extreme ambient temperature is probably the most prevalent environmental stressor adversely affecting welfare , health , and production economics in broiler industry ( borges et al . the major consequence of heat stress in growing birds is depressed weight gain occurring mainly due to decreased feed intake and elevated energy expenditure to reduce body temperature ( lott 1991 ; may and lott 1992 ; belay and teeter 1993 ) . therefore , exploration of any avenue toward heat stress relief which improves feed and water intake may offer a thermoregulatory and performance advantage to heat - stressed broilers . many studies have focused on diet modifications to alleviate hot environmental conditions for heat - stressed broilers . in most of these studies , supplementing diets or drinking water with vitamins ( mckee and harrison 1995 ) , electrolytes ( borges et al . 2003 , 2004 ; ahmed and sarwar 2006 ) , probiotics ( zulkifli et al . 2000 ) , prebiotics ( riad et al . 2010 ) , or organic acids ( goksoy et al . 2010 ) was the main approach suggested to minimize the impact of heat stress in broilers . recent findings show that the use of phytogenic feed additives alleviates the harmful effect of heat stress in broiler chickens ( zeinali et al . ( 2011 ) reported that dietary supplementation of selenium and turmeric powder had a beneficial effect on health and plasma lipids in heat - stressed broiler chicken . suderman and solikhah ( 2011 ) showed that inclusion of pluchea indica l. leaf meal in diet ( 20  g / kg ) improved weight gain , feed intake , and water intake , but not feed conversion ratio , in heat - stressed broiler chicks . satureja khuzistanica jamzad is a plant well - known for its remedial properties in traditional medicine ( zargari 1990 ) . the aerial parts of s. khuzistanica collectively contain up to 3  % of an essential oil spectacularly rich in carvacrol ( up to 94  % ) ( khosravinia et al . carvacrol is a phenolic , caustic , and bitter - tasting compound with good stability ( lide 1998 ) demonstrating antioxidant ( quiroga and asensio 2015 ) and antimicrobial ( burt 2004 ) effects . therefore , the s. khuzistanica essential oils ( skeo ) exhibited antioxidant ( abdollahi et al . 1998 ) , antibacterial ( azaz et al . 2002 ) , and antifungal ( skocibusic and bezic 2004 ) effects mainly in experiments conducted under standard managerial practices and normal environmental conditions . however , experimental evidence on effects of administration of phytogenic extracts to the avian exposed to various environmental stressors such as heat - stressed birds is scarce . therefore , this study aimed to examine the effects of skeo on productive performance , mortality , and certain organ weights in broiler chickens exposed to seasonal extreme environmental temperatures during days 21 to 42 of age . the aerial parts of s. khuzistanica were manually harvested during the flowering stage of the plant in khorraman farm , khorramabad , iran.1 the collected materials were air dried at ambient temperature under shade and hydrodistilled using a clevenger - type apparatus for 5  h , giving a yellow oil in 3  % yield . a sample of the bulk was analyzed based on the methods used by hadian et al . ( 2011 ) and the composition is presented in table  1.table 1essential oil composition of satureja khuzistanica 
 compoundri1composition ( % ) 
 -thujene9250.24    0.14 
 -pinene9330.15    0.05myrcene9810.26    0.19 
 -terpinene10130.24    0.12 
 p - cymene10171.26    0.86limonene10260.13    0.04(z)--ocimene10360.54    0.08 
 -terienene10530.74    0.23 
 trans - sabinene hydrate10810.17    0.02terpinen-4-ol1163tr 
 -terpinolene11750.42    0.45thymol1266trcarvacrol128292.16    0.46thymyl acetate1329tr 
 -caryophyllene14250.16    0.01 
 -humulene1427tr 
 -bisabolene1501tr 
 trans--bisabolene15220.10    0.01 
 ri1 retention indices determined relative to n - alkanes ( c6c24 ) on a db-5gc column , tr trace ( < 0.05  % ) essential oil composition of satureja khuzistanica 
 
