A Note on Estrous Response in Cows Induced With or Without the Application of Estrogens, and Their Effect in Nontreated Herdmates

To determine if providing estrogen with a control internal drug (progesterone) releasing device (CIDR) increases the number of cows showing estrus but not ovulating, and if there is synchronization of estrus in nontreated cows, 54 Brahman cows with no calf present were synchronized sequentially with CIDR on days 1, 7, 13, and 22. The numbers of cows treated on each of the 4 days were 4, 6, 10, and 7, respectively. These animals did not receive an estrogen injection (CON) on day 3, 10, 16, and 22. A set of matching animals was synchronized with CIDR but given an injection of 1.0 mg of estradiol benzoate 24 hours after implant withdrawal (EB). Ultrasound examinations and blood samples were taken on the day of CIDR implant, on the day of withdrawal, and 10 days following the average response time to estrus in the experimental group. Of the EB and CON cows, 81% (22/27) and 48% (13/27), respectively, displayed estrous behavior after implant withdrawal. The number of animals displaying estrus and ovulating was similar (10 and 12, respectively) for EB and CON cows. However, more cows (P=0.02) showed estrus but did not ovulate in the EB group (n=12) than in the CON group (n=1). Onset of estrus was different (P=0.05), averaging 43 ± 7 hours and 48 ± 8 hours for the EB and CON group, respectively. No differences were found in estrus intensity and length. There was a tendency for cows to form sexually active groups irrespective of the day of treatment, and this grouping behavior was even more evident as the experiment unfolded and the number of treated cows increased. There was a significant difference (P<0.05) in favor of CON cows in the display of estrus simultaneously with other cows in comparison with EB cows. It was concluded that cattle synchronized in alternation are capable of displaying behavioral estrus, but some do not ovulate following this event.