Ruminal Temperature for Identification and Prediction of Estrus in Beef Cows
Abstract
Postpartum, Angus cows were used to evaluate changes in ruminal temperature (RuT) for the identification and prediction of estrus. Cows were administered RuT transmitting boluses and synchronized with PGF2&alpha. Ruminal temperature and ambient temperature were recorded hourly. The onset of estrus was determined by HeatWatch. Estrus was determined as a RuT increase of &ge 0.7°C for a 9 h period compared with the mean RuT during the 12 to 84 h before the start of the 9 h period. Cows predicted as estrous based on RuT were AI to Angus bulls, 8 to 16 h after the first hour of the 9 h period in which RuT increased &ge 0.7°C. Ruminal temperature was evaluated during the 16 to 24 before and 24 to 32 h after the onset of estrus. The effect of ambient temperature (Tamb) on RuT was evaluated in postpartum, Angus cows. Cows were exposed to Tamb ranging from 12 to 37°C. Relationships among RuT, maximal Tamb (Tmax) and temperature humidity index (THI) were evaluated during 8 d in January, June, and August. Relationships between rectal temperature (RT), respiration rate (RR), Tmax, THI, and RuT were evaluated on two sequential days in August when Tmax was 37°C (HOT) and 28°C (WARM). Ruminal temperature was greater during the 9 h after the onset of estrus compared with the 16 to 24 h before and 24 to 32 h after the onset of estrus. Increased RuT at estrus occurred when onset of estrus was at 0100 to 0800, 0900 to 1600, 1700 to 0000 h. Time of day influenced RuT in the 9 h after the onset of estrus. Daily Tmax of &ge 32°C increased the magnitude of diurnal variation in RuT and influenced RuT at estrus compared with when ambient temperature was < 32°C. Correct identification of estrous cows by a RuT increase of &ge 0.7°C occurred in 61% to 93% of cows. Non estrous cows were identified as estrus by a RuT increase of &ge 0.7°C in 16 to 73 % of cows. Pregnancy rate of cows AI based on RuT was 40% or greater and was not influenced by daily Tmax. When cows were exposed to Tmax &ge 34°C or THI &ge 87, RuT was increased compared with Tmax < 34&geC or THI < 87, respectively. Ruminal temperature, RT, and RR were greater on the HOT day compared with the WARM day. Ruminal temperature was positively correlated with RT, RR, Tmax, and THI. These results indicate that the use of RuT has potential for estrous detection in cattle. Estrous detections systems that utilize changes in physiology are less subjective than visual observation of estrous behavior, require less time, and labor expense. A RuT based estrous detection system may increase the use of AI in the cow-calf industry. Insemination of cows to genetically superior bulls provides producers the opportunity to decrease the calving interval, increase the number and weight of calves, and enhance the profitability of a cowherd.
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- OSU Theses [15752]