 ri1 retention indices determined relative to n - alkanes ( c6c24 ) on a db-5gc column , tr trace ( < 0.05  % ) a total number of 720 1-day - old arian broiler chicks were obtained from a commercial hatchery and housed in a concrete floor , cross - ventilated windowless shed . the chicks were randomly assigned to 36 pens ( 100    180  cm ) arranged in six replicate blocks at flocking density of 12 birds per m. corn and soybean meal based diets and water were provided to the birds for ad libitum consumption throughout the experiment ( table 2 ) . the shed was equipped with wet pad - and - fan cooling system to reduce the ambient temperature . nonetheless , during days 21 to 42 of experiment , the average temperature during day and night hours ranged from 32 to 35 and 28 to 30  c , respectively . therefore , it was considered that the birds were exposed to seasonal extreme ambient temperature from day 21 of age onwards.table 2percentage inclusion and calculated composition of dietsingredient ( % ) prestarter , 17  daysstarter , 721  daygrower , 2235  daysfinisher , 3642  dayscorn53.0055.3557.0061.00soybean meal25.0023.1222.520.5fish meal7.005.004.003.00soybean oil4.004.004.005.00wheat3.504.003.502.50calcium carbonate2.002.002.002.00wheat bran2.502.003.003.00dicalcium phosphate2.002.002.002.00dl - methoinine0.200.200.200.20 
 l - lysine0.120.110.100.10common salt0.250.250.250.25mineral premix 
 0.500.500.500.50vitamin permix 
 0.750.650.550.50coccidiostat0.100.100.100.00calculated composition  me , mj / kg12.3912.0512.3512.52  crude protein , % 22.2421.1520.0217.63  calcium , % 1.101.031.001.01  available p , % 0.450.440.400.45  methionine , % 0.520.530.400.43  lysine , % 1.151.081.101.03 
 mineral mix supplied per kilogram diet : mn , 55  mg ; zn , 50  mg ; fe , 80  mg ; cu , 5  mg ; se , 0.1  mg ; i , 0.18  mg 
 vitamins mix supplied per kilogram diet : vitamin a , 18,000  iu ; vitamin d3 , 4000  iu ; vitamin e , 36  mg ; vitamin k3 , 4  mg ; vitamin b12 , 0.03  mg ; thiamine , 1.8  mg ; riboflavin , 13.2  mg ; pyridoxine , 6  mg ; niacin , 60  mg ; calcium pantothenate , 20  mg ; folic acid , 2  mg ; biotin , 0.2  mg ; choline chloride , 500  mg percentage inclusion and calculated composition of diets 
 mineral mix supplied per kilogram diet : mn , 55  mg ; zn , 50  mg ; fe , 80  mg ; cu , 5  mg ; se , 0.1  mg ; i , 0.18  mg 
 vitamins mix supplied per kilogram diet : vitamin a , 18,000  iu ; vitamin d3 , 4000  iu ; vitamin e , 36  mg ; vitamin k3 , 4  mg ; vitamin b12 , 0.03  mg ; thiamine , 1.8  mg ; riboflavin , 13.2  mg ; pyridoxine , 6  mg ; niacin , 60  mg ; calcium pantothenate , 20  mg ; folic acid , 2  mg ; biotin , 0.2  mg ; choline chloride , 500  mg the effects of six experimental treatments consisting supplementation of drinking water with 0 ( control ) , 200 , 300 , 400 , and 500  mg / l skeo or 500  mg / l polysorbate 80 ( control ) were examined in six replicates of 20 birds each . polysorbate 80 used as an emulsifying agent to disperse skeo in water at a 1:1 ratio ( v / v ) . body weight gain , fi , and wi were measured weekly , and their data were used to calculate data on fcr and fi : wi ratio and a european broiler index ( ebi ) as ( euribrid 1994);\documentclass[12pt]{minimal } 
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				 \begin{document}$$ \mathrm{e}\mathrm{b}\mathrm{i}=\left(\mathrm{viability},\ \% \times \mathrm{live}\ \mathrm{weight},\ \mathrm{kg}\right)\times 100/\left(\mathrm{age}\ \mathrm{of}\ \mathrm{slaughtering},\ \mathrm{days } \times \mathrm{feed}\ \mathrm{intake},\ \mathrm{kg}\right ) $ $ \end{document}ebi = viability,%liveweight , kg100/ageofslaughtering , daysfeedintake , kg at day 21 of age , one male bird and at 42  days of age eight birds ( 4 males and 4 females ) from each replicate pen were killed ( without stunning ) by slicing the carotid artery and jugular vein , bled for 120  s , scaled at 60  c for 90  s , and picked using a rotary drum picker individually and eviscerated . after evisceration , the carcasses were individually weighed ( cw ) and the data were presented as a percentage of live weight ( cy ) . the weight of abdominal fat ( af ) , liver , pancreas , duodenum , and gall bladder were also expressed proportional to carcass weight . the aerial parts of s. khuzistanica were manually harvested during the flowering stage of the plant in khorraman farm , khorramabad , iran.1 the collected materials were air dried at ambient temperature under shade and hydrodistilled using a clevenger - type apparatus for 5  h , giving a yellow oil in 3  % yield . a sample of the bulk was analyzed based on the methods used by hadian et al . ( 2011 ) and the composition is presented in table  1.table 1essential oil composition of satureja khuzistanica 
 compoundri1composition ( % ) 
