the animal experimentation protocol was approved by the president of kitasato university with a judgment of the institutional animal care and use committee of kitasato university . bst was measured as follows : a temperature sensor with a data logger ( kestrel drop d1 ; kestrel meters , sylvan lake , mi , usa ) was placed in close contact with the skin on the upper neck of each test ewe , fixed by tying it with the 
 ewe s fur , and covered with fur so that the sensor was not exposed to ambient air ( fig . the body surface temperature sensor ( a ) was placed in close contact with the skin on the upper neck of the ewe ( b ) , fixed by tying it with the ewe s fur , and covered with fur so that the sensor was not exposed to the ambient 
 air ( c ) . a small temperature sensor with a data logger for the measurement of vaginal temperature was embedded in a sponge ( d , e ) . ) . showed that this method has 
 potential as a monitoring system for bst in cattle by infrared thermography temperature collection at different body locations ( i.e. , the eye , back of the ear , shoulder , and vulva ) . however , when the temperature sensor was used to 
 measure bst , it was necessary to attach the sensor on the outside of the ewe s body in a place from which an ewe could not remove the sensor . the body surface temperature sensor ( a ) was placed in close contact with the skin on the upper neck of the ewe ( b ) , fixed by tying it with the ewe s fur , and covered with fur so that the sensor was not exposed to the ambient 
 air ( c ) . a small temperature sensor with a data logger for the measurement of vaginal temperature was embedded in a sponge ( d , e ) . vaginal temperature ( vt ) was used to assess the core body temperature . a small temperature sensor with a data logger ( thermocron sl , kn laboratories , osaka , japan ) was embedded in a sponge , placed in the vagina of each test ewe , 
 and set to record vt every 10 min . after the completion of the measurement , the sponge was removed from the vagina and the measurement data was retrieved in the same way as for bst . ambient temperature ( at ) in the barn was also measured throughout the study period using a temperature sensor with a data logger ( kestrel drop d1 ; kestrel meters ) . at was recorded every 10 min and the atmospheric temperature of the 
 height was the same as that of the ewes in the barn . the barn was naturally ventilated and lights were on from 0830 to 1730 h jst . to enable filming with light - sensitive cameras during the dark period , four non - pregnant adult corriedale ewes ( 25.2  20.7 months old , 45.9  1.5 kg bw ) were used in this experiment in spring . the animals were housed individually in 
 stainless steel cages 86 cm wide  136 cm long with a raised wooden slatted floor ( height : 30 cm ) in the barn . the 
 animals were fed the necessary amount of roughage and concentrated feeds calculated on the basis of each test ewe s body weight according to the japanese feeding standard for sheep . the 
 feed was divided into two doses : one in the morning ( 0830 h ) and one in the late afternoon ( 1630 h ) . the animals had access to water and rock salt ad libitum . after seven days , the bst of the upper neck , vt , and 
 at were collected and analyzed . seven pregnant corriedale ewes ( 38.9  0.3 months old , 52.0  7.7 kg bw ) in their third trimester were used in this experiment and housed individually in cages ( 86 cm 
 wide  136 cm long ) . the test ewes were continuously monitored by a web camera to accurately determine the time of parturition . bst was recorded every 10 min , 
 starting three days before the expected date of parturition and continuing until the end of parturition , using the aforementioned procedure . at the end of the study , the measurement data were retrieved and analyzed to calculate 
 the hourly averages of bst during the 72 h before parturition . pearson s correlation coefficient was used to calculate bst , vt , and at correlations . bst measurements several days before parturition were compared using tukey - kramer s multiple comparison test . using dunnett s test , prepartum 
 hourly bst measurements were compared with measurements between 72 h and 69 h before parturition as the control . all statistical analyses were performed using jmp 8.0.1 software ( jmp version 8.01 ; sas institute , cary , nc , usa ) . four non - pregnant adult corriedale ewes ( 25.2  20.7 months old , 45.9  1.5 kg bw ) were used in this experiment in spring . the animals were housed individually in 
 stainless steel cages 86 cm wide  136 cm long with a raised wooden slatted floor ( height : 30 cm ) in the barn . the 
 animals were fed the necessary amount of roughage and concentrated feeds calculated on the basis of each test ewe s body weight according to the japanese feeding standard for sheep . the 
 feed was divided into two doses : one in the morning ( 0830 h ) and one in the late afternoon ( 1630 h ) . after seven days , the bst of the upper neck , vt , and 
 at were collected and analyzed . seven pregnant corriedale ewes ( 38.9  0.3 months old , 52.0  7.7 kg bw ) in their third trimester were used in this experiment and housed individually in cages ( 86 cm 
 wide  136 cm long ) . the test ewes were continuously monitored by a web camera to accurately determine the time of parturition . bst was recorded every 10 min , 
 starting three days before the expected date of parturition and continuing until the end of parturition , using the aforementioned procedure . at the end of the study , the measurement data were retrieved and analyzed to calculate 
 the hourly averages of bst during the 72 h before parturition . pearson s correlation coefficient was used to calculate bst , vt , and at correlations . bst measurements several days before parturition were compared using tukey - kramer s multiple comparison test . using dunnett s test , prepartum 
 hourly bst measurements were compared with measurements between 72 h and 69 h before parturition as the control . all statistical analyses were performed using jmp 8.0.1 software ( jmp version 8.01 ; sas institute , cary , nc , usa ) . 
