Influence of bull biostimulation, season and parity on resumption of ovarian activity of zebu (Bos indicus) cattle following parturition

A total of 135 postpartum suckled zebu cows were assigned randomly at calvi ng to two treatments: cows exposed to vasectomised bulls (Mature Bull Expos ure, MBE) and cows not exposed to bulls (No Bull Exposure, NBE) for a perio d of 150 days postpartum. This study was conducted to determine the influen ce of bull biostimulation, season and parity on postpartum reproductive per formance of Bos indicus cattle. The trials were conducted in two seasons: c ows calving in the dry season and cows calving in the rainy season. Cows wi th an increase in serum progesterone (P-4) concentration of >1 ng/ml from t he weekly blood samples were used to analyse the number of days from calvin g to the time of resumption of ovarian activity. The introduction of vasect omised bulls shortened the postpartum anoestrus in cattle following calving . Mean interval from calving to resumption of ovarian activity for the MBE co ws was 71.7 days, which was significantly earlier following calving than th e NBE cows with a duration of 77.8 days. By 60 to 80 days postpartum, the p roportion of cows at resumption of postpartum activity for MBE cows was gre ater than for the NBE cows. Mean interval from calving to resumption of ova rian activity for cows that calved in the dry season was 71.3 days, which w as significantly earlier than for cows that calved in the rainy season (78. 6 days). At 60 days postpartum, the proportion of cows at resumption of pos tpartum ovarin activity fur cows that calved in the dry season was greater than the cows that calved in the rainy season. Mean interval from parturiti on to resumption of ovarian activity for cows with three to five calvings w as 65.1 days, which was significantly earlier than the value of 71.2 days f or cows with one to two calvings. By 60 to 80 days postpartum, the proporti on of cows at onset of ovarian activity for cows with three to five calving s was greater than those cows with one to two calvings. Cows that calved in the dry season completed uterine involution by 24.4 days, which was signif icantly shorter than the duration of 26.5 days for cows that calved in the rainy season. Cows with three to five calvings completed uterine involution earlier than those with one to two calvings. It is concluded that bull-cow biostimulation influences reproductive activity in the cow possibly throug h olfactory cues (pheromones). (C) 2000 Elsevier Science B.V. All rights re served.