 -thujene9250.24    0.14 
 -pinene9330.15    0.05myrcene9810.26    0.19 
 -terpinene10130.24    0.12 
 p - cymene10171.26    0.86limonene10260.13    0.04(z)--ocimene10360.54    0.08 
 -terienene10530.74    0.23 
 trans - sabinene hydrate10810.17    0.02terpinen-4-ol1163tr -terpinolene11750.42    0.45thymol1266trcarvacrol128292.16    0.46thymyl acetate1329tr 
 -caryophyllene14250.16    0.01 
 -humulene1427tr 
 -bisabolene1501tr 
 trans--bisabolene15220.10    0.01 
 ri1 retention indices determined relative to n - alkanes ( c6c24 ) on a db-5gc column , tr trace ( < 0.05  % ) essential oil composition of satureja khuzistanica 
 
 ri1 retention indices determined relative to n - alkanes ( c6c24 ) on a db-5gc column , tr trace ( < 0.05  % ) a total number of 720 1-day - old arian broiler chicks were obtained from a commercial hatchery and housed in a concrete floor , cross - ventilated windowless shed . the chicks were randomly assigned to 36 pens ( 100    180  cm ) arranged in six replicate blocks at flocking density of 12 birds per m. corn and soybean meal based diets and water were provided to the birds for ad libitum consumption throughout the experiment ( table 2 ) . the shed was equipped with wet pad - and - fan cooling system to reduce the ambient temperature . nonetheless , during days 21 to 42 of experiment , the average temperature during day and night hours ranged from 32 to 35 and 28 to 30  c , respectively . therefore , it was considered that the birds were exposed to seasonal extreme ambient temperature from day 21 of age onwards.table 2percentage inclusion and calculated composition of dietsingredient ( % ) prestarter , 17  daysstarter , 721  daygrower , 2235  daysfinisher , 3642  dayscorn53.0055.3557.0061.00soybean meal25.0023.1222.520.5fish meal7.005.004.003.00soybean oil4.004.004.005.00wheat3.504.003.502.50calcium carbonate2.002.002.002.00wheat bran2.502.003.003.00dicalcium phosphate2.002.002.002.00dl - methoinine0.200.200.200.20 
 l - lysine0.120.110.100.10common salt0.250.250.250.25mineral premix 
 0.500.500.500.50vitamin permix 
 0.750.650.550.50coccidiostat0.100.100.100.00calculated composition  me , mj / kg12.3912.0512.3512.52  crude protein , % 22.2421.1520.0217.63  calcium , % 1.101.031.001.01  available p , % 0.450.440.400.45  methionine , % 0.520.530.400.43  lysine , % 1.151.081.101.03 
 mineral mix supplied per kilogram diet : mn , 55  mg ; zn , 50  mg ; fe , 80  mg ; cu , 5  mg ; se , 0.1  mg ; i , 0.18  mg 
 vitamins mix supplied per kilogram diet : vitamin a , 18,000  iu ; vitamin d3 , 4000  iu ; vitamin e , 36  mg ; vitamin k3 , 4  mg ; vitamin b12 , 0.03  mg ; thiamine , 1.8  mg ; riboflavin , 13.2  mg ; pyridoxine , 6  mg ; niacin , 60  mg ; calcium pantothenate , 20  mg ; folic acid , 2  mg ; biotin , 0.2  mg ; choline chloride , 500  mg percentage inclusion and calculated composition of diets 
 mineral mix supplied per kilogram diet : mn , 55  mg ; zn , 50  mg ; fe , 80  mg ; cu , 5  mg ; se , 0.1  mg ; i , 0.18  mg 
 vitamins mix supplied per kilogram diet : vitamin a , 18,000  iu ; vitamin d3 , 4000  iu ; vitamin e , 36  mg ; vitamin k3 , 4  mg ; vitamin b12 , 0.03  mg ; thiamine , 1.8  mg ; riboflavin , 13.2  mg ; pyridoxine , 6  mg ; niacin , 60  mg ; calcium pantothenate , 20  mg ; folic acid , 2  mg ; biotin , 0.2  mg ; choline chloride , 500  mg the effects of six experimental treatments consisting supplementation of drinking water with 0 ( control ) , 200 , 300 , 400 , and 500  mg / l skeo or 500  mg / l polysorbate 80 ( control ) were examined in six replicates of 20 birds each . polysorbate 80 used as an emulsifying agent to disperse skeo in water at a 1:1 ratio ( v / v ) . body weight gain , fi , and wi were measured weekly , and their data were used to calculate data on fcr and fi : wi ratio and a european broiler index ( ebi ) as ( euribrid 1994);\documentclass[12pt]{minimal } 
