Sexual behavior of Zebu cattle (Bos indicus) following estrous induction by Syncro-Mate B, with or without estrogen injection

The effect of estrogen administered with norgestomet implants in the expres sion of behavioral estrous of Zebu cattle was studied in a herd of Is cycli ng Brahman cows, in two trials. In the first and second trials, six differe nt cows were treated with progestagen on successive days. In addition, in t he first trial, estrogen injection was applied with the treatment. With the purpose of enhancing mounting behavior in treated and/or non-treated anima ls, on the third day of each trial, three other cows with an active CL were injected with 25 mg of PGF(2)alpha. All animals were examined three times a week by rectal ultrasound, and a blood sample was also taken for progeste rone analysis. Sexual activity was monitored by a closed-circuit TV from 15 00 to 0600 h. Direct observation was carried out from 0900 to 1200 h. A tot al of 15 cows displayed 36 mounting periods (11 with ovulation). Twenty-fiv e annovulatory estrous periods were observed, 77% supported by large follic les. More cows (66% vs. 16%) showed mounting activity when estradiol valera te was used as part of the progestagen treatment (P=.03). Ovulation rate in response to the effect of norgestomet implant was 16%, independent of trea tment. It is concluded that estrogen administered with norgestomet implants increases the expression of behavioral estrous in Bos indicus cattle but d oes not improve ovulation rate. (C) 2000 Elsevier Science Inc. All rights r eserved.