REPRODUCTIVE-PERFORMANCE OF ZEBU CATTLE IN MEXICO - INFLUENCE OF SEASON AND SOCIAL-INTERACTION ON THE TIMING OF EXPRESSED ESTRUS

The influence of herd interaction on the behavioural expression of oes trus of 32 and 38 nonpregnant Zebu cows was studied. Continuous observ ations were performed for a period of 44 days during the wet season an d 50 days during the dry period. Sexual activities were grouped into p ro-oestrus (the cow was active in mounting but not receptive), oestrus (the female was receptive), and metoestrus (cow was still active but not receptive). Significant differences (P < 0.01) were observed in th e duration of the pro-oestrous period, 14.9 h vs. 5.1 h in the wet and dry seasons, respectively. However, no differences (P > 0.10) in the duration of oestrus and metoestrus for the wet and dry seasons were ob served (10.4 h vs. 9.8 h and 4.2 h vs. 4.0 h, respectively). Only 10.8 % of the periods of sexual activity was observed when three or more co ws were concurrently displaying sexual activity. This suggests that Ze bu cows under field conditions tend to manifest synergistic sexual beh aviour.