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				 \begin{document}$$ \mathrm{e}\mathrm{b}\mathrm{i}=\left(\mathrm{viability},\ \% \times \mathrm{live}\ \mathrm{weight},\ \mathrm{kg}\right)\times 100/\left(\mathrm{age}\ \mathrm{of}\ \mathrm{slaughtering},\ \mathrm{days } \times \mathrm{feed}\ \mathrm{intake},\ \mathrm{kg}\right ) $ $ \end{document}ebi = viability,%liveweight , kg100/ageofslaughtering , daysfeedintake , kg at day 21 of age , one male bird and at 42  days of age eight birds ( 4 males and 4 females ) from each replicate pen were killed ( without stunning ) by slicing the carotid artery and jugular vein , bled for 120  s , scaled at 60  c for 90  s , and picked using a rotary drum picker individually and eviscerated . after evisceration , the carcasses were individually weighed ( cw ) and the data were presented as a percentage of live weight ( cy ) . the weight of abdominal fat ( af ) , liver , pancreas , duodenum , and gall bladder were also expressed proportional to carcass weight . the statistical model used to analyze the collected data was\documentclass[12pt]{minimal } 
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				 \begin{document}$$ { y}_{ijkl}=\mu + { \mathrm{skeo}}_i+{s}_j+{b}_k+{\varepsilon}_{\mathrm{ijkl } } , $ $ \end{document}yijkl=+skeoi+sj+bk+ijkl , where yijkl is the dependent variable ,  is the general mean , skeoi is the fixed effect of skeo ( i  =  6 ; controland 0 , 200 , 300 , 400 , 500  mg / l skeo ) , sj is the fixed effect of sex ( j  =  2 ) , bk is the random effect of block ( j  =  6 ; 1 , 2 , 3 , 4 , 5 , and 6 ) and ijkl is the residual error . for the variables evaluated at day 21 of age , the fixed effect of sex the lsd test was used for multiple treatment comparisons using the lsmeans statement of sas 9.1 ( 2002 ) with letter grouping obtained using the sas pdmix800 macro ( saxton 1998 ) . for the different statistical tests , significance was declared at p  <  0.05 . the reg procedure of sas 9.1 ( 2002 ) was used to provide regression models for assessment of relationship between skeo and water intake . orthogonal polynomial contrasts were applied to test the linear or quadratic nature of the response in variables concerned to the graded levels of skeo in drinking water ( sas institute 2002 ) . supplementing skeo at the levels of 200 and 500  mg / l in drinking water did not change  average daily gain ( adg ) of the birds with the single  exception  of  days 29 to 35 of age when  adg was greater in skeo - received  birds  compared with the control birds ( p  <  0.05 ; table  3 ) . feed intake was similar among the birds ( p  >  0.05 ; table  4 ) . feed conversion ratio tended to be lower ( 3.5  % ) in the birds receiving 400  mg / l skeo than in the other birds ( p  =  0.058 ; table  4).table 3effect of essential oils of satureja khuzistanica on average daily weight gain in broiler chicken up to 42  days of ageweight gain ( g)essential oils of s. khuzistanica ( mg / l)sem 

 p valuecontrol 
 control 
 20030040050017  days16.6116.9016.7816.9116.9216.980.090.7981814  days26.2926.4126.2626.2127.1725.310.290.55471521  days41.3141.7240.1941.5239.4040.900.320.14842228  days72.6274.7276.0573.4874.9174.480.460.35902935  days81.36 
 87.72 
 87.48 
 80.00 
 85.00 
 80.29 0.870.00763642  days82.4381.4379.6085.6286.0783.001.250.6865142  days53.4354.8154.3953.9655.9153.490.230.2456means within a row without a common superscript ( a , b ) differ significantly ( p  <  0.05 ) 
 control : the birds that received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial . control : the birds that received drinking water with no additive 
 standard error of meantable 4effect of essential oils of satureja khuzistanica on average daily feed intake and feed conversion ratio in broiler chicken up to day 42 of agecontrol 
 essential oils of s. khuzistanica ( mg / l)trend0200300400500sem 

 p valuelinearquadraticfeed intake ( g )  17  days19.2619.6719.4019.0219.1919.530.1040.41580.23450.2013  814  days36.6236.1736.4537.0136.5036.290.1140.22580.65710.7201  1521  days60.0160.9560.0360.7159.8661.460.2520.31290.53210.1234  2228  days136.58132.36133.27132.07132.17129.780.8980.25110.45610.23402935  days183.41175.65176.13175.15175.41175.521.6030.67420.29130.45213642  days189.77199.85204.82210.97196.04214.242.7540.06720.39120.1219142  days104.27104.11105.08105.82103.18106.140.4660.43560.23450.0912feed conversion ratio ( g feed : g gain )  17  days1.1411.1851.1581.1251.1351.1510.0070.16030.20480.4193  814  days1.3931.3771.4081.4181.3511.4370.0140.51440.28340.2006  1521  day1.4401.4771.4941.4661.5231.5040.0100.12800.28170.3510  2228  days1.8291.8241.7541.7981.7651.7450.0130.16520.34610.41232935  days2.0992.1602.0222.1922.0662.1910.0260.31710.31160.42183642  days2.3692.4302.5922.4652.2782.5990.0420.18010.47600.1812142  days1.9031.9481.9301.9631.8801.9850.0110.05810.18230.1456 
 control 
 : the birds received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial 
