Relationship among estradiol, cortisol and intensity of estrous behavior in dairy cattle

Economic profitability of a dairy farm is based, in part, on the calving in terval of the cows. The optimal interval is 365 d. To achieve this, the cow needs to be pregnant within 85 d post partum. The first and most problemat ic step in this process is the determination of the optimal time for insemi nation, which is based on estrous behavior. The expression of estrous behav ior, however, is at a low level in modem dairy herds, resulting in low dete ction rates and longer calving intervals. In the present study, a point sca le was used to monitor postpartum, nonpregnant cows for estrous symptoms. F requent blood samples were taken around estrus, and the cows were fit with pedometers to measure their activity. Correlations between the occurrence o f symptoms of estrus and levels of estradiol and cortisol were then analyze d. Standing heat, the standard symptom of estrus, was observed in only 53% of the cows. A high correlation of 0.7 was found between estradiol concentrati on and estrous behavior. This was empasized by the fact that the estradiol level reached its highest level of 7.76 + 2.39 (SD) pg/mL at the same time as the highest behavior score. The highest pedometer readout lagged 8 h beh ind this moment. Cortisol levels did not exceed the physiological levels in rest situations but showed an increase at the time estrous behavior was at its maximum. The present study showed that standing heat is not the primary symptom for detecting estrus in cows. Pedometers are a useful aid but they have to be r ead several times a day. The high correlation between the visual symptoms o f estrus and estradiol concentrations indicates that visual estrus detectio n is an efficient, reliable way to determine the right time for inseminatio n. (C) 2000 by Elsevier Science Inc.