A note on the effects of calf stimuli on the response of Zebu cows to Synchro-mate-B

The effect of Synchro-mate-B (SMB) was measured on the estrous response and the establishment of cyclicity using different calf stimuli. Multiparous Z ebu cows, were divided in three groups. In the first, 32 animals were treat ed with SMB leaving the calves present (SMB + CP). In the second, 33 cows w ere treated with SMB and calves partially removed (fence-line contact) for 48 h (SMB + CPR). In the third group (n = 33), cows received SMB and calves were removed for 48 h (SMB + CCR) with no visual or olfactory contact. A c ontrol group (CG, n = 33) involved neither SMB or calf separation. Blood sa mples for progesterone assessment were obtained at 11 and 4d prior to SMB t reatment and on days 7 and 11 after the average return to estrous for each group. All animals were observed continuously for mounting activity during 72 h after SMB implant removal. A significant difference (P < 0.05) in estr ous response was found between SMB-treated and non-treated animals, regardl ess of calf management (56 versus 8%, respectively). Cows with SMB + CCR an d SMB + CPR came into estrous sooner (P < 0.05) (26.5 +/- 2.6 and 18.1 +/- 4.94 h, respectively), than those that remained with their calf present (40 .4 +/- 12.8 h). Cows with SMB + CCR displayed longer (P < 0.05) periods of mounting behavior (13.0 +/- 4.4 h) in comparison with SMB + CPR and SMB + C P (7.4 +/- 1.8 and 8.1 +/- 4.0 h), respectively. Furthermore, 84% (P < 0.05 ) of the cows in the SMB + CCR had high concentrations of progesterone afte r mounting behavior was displayed, in comparison with 68 and 54% in the oth er two groups, respectively. No difference was found (P > 0.05) in the numb er of mounts per hour in estrous. It was concluded that: (1) SMB increases the number of cows that display estrous; (2) temporary weaning shortens the period from SMB implant withdrawal to mounting activity, and (3) SMB + CCR , increases the length of sexual receptivity and the number of cows that co ntinue to cycle. (C) 2001 Elsevier Science B.V. All rights reserved.