 standard error of mean effect of essential oils of satureja khuzistanica on average daily weight gain in broiler chicken up to 42  days of age means within a row without a common superscript ( a , b ) differ significantly ( p  <  0.05 ) 
 control : the birds that received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial . control : the birds that received drinking water with no additive 
 standard error of mean effect of essential oils of satureja khuzistanica on average daily feed intake and feed conversion ratio in broiler chicken up to day 42 of age 
 control 
 : the birds received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial 
 standard error of mean water intake was significantly decreased by addition of skeo into drinking water in a dose - dependent manner during all weekly periods of age ( p  <  0.05 ; table  5 ) . supplementation of drinking water with skeo linearly decreased water intake from day 1 to 42 of age ( fig .  1 ) . a dose - response decrease was also observed in mean fi : wi ratio for all birds received skeo in their drinking water , but the response was not as much consistent as it was for wi ( p  <  0.01 ; table  5 ) . the mean mortality rate was not different for the treated birds compared to the control birds during days 1 to 21 and 22 to 42 of age ( p  >  0.05 ; fig .  2 ) . however , for pooled data overall periods , supplementation of drinking water with 300 and 500  mg / l skeo increased mortality rate of the birds mainly in the second episode of the growing period when the birds were under heat stress.table 5effect of essential oils of satureja khuzistanica on water intake and water : feed ratio in broiler chicks up to 28  days of agecontrol 
 essential oils of s. khuzistanica ( mg / l)trends0200300400500sem 

 pvaluelinearquadraticwater intake ( ml / day per bird )  17  days32.86 
 32.86 
 30.29 30.00 
 28.57 
 27.14 
 0.3530.00010.02340.5691  814  days97.14 
 102.86 
 94.29 
 95.71 
 92.86 
 91.43 
 0.6230.00010.00230.3491  1521 day162.86 
 161.43 
 177.14 
 167.14 
 167.14 
 154.29 
 1.1720.00010.00210.4001  2228  days249.00 
 257.43 
 238.86 
 242.57 
 218.57 
 215.71 2.5720.00010.00380.7412  2935  days322.07 
 297.09 
 305.19 
 278.64 
 271.43 
 257.14 3.6850.00010.02310.4183  3642  days351.00 
 328.43 
 328.71 
 314.14 
 300.00 
 281.71 3.7580.00010.00520.3426  142  days202.49 
 196.68 
 195.75 
 188.03 
 179.76 
 171.24 
 1.8100.00010.00100.7250water ( ml ) : feed ( g ) ratio  17  days1.71 
 1.67 
 1.56 
 1.58 
 1.49 
 1.39 
 0.0200.00010.01240.5791  814  days2.65 
 2.84 
 2.56 
 2.59 
 2.54 
 2.52 
 0.0200.00010.01830.2471  1521  days2.71 
 2.65 
 2.95 
 2.76 
 2.79 
 2.51 
 0.0250.00010.02510.4021  2228  days1.82 
 1.95 
 1.79 
 1.84 
 1.65 
 1.67 
 0.0210.00010.00280.6412  2935  days1.76 
 1.69 
 1.74 
 1.60 
 1.55 
 1.47 
 0.0230.00010.00490.2103  3642  days1.85 
 1.68 
 1.62 
 1.50 
 1.54 
 1.32 
 0.0320.00010.01310.4416  142  days1.94 
 1.89 
 1.86 
 1.78 
 1.75 
 1.61 
 0.0200.00010.02170.6270 
 control+ : the birds that received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial . control 
 : the birds that received drinking water with no additive 
 standard error for overall meanmeans within a row without a common superscript ( a  f ) differ significantly ( p  <  0.05)fig . 1effect of satureja khuzestanica essential oils ( skeo ) on water intake ( wi ) in broiler chicks during days 1 to 42 of age . means without a common superscript ( a  e ) differ significantly ( p  <  0.05)fig . 2effect of essential oils of satureja khuzistanica ( skeo ) on mortality of broiler chickens during 1 to 21 and 22 to 42  days of age . the letters inside the columns represent significant difference for mortality percent among treatments for 1 to 42  days of age . . means without a common superscript ( a  b ) differ significantly ( p  <  0.05 ) effect of essential oils of satureja khuzistanica on water intake and water : feed ratio in broiler chicks up to 28  days of age 
 control+ : the birds that received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial . control 
 : the birds that received drinking water with no additive 
