation. Acta vet scand 1990, 31:441-444.

Serum progesterone levels in mares in winter and during transitional periods. E Koskinen, M Huhtinen, T Katila, Acta vet scand. 37Koskinen E, Huhtinen M, Katila T: Serum progesterone levels in mares in winter and during transitional periods. Acta vet scand 1996, 37:409-414.

The influence of intrauterine saline infusion on luteal function and cyclical activity in the mare. D P Neely, J P Hughes, G H Stabenfeldt, J W Evans, J Reprod Fert. Neely DP, Hughes JP, Stabenfeldt GH, Evans JW: The influence of intrauterine saline infusion on luteal function and cyclical activity in the mare. J Reprod Fert 1975:235-239.

Prostaglandin release patterns in the mares: physiological, pathophysiological, and therapeutic responses. D P Neely, H Kindahl, G H Stabenfeldt, L-E Edqvist, J P Hughes, J Reprod Fert. 1979Neely DP, Kindahl H, Stabenfeldt GH, Edqvist L-E, Hughes JP: Pros- taglandin release patterns in the mares: physiological, patho- physiological, and therapeutic responses. J Reprod Fert 1979:181-189.

Pyometra in the mare. J P Hughes, G H Stabenfeldt, H Kindahl, P C Kennedy, L-E Edqvist, D P Neely, O W Schalm, J Reprod Fert. Hughes JP, Stabenfeldt GH, Kindahl H, Kennedy PC, Edqvist L-E, Neely DP, Schalm OW: Pyometra in the mare. J Reprod Fert 1979:321-329.

Control of luteolysis in the mare. G H Stabenfeldt, H Kindahl, J P Hughes, D P Neely, I Liu, D Pascoe, Acta vet scand. Stabenfeldt GH, Kindahl H, Hughes JP, Neely DP, Liu I, Pascoe D: Control of luteolysis in the mare. Acta vet scand 1981:159-170.

Progesterone, prostaglandin F-2α, PMSG and oestrone sulphate during early pregnancy in the mare. H Kindahl, O Knudsen, A Madej, L-E Edqvist, J Reprod Fert. 1982Kindahl H, Knudsen O, Madej A, Edqvist L-E: Progesterone, pros- taglandin F-2α, PMSG and oestrone sulphate during early pregnancy in the mare. J Reprod Fert 1982:353-359.

Changes in PGF 2α secretion during prolonged luteal phase in mares. H Kindahl, K Odensvik, B Hansen, P F Daels, J Reprod Fert. Kindahl H, Odensvik K, Hansen B, Daels PF: Changes in PGF 2α secretion during prolonged luteal phase in mares. J Reprod Fert 2000:305-315.

The oestrous cycle of the mare. J P Hughes, G H Stabenfeldt, J W Evans, J Reprod Fert. Hughes JP, Stabenfeldt GH, Evans JW: The oestrous cycle of the mare. J Reprod Fert 1975:161-166.

Spontaneous prolongation of luteal activity in the mare. G H Stabenfeldt, J P Hughes, J W Evans, D P Neely, Equine Vet J. 6Stabenfeldt GH, Hughes JP, Evans JW, Neely DP: Spontaneous pro- longation of luteal activity in the mare. Equine Vet J 1974, 6:158-163.

Uterine prostaglandin release relative to embryo collection, transfer procedure and maintenance of the corpus luteum. K J Betteridge, Renard A Geoff, A K , Equine Vet J. Betteridge KJ, Renard A, Geoff AK: Uterine prostaglandin release relative to embryo collection, transfer procedure and maintenance of the corpus luteum. Equine Vet J 1985:25-33.

Ovarian response in mares to prolonged treatment with exogenous equine pituitary gonadotrophins. S Hoeffer, G Duchamp, E Palmer, J Reprod Fert. Hoeffer S, Duchamp G, Palmer E: Ovarian response in mares to prolonged treatment with exogenous equine pituitary gona- dotrophins. J Reprod Fert 1991:341-349.

Prolonged luteal activity in mares-a semantic quagmire. O J Ginther, Equine Vet J. 22Ginther OJ: Prolonged luteal activity in mares-a semantic quagmire. Equine Vet J 1990, 22:152-156.

Prolonged luteal activity in the mare. J P Henry, M Coryn, J Spincemaille, M Vandeplassche, Zuchthyg. 16Henry JP, Coryn M, Spincemaille J, Vandeplassche M: Prolonged luteal activity in the mare. Zuchthyg 1981, 16:145-153.

Ovarian follicular growth and development in mammals. J E Fortune, Biol Reprod. 50Fortune JE: Ovarian follicular growth and development in mammals. Biol Reprod 1994, 50:225-232.

Serum concentrations of FSH, LH and progesterone during the oestrous cycle and early pregnancy in the mare. M J Evans, Chg Irvine, J Reprod Fert. Evans MJ, Irvine CHG: Serum concentrations of FSH, LH and progesterone during the oestrous cycle and early pregnancy in the mare. J Reprod Fert 1975:193-200.

Follicular population dynamics during the estrous cycle of the mare. R A Pierson, O J Ginther, Anim Reprod Sci. 14Pierson RA, Ginther OJ: Follicular population dynamics during the estrous cycle of the mare. Anim Reprod Sci 1987, 14:219-231.

Retrospective study on the efficacy of hCG in an equine artificial semination programme using frozen semen. S Barbacini, G Zavaglia, V Marchi, D Necchi, Equine Vet Ed. 12Barbacini S, Zavaglia G, Marchi V, Necchi D: Retrospective study on the efficacy of hCG in an equine artificial semination pro- gramme using frozen semen. Equine Vet Ed 2000, 12:312-317.

Simplified strategy for insemination of mares with frozen semen. E L Squires, S Barbacini, D Neechi, H P Reger, J E Bruemmer, Squires EL, Barbacini S, Neechi D, Reger HP, Bruemmer JE: Simpli- fied strategy for insemination of mares with frozen semen.

Annual Convention of the American Association of Equine Practitioners. International Veterinary Information Service. Annual Convention of the American Association of Equine Practition- ers: 2003; New Orleans, Louisiana [http://www.ivis.org]. International Veterinary Information Service, Ithaca, New York, USA

Stimulation of ovarian activity in the pony mare during winter anoestrus. B Bour, E Palmer, M A Driancourt, Endocrine Causes of Seasonal and Lactational Anestrus in Farm Animals Edited by: Ellendorff F, Elsaesser F. BostonMartinus Nijhoff Publishers1985Bour B, Palmer E, Driancourt MA: Stimulation of ovarian activity in the pony mare during winter anoestrus. In Endocrine Causes of Seasonal and Lactational Anestrus in Farm Animals Edited by: Ellendorff F, Elsaesser F. Boston: Martinus Nijhoff Publishers; 1985:85-97.