Influence of suckling frequency and bromocryptine treatment on the resumption of ovarian cycles in post-partum beef cattle.

Effects of restricted suckling frequency and bromocryptine treatment on return of ovarian cycles after calving were studied on 151 Angus and Friesian Angus crossbred cows. A control group consisted of cows and calves grazed together. In two groups, calves were allowed to suckle for one hour only each morning (1 x S) or one hour each morning and afternoon (2 x S). A further group of cows, grazed with their calves, were treated with 10 mg bromocryptine per day from days 2-11 post-partum (BCT). Interval from calving to resumption of ovarian cycles, assessed from oestrous records and weekly progesterone samples, did not differ between control and 2 x S cows. Interval from calving to a recorded progesterone sample greater than 1.7 ng/ml associated with oestrus in 1 x S cows was 13 days shorter than for control cows (63 vs 76 days, SED = 1.4, p < 0.05) although, the difference in interval to first oestrus of 11 days was not significantly different in these groups (64 vs. 75 days, SED = 4.5). Time from calving to resumption of ovarian cycles did not differ between BCT and control cows. Collectively these data indicate that suckling frequency per se is not a major factor influencing resumption of ovarian cycles after calving. Instead they suggest the association of the cow and its calf may influence the long post-partum anoestrous intervals in these animals.