 standard error for overall mean means within a row without a common superscript ( a  f ) differ significantly ( p  <  0.05 ) effect of satureja khuzestanica essential oils ( skeo ) on water intake ( wi ) in broiler chicks during days 1 to 42 of age . means without a common superscript ( a  e ) differ significantly ( p  <  0.05 ) effect of essential oils of satureja khuzistanica ( skeo ) on mortality of broiler chickens during 1 to 21 and 22 to 42  days of age . the letters inside the columns represent significant difference for mortality percent among treatments for 1 to 42  days of age . . means without a common superscript ( a  b ) differ significantly ( p  <  0.05 ) the calculated european broiler index was greater for the birds that received 400  mg / l of skeo in their drinking water compared to the other groups ( fig . there were no significant effects of skeo - treated water on carcass weight , carcass yield , and abdominal fat percentage in male and female birds at day 42 of age ( p  >  0.05 ; table  6 ) . the mean duodenum weight in days 21 and 42 of age was not affected ( p  >  0.05 ) by skeo - treated water ( table 7 ) . pancreas percentage was significantly increased ( p  <  0.05 ) for the birds that received 200 to 500  mg / l skeo at 21 and 42  days of age compared with that of the control groups . liver percentage ( as the percentage of carcass weight ) was not significantly different among the treated and control birds at day 42 of age ( p  <  0.05 ) . the relative weight of gall bladder was greater for the birds that received 500  mg / l skeo compared to the control birds at day 42 of age ( p  <  0.05 ; table 7).fig . 3effect of essential oils of satureja khuzistanica ( skeo ) on average european broiler index in broiler chicks at 42  days of age . means without a common superscript ( a  b ) differ significantly ( p  <  0.05)table 6effect of essential oils of satureja khuzistanica on carcass weight ( cw ; g ) , carcass yield ( cy ; % ) , abdominal fat - to - carcass weight ratio ( af : cw ) in broiler chicks at 42  days of agecwcyaf : cwmales  control 
 1662.640.542.442  01594.231.691.969  2001651.038.002.294  3001661.335.502.131  4001652.232.001.940  5001683.638.752.300  sem 
 14.4491.2020.067 
 p  <  f 
 0.15810.18590.2125trendslinear0.45100.28710 . 4511quadratic0.26720.32120.1873females  control 
 1408.041.772.970  01454.236.582.500  2001413.645.003.127  3001328.438.082.866  4001398.237.922.722  5001409.636.252.557  sem 
 15.2381.2030.077 
 p  <  f 
 0.29360.29100.1581trendslinear0.33210.38700 . 6517quadratic0.36420.39120.1271 
 control 
 : the birds received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial 
 standard error of meantable 7effect of essential oils of satureja khuzistanica on relative weight of duodenum and pancreas ( at 21 and 42  days ) and relative weight of liver and bile bladder ( at 42  day ) in broiler chickenscontrol 
 essential oils of s. khuzistanica ( mg / l)sem 

 p valuetrends0200300400500linearquadraticgram per 100  g body weight at 21  daysduodenum1.4121.6891.6281.6251.4831.5070.0450.31200.20720.1176pancreas0.549 
 0.492 
 0.579 
 0.547 
 0.528 
 0.545 
 0.0120.01920.35190.0172gram per 100  g body weight at 42  daysduodenum1.1801.2181.2691.3561.2231.1780.0230.19270.34510.2431pancreas0.332 
 0.302 
 0.332 
 0.329 
 0.332 
 0.340 
 0.0060.01210.03450.3391liver3.7833.6393.8313.5663.5833.5000.0650.66700.51000.4310gall bladder0.094 
 0.074 
 0.087 
 0.104 
 0.083 0.102 
 0.0040.01460.03410.1021 
 control 
 : the birds received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial 
 standard error of meanmeans within a column without a common superscript ( a  b ) differ significantly ( p  <  0.05 ) effect of essential oils of satureja khuzistanica ( skeo ) on average european broiler index in broiler chicks at 42  days of age . means without a common superscript ( a  b ) differ significantly ( p  <  0.05 ) effect of essential oils of satureja khuzistanica on carcass weight ( cw ; g ) , carcass yield ( cy ; % ) , abdominal fat - to - carcass weight ratio ( af : cw ) in broiler chicks at 42  days of age 
 control 
 : the birds received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial 
 standard error of mean effect of essential oils of satureja khuzistanica on relative weight of duodenum and pancreas ( at 21 and 42  days ) and relative weight of liver and bile bladder ( at 42  day ) in broiler chickens 
 control 
 : the birds received drinking water supplemented with 500  mg / l polysorbate 80 throughout the trial 