 differences were considered to be significant at p < 0.05 . the mean (  sd ) at during the study period was 16.5  3.9c ( ranging from 9.0 to 26.4c ) . the mean ewe s bst and vt during the study period were 35.4  1.7c and 39.1  0.4c , respectively , with a correlation between bst and vt 
 of r = 0.62 ( p < 0.001 ; fig . 2 . the relationship between vaginal and body surface temperatures in ewes ( n = 4 ) . ) . the correlations between at and bst and between at and vt were r = 0.26 ( p < 0.001 ) and r = 0.28 ( p < 0.001 ) , respectively . the relationship between vaginal and body surface temperatures in ewes ( n = 4 ) . body surface temperature ( mean  sd ) of ewes ( n = 7 ) 72 h before lambingtime before lambing ( h)body surface temperature ( c)72 4835.4  1.5 48 2435.2  1.4 24 034.7  1.3   denotes significantly different means ( p < 0.05 ) . shows the comparison of the mean bst measurements at 72 48 h , 48 24 h , and 240 h ( 0 h = time of parturition ) . the mean bst at 240 h was significantly lower than that at 48 24 h ( 0.5c ) and 72 48 h 
 ( 0.7c ) ( changes in body surface temperature ( mean  sd ) in ewes ( n = 7 ) during 72 h before parturition . relative changes in body surface temperature when the temperature was 72 h ( 0 h = time of parturition ) is set at 0 . * 
 indicates a significant difference compared to the value at 72 h ( p < 0.05 ) . shows the change in bst measurements during the 72 h before parturition compared with the measurements at 72 h. the bst tended to decrease with measurements that were taken closer to parturition ; a continuous decrease in 
 bst was observed in 27 3 h. in addition , measurements at 16 3 h were significantly lower than those at 72 h ( p < 0.05 ) . the mean bst measurements at 16 3 h was 1.1c ( ranging from 0.93 to 1.27c ) lower than those at 
 72 h. in contrast , the bst increased at 20 h.   changes in body surface temperature ( mean  sd ) in ewes ( n = 7 ) during 72 h before parturition . * 
 indicates a significant difference compared to the value at 72 h ( p < 0.05 ) . the difference between the body surface temperature ( mean  sd ) in ewes ( n = 7 ) at a particular time of the day and at the same time on the preceding day . shows the difference between the bst at a particular time of the day and at the same time on the preceding day . a decrease in bst of 0.2 to 0.7c between a particular time of day and the same time of the preceding day was 
 observed at 33 3 h.   the difference between the body surface temperature ( mean  sd ) in ewes ( n = 7 ) at a particular time of the day and at the same time on the preceding day . 5 . a comparison of the diurnal rhythm of the body surface temperature in ewes ( n = 7 ) for day 2 , day 1 , and day 0 ( day 0 = day of parturition ) . data for day 2 , day 1 and day 0 body 
 surface temperature are presented as the mean  sd . sd  1.25 , 1.29 , and 1.40 for day 2 , day 1 , and day 0 , respectively . shows the diurnal variation in bst between 0000 and 2300 h on day 2 , day 1 , and day 0 ( day 0 = day of parturition ) . on day 2 and day 1 , a clear circadian rhythm in bst was observed whereby the temperature was low in the 
 morning and high in the late afternoon and during the night , and increased after feeding ( 0830 , 1630 h ) , with a smaller magnitude of variation on day 1 . on day 0 , a clearly different pattern of diurnal variation than those 
 observed during the two preceding days was observed , showing an unclear circadian rhythm .   a comparison of the diurnal rhythm of the body surface temperature in ewes ( n = 7 ) for day 2 , day 1 , and day 0 ( day 0 = day of parturition ) . data for day 2 , day 1 and day 0 body 
 surface temperature are presented as the mean  sd . sd  1.25 , 1.29 , and 1.40 for day 2 , day 1 , and day 0 , respectively . the mean (  sd ) at during the study period was 16.5  3.9c ( ranging from 9.0 to 26.4c ) . the mean ewe s bst and vt during the study period were 35.4  1.7c and 39.1  0.4c , respectively , with a correlation between bst and vt 
 of r = 0.62 ( p < 0.001 ; fig . 2 . the relationship between vaginal and body surface temperatures in ewes ( n = 4 ) . ) . the correlations between at and bst and between at and vt were r = 0.26 ( p < 0.001 ) and r = 0.28 ( p < 0.001 ) , respectively . the relationship between vaginal and body surface temperatures in ewes ( n = 4 ) . table 1table 1 . body surface temperature ( mean  sd ) of ewes ( n = 7 ) 72 h before lambingtime before lambing ( h)body surface temperature ( c)72 4835.4  1.5 48 2435.2  1.4 24 034.7  1.3   denotes significantly different means ( p < 0.05 ) . shows the comparison of the mean bst measurements at 72 48 h , 48 24 h , and 240 h ( 0 h = time of parturition ) . the mean bst at 240 h was significantly lower than that at 48 24 h ( 0.5c ) and 72 48 h 
