1179 The effect of vaginal temperature on expressed physical activity of lactating Holstein cows following induced estrus

Abstract

The objective of this study was to determine the effect of vaginal temperature on levels of physical activity expressed by lactating Holstein cows following induced estrus. Lactating Holstein cows (n = 641; 41.5 ± 9.4 kg milk/d) were fitted with a leg-mounted pedometer (AfiActII, Afimilk, Israel) resulting in 843 evaluated activity episodes of estrus. Vaginal temperature was monitored using thermometers (Thermochron iButton −40°C thru +85°C), attached to an intravaginal device (CIDR) as part of a timed-AI protocol (CIDR+estradiol benzoate+GnRH-7d-PGF-2d-CIDR out+PGF+ECP-2d-timed AI), which recorded vaginal temperature every 10 min for 3 d. Ambient temperature and relative humidity were monitored using an external thermometer placed in the center of each pen. Milk production and BCS were collected at time of thermometer insertion. All statistical analysis was performed in R and R Studio using GLM and ARM packages. Heat stress was calculated based on the percentage of time the cow spent with a vaginal temperature greater than 39.1°C (HS). The mean HS was 36.8 ± 24.5%, whereas the mean maximum (MaxVT) and minimum (MinVT) vaginal temperatures were 39.7 ± 0.5°C and 38.0 ± 0.8°C, respectively, with an average amplitude (AMP) 1.71 ± 0.9°C. Mean peak activity (PA) at estrus was 237.0 ± 160.0% relative increase. Increasing MaxVT negatively affected mean PA (ODDS = 0.67, P < 0.01). PA was significantly affected by parity as multiparous cows expressed lower PA compared to primiparous cows (ODDS = 0.76, P < 0.01). MinVT, AMP, and HS had no significant effects on mean PA, but cows displaying greater PA at estrus had greater P/AI compared with lower PA (28% vs. 18% P < 0.003). The P/AI at 32 d was significantly reduced by increasing MaxVT (ODDS = 0.67 P < 0.05); however HS, MinVT, and AMP did not significantly affect P/AI. Future research should aim to refine variables related to hyperthermia as well as further effects of body temperature on physical activity behaviors such as lying time, bout, rumination, and subsequent effects on estrous expression and pregnancy rates.