 standard error of mean means within a column without a common superscript ( a  b ) differ significantly ( p  <  0.05 ) in this study , skeo exhibited no promising effect on dwg of the broiler chicken through day 28 of age when the birds were maintained under normal production practices . however , in days 29 to 35 , when the birds suffered from an extreme heat stress episode , skeo - added water decreased dwg of the birds . the decreased dwg was mainly attributed to the lowered water intake which imposed a great challenge to the birds because they needed to drink more water to overcome their disturbed homeothermic state ( lara and rostagno 2013 ) . in a study , supplementation of drinking water with high doses of skeo ( ranging from 500 to 2500  mg / l ) adversely affected production performance of broiler chickens from days 1 to 28 of age ( khosravinia et al . 2013 ) . when the dose of skeo in drinking water were reduced below 500 mg / l , the birds received 500  mg / l skeo in the first 28  days of age compensated their weight gain afterwards . ( 2003 ) who reported a 2  % increase in average daily gain of broiler chicken by inclusion of 0.2  g per kg carvacrol in the diet . addition of tymole , an isomer of carvacrol , at the same dose caused a 3  % decrease in adg ( lee et al . however , the differences in the results could be explained by physiological status of the birds . in the current study , birds were not raised in standard conditions . the inconsistency in the results of current study with those reported by the other researchers could be also explained by the fact that in this experiment skeo was added to the drinking water , while in the other studies the active components of skeo ( such as carvacrol ) were mainly included in the diet . in agreement with the findings of the current study , ( 2004 ) reported that dietary oregano extract ( a natural product rich in carvacrol ) at 0.15 g / kg decreased adg in broiler chicken by 2  % compared to the control birds . however , when the applied dose doubled ( 0.3  g / kg ) , adg was increased as much as 2  % compared to the control group . therefore , no dose - dependent or an age - associated response could be pointed out . the unchanged fi for the treated birds was in agreement with the findings of lee et al . the later researchers found that dietary inclusion of 0.2  g / kg carvacrol and 0.15  g / kg oregano extract caused 2  % increase and 6  % decrease in fi of the birds compared with the relevant control groups , respectively . in contrast to the published results , in this study , adding skeo into drinking water had no effect on fcr . ( 2012 ) who reported decreased fcr for the birds fed with diets containing carvacrol or carvacrol - rich essential oils . the inconsistencies observed in the findings of different experiments may be attributed to the differences in management practices applied in the experimental flocks and physiological state of the birds . in the present study , such effect has been already assigned to the flavor of water ( khosravinia et al . the bitter and pungent taste of carvacrol and possibly other principle components of skeo caused a significant drop in water intake . water is involved in every aspect of broiler metabolism , playing important roles in regulating body temperature , digesting food , and eliminating body wastes . at normal temperatures , poultry consume at least twice as much water as feed . under heat stress , water intake increases ( quinteiro - filho et al . it seems that the caustic taste of water did not allow the treated birds to increase their wi when they were exposed to heat stress . therefore , a dose - dependent decrease in mean fi : wi ratio was observed ( fig .  1 ) . unfortunately , effects of flavors on chicken performance have not been investigated in detail . because , most researchers believe that broilers may not actually respond to the flavors as compared with mammals ( moran 1982 ) . it was shown that dietary inclusion of carvacrol in broiler chicks reduced feed intake by modulating appetite of the birds ( lee et al . ( 2004 ) , findings of the present study also questioned the assumption that phytogenic extracts improve the palatability of diet ( windisch et al . the great attention currently focused on administration of essential oils and other phytogenic products to poultry urges further investigation on response of avian species to flavors in water and feeds . it is usually greater in broiler flocks exposed to extreme environmental