 ( 0.7c ) ( p < 0.05 ) . changes in body surface temperature ( mean  sd ) in ewes ( n = 7 ) during 72 h before parturition . relative changes in body surface temperature when the temperature was 72 h ( 0 h = time of parturition ) is set at 0 . * 
 indicates a significant difference compared to the value at 72 h ( p < 0.05 ) . shows the change in bst measurements during the 72 h before parturition compared with the measurements at 72 h. the bst tended to decrease with measurements that were taken closer to parturition ; a continuous decrease in 
 bst was observed in 27 3 h. in addition , measurements at 16 3 h were significantly lower than those at 72 h ( p < 0.05 ) . the mean bst measurements at 16 3 h was 1.1c ( ranging from 0.93 to 1.27c ) lower than those at 
 72 h. in contrast , the bst increased at 20 h.   changes in body surface temperature ( mean  sd ) in ewes ( n = 7 ) during 72 h before parturition . relative changes in body surface temperature when the temperature was 72 h ( 0 h = time of parturition ) is set at 0 . * 
 indicates a significant difference compared to the value at 72 h ( p < 0.05 ) . the difference between the body surface temperature ( mean  sd ) in ewes ( n = 7 ) at a particular time of the day and at the same time on the preceding day . shows the difference between the bst at a particular time of the day and at the same time on the preceding day . a decrease in bst of 0.2 to 0.7c between a particular time of day and the same time of the preceding day was 
 observed at 33 3 h.   the difference between the body surface temperature ( mean  sd ) in ewes ( n = 7 ) at a particular time of the day and at the same time on the preceding day . 5 . a comparison of the diurnal rhythm of the body surface temperature in ewes ( n = 7 ) for day 2 , day 1 , and day 0 ( day 0 = day of parturition ) . data for day 2 , day 1 and day 0 body 
 surface temperature are presented as the mean  sd . sd  1.25 , 1.29 , and 1.40 for day 2 , day 1 , and day 0 , respectively . shows the diurnal variation in bst between 0000 and 2300 h on day 2 , day 1 , and day 0 ( day 0 = day of parturition ) . on day 2 and day 1 , a clear circadian rhythm in bst was observed whereby the temperature was low in the 
 morning and high in the late afternoon and during the night , and increased after feeding ( 0830 , 1630 h ) , with a smaller magnitude of variation on day 1 . on day 0 , a clearly different pattern of diurnal variation than those 
 observed during the two preceding days was observed , showing an unclear circadian rhythm .   a comparison of the diurnal rhythm of the body surface temperature in ewes ( n = 7 ) for day 2 , day 1 , and day 0 ( day 0 = day of parturition ) . data for day 2 , day 1 and day 0 body 
 surface temperature are presented as the mean  sd . sd  1.25 , 1.29 , and 1.40 for day 2 , day 1 , and day 0 , respectively . studies using holstein cattle have shown a good correlation between vaginal and rectal temperatures [ 24 , 25 ] . while it is difficult to place a short - term 
 internal temperature - measuring device in the rectum , the usefulness of vt measurements has been demonstrated for continuous monitoring of the core body temperature [ 26 , 27 ] . in this study , although the mean bst measured at the upper neck of ewes was lower than the mean vt by 3.7c , a significant correlation was observed between the two 
 parameters , suggesting that bst is associated with core body temperature . berry et al .   also observed a significant positive correlation between udder surface temperature 
 measured by infrared thermography and rectal temperature . although bst is considered to be affected by changes in at , the correlation between bst and at was comparable to that of vt and at 
 in this study . this may be because the temperature sensor was closely attached to the body surface at the upper neck of ewes and covered by the ewes fur . this observation demonstrates the validity of the method for measuring bst at 
 the upper neck . however , the present study was performed in mild weather conditions ( at ranged from 9.0 to 26.4c ) . hence , in severe hot or cold conditions , it is possible that the results would be different from those of this 
