Evaluating the Relationship Between Environment and Body Temperature of Hair Sheep Ewes in the Tropics

The objective of this study was to evaluate the relationship between environment and body temperature in tropically adapted hair sheep ewes while grazing on pasture. Non-pregnant, non-lactating, multiparous St. Croix White (STX, 5.6 y of age, 43 kg, n = 5) and Dorper x St Croix White (DRPX, 3.8 y of age, 43 kg, n = 5) ewes were evaluated for 96 h d each mo for 1 yr. Temperature data loggers recorded vaginal temperature (VT) at 10-min intervals during ecah 96-h period. Ambient temparture (TEMP), relative humidity (RH), solar radiation (SOLAR) and THI were measured during the data collections using an onsite weather station (Davis Instruments, Oakland, CA). Data were analyzed using GLM procedures of SAS with breed, time of year and time of day in the model. Over the entire year mean TEMP, RH, THI and SOLAR were 27.1 °C, 79.0 %, 77.9 and 255 W/m², respectively. The DRPX ewes had a higher VT than STX ewes between 0900 and 1900 h and 2100 through 0300 h (P < 0.0001). There was no difference in VT during 0400 to 0800 h (P > 0.10). The minimum VT during the day was not different (P > 0.10) between DRPX and STX ewes (38.47 ± 0.07 vs. 38.42 ± 0.06 °C, respectively). The DRPX ewes had a greater maximum VT (P < 0.0001; 39.58 ± 0.02 vs. 39.37 ± 0.02 °C, respectively) and range of VT (P < 0.06; 1.12 ± 0.07 vs. 0.95 ± 0.06 °C, respectively) than STX ewes did. In STX ewes there was no difference in VT during the afternoon (1300 to 1900 h) during the evening (1900 to 2400 h; P > 0.10; 39.08 ± 0.01). In DRPX ewes VT during the afternoon was greater than VT during the evening (P < 0.0001; 39.29 ± 0.01 vs. 39.13 ± 0.01 °C, respectively). In DRPX and STX ewes VT was lowly correlated with TEMP measured at 1 h prior (r = 0.28 and r = 0.31, respectively; P< 0.0001). In DRPX and STX ewes VT was lowly correlated with SOLAR measured at 1 h prior (r = 0.13 and r = 0.07, respectively; P< 0.0001). The lower VT of STX ewes compared to that of DRPX ewes is likely due to their adaptation to the high heat and humidity found in the tropics.