temperatures compared to those maintained in normal conditions . water intake is an important determinant in mortality rate in heat - stressed birds ( bruno et al . water intake increases in heat - stressed birds to maintain thermoregulatory balance ( bruno and macari 2002 ) , because heat stress increases water loss via exhalation as a mean to cool down body temperature ( zhang et al . , it was speculated that the decreased water intake was due to the bitter taste of carvacrol resulted in greater mortality rates in treated birds . such a speculation became a reality as the mortality rate increased in the birds received 300 and 500  mg / l skeo when they were exposed to extreme ambient temperature in days 21 to 42 of age . researchers have tried to pool the fractional influence of many production criteria in an index to compare performance of different flocks . the index created by euribrid ( 1994 ) is calculated based on final body weight , fcr , and mortality . the calculated index for the treated birds with 400  mg / l of skeo through drinking water was greater compared to other groups . the diminutive advantages of water treated with 400  mg / l skeo in dwg , improved fcr in days 1 to 42 of age and lowered mortality rate especially during days 22 to 42 of age was reflected as an improved ebi index . these results suggest that 400  mg / l can be recommended as the dose for addition of skeo into drinking water for broiler chickens . in the current study , cw and cy these results were expected as carcass weight is mainly associated with pre - slaughter weight but carcass yield is mainly correlated to body composition among many other factors . however , it was anticipated that skeo exerts a considerable impact on abdominal fat percentage . ( 1995 ) reported that dietary inclusion of carvacrol affected fat metabolism in broiler chicken as shown by decreased abdominal fat ( af ) . in broiler chicken , lipids and triglycerides in particular there is a general postulation that almost all the fat built up in broiler adipose tissue including abdominal fat is synthesized in the liver or derived from the diet ( griffin et al . ( 2013 ) who reported that supplementation of drinking water with skeo ( 500 to 2500  mg / l ) significantly reduced abdominal fat in both male and female birds raised under normal conditions . in conclusion , the present study revealed that administration of skeo at 400  mg / l through drinking water to heat - stressed broiler chickens improves economic efficiency of broiler flocks possibly through promoting the digestion process , creating minute improvement in fcr and lowered mortality rate .
an experiment was conducted to examine the effects on mortality , production performance , water intake ( wi ) , and organ weight of satureja khuzistanica essential oil ( skeo ) using 720 1-day - old arian broiler chicks in a 42-day trial . 
 experimental treatments were addition of 0 ( control ) , 200 , 300 , 400 , and 500  mg / l skeo or 500  mg / l polysorbate 80 ( control+ ) into drinking water . 
 the birds were kept under natural ambient temperatures 4 to 6  c above standard recommendation from days 22 to 42 of age . 
 addition of skeo into drinking water at 200 and 500  mg / l decreased weight gain ( p  <  0.05 ) of the birds from days 29 to 35 of age with no differences in feed intake ( fi ) and feed conversion ratio ( fcr ) compared to control groups ( p  >  0.05 ) . 
 supplementation of drinking water with 200 , 300 , 400 , and 500  mg / l skeo resulted in a 0.47 , 4.40 , 8.60 , and 12.93  % decrease in wi , respectively , from days 1 to 42 of age . 
 the calculated european broiler index was greater for the birds received 400  mg / l of skeo in their drinking water compared with that of the other birds ( p  <  0.05 ) . 
 pancreas percentage was increased for the birds received 200 to 500  mg / l skeo at days 21 and 42 of age compared with that of the control birds ( p  <  0.05 ) . 
 the gall bladder weight was 17.56 , 40.50 , 12.16 , and 38.73  % greater for the birds received 200 , 300 , 400 , and 500  mg / l skeo compared with that of the control birds , respectively . 
 the results showed that an addition of 400  mg / l skeo into drinking water for heat - stressed broiler chickens improves economic efficiency possibly by promoting digestion process , creating miniscule improvement in fcr and lowered mortality rate .