 study . the mean bst measurements at 240 h was significantly lower than those at 72 48 h and 48 24 h. similar results were reported in previous studies that measured vt in prepartum beef cattle   or vt and rectal temperature in holstein cattle . in the assessment of hourly incremental changes in bst over 72 h before parturition , a continuous decrease in bst was 
 observed at 27 3 h. in addition , a decrease in bst of 0.2 to 0.7c between a particular time of day and the same time of the preceding day was observed at 33 3 h. aoki et al . continuously measured vt of prepartum beef cattle and observed a consistent decrease in vt of  0.5c with respect to the temperature at the same time on the preceding day ( 29.7 h before parturition ) , which is 
 consistent with our data . pregnancy - related fluctuations in body temperature , such as increased body temperature during pregnancy   and a prepartum decrease in body temperature , have been associated with a change in the plasma concentration of progesterone secreted from the corpus luteum during pregnancy [ 32 , 33 ] . thus , the prepartum decrease in bst observed in this study was also likely 
 to reflect corpus luteum regression and a subsequent decrease in progesterone concentration . in addition , the mean bst measurements at 16 3 h were lower ( 1.1c ) than those at 72 h. it is possible to predict the time of 
 parturition by detecting this decrease . such an elevation in body temperature immediately before parturition has been previously reported [ 13 , 14 , 25 ] . although the precise cause of this phenomenon is unknown , it is likely associated with increased activity , such as frequent changes between standing 
 and lying during the first stage of labor . a circadian rhythm in body temperature , whereby temperature is low in the morning , high in the late afternoon until the night , and declines until the following morning , has been observed in cattle   and ewes . in addition , piccione et al .   confirmed that bst was lower than core body temperature , but exhibited 
 significant daily rhythmicity in sheep . in this study , a clear circadian rhythm in the bst was observed on day 2 and day 1 , although the magnitude of the diurnal variation was lesser on day 1 . moreover , a different pattern than 
 those observed during the two preceding days was observed on day 0 , showing an unclear circadian rhythm . lammoglia et al .   reported that the circadian rhythm of body temperature disappeared at 48 h before parturition in beef cattle . these observations support the results of 
 this study . in conclusion , this study showed that bst was continuously measured at the upper neck of ewes using a temperature sensor with a data logger was significantly correlated with vt , suggesting that bst is associated with core body 
 temperature . we also observed a marked decrease in bst at the upper neck in the prepartum period . a number of previous studies have shown prepartum decreases in vaginal and rectal temperatures in cattle [ 13 , 14 , 25 ] and in ewes , measured using invasive techniques . to the best of our knowledge , 
 there have been no previous reports on the prepartum decrease in bst further studies will be needed to clarify whether the prepartum decrease in bst varies 
 in a species - specific manner .
this study investigated the correlation between the body surface temperature ( bst ) and core body temperature of ewes and changes in bst during the prepartum stage in pregnant ewes . 
 four non - pregnant adult ewes were used in the 
 first experiment . 
 the bst of the upper neck , vaginal temperature ( vt ) , and ambient temperature ( at ) were measured every 10 min for seven days and analyzed for correlations . 
 the mean (  sd ) bst and vt of ewes during the study 
 period were 35.4  1.7c and 39.1  0.4c , respectively , with a correlation of r = 0.62 , p < 0.001 . 
 this finding suggested that the bst was associated with core body temperature in ewes . 
 in the subsequent experiment , seven 
 pregnant ewes in their third trimester were used to evaluate changes in bst measured at the upper neck 72 h before parturition . 
 the mean bst at 240 h ( 0 h = time of parturition ) was significantly lower than that at 72 48 h 
 and 48 24 h ( p < 0.05 ) . 
 the bst tended to decrease toward parturition ; all bst measurements at 16 3 h were significantly lower than those at 72 h ( p < 0.05 ) . 
 a clear circadian rhythm in the bst was observed at two 
 days and the day before parturition and an unclear circadian rhythm was observed on the day of parturition . 
 therefore , these findings indicate that the bst also decreases before parturition , as do vaginal and rectal 
 temperatures .