Factors affecting vaginal temperature in high producing lactating Holstein cows

The aim of this experiment was to evaluate the continuous collection of vaginal temperature for 72 h (every 10 min) in lactating Holstein cows (n= 480; 591 data collections of insemination) allocated in one single cross-ventilation barn. Cow were fitted with a thermometer attached to a progesterone intravaginal device (1.9g P4, CIDR, Zoetis) prior to timed artificial insemination (TAI). Milk production, DIM, skin thickness, coat color, body condition score (BCS), and pregnancy per AI (P/AI) data were collected and recorded for further analyses. Ambient temperature and humidity of barn was measured for 72 housing a data logger for calculation of the temperature and humidity index (THI). Data was analyzed using ANOVA and Pearson’s correlations using proc GLM, Corr and Logistic of SAS. Maximum THI (MAX) and percentage of time above a vaginal temperature of 39.1°C (PCT) were used as data logger responses, class variables were created for MAX and PCT (High vs. Low) using the median threshold. There was a low correlation between THI and PCT (P 50.7kg/d) spent more time with high vaginal temperatures. Among the independent variables included in the model, parity (P < 0.01), PCT (P = 0.03; 26.1 vs. 17.4% for Low and High, respectively) and a PCT by milk production interaction (P = 0.05) affected P/AI. The decrease in P/AI in cows with High PCT only occurred in cows with the highest production. In summary, there is a large variability in individual capacity of cows respond to heat stress. Parity, BCS, coat color and milk production affected PCT, particularly under high ambient temperatures. Selection of animals with efficient control of body temperature in spite of high milk production should be further approached as a strategy to maintain adequate fertility of dairy herds.