Postpartum Reproductive Performance and Serum Progesterone Concentration in Early-Weaned Beef Cows

Abstract

These experiments were carried out to clarify the effects of suckling on postpartum reproduction and serum progesterone concentration in beef cows. Each of twenty-seven Japanese Black females was assigned to one of three treatment groups: (1) ten calves were removed from the dams at birth (DO), (2) seven calves were removed at 30 days of age (D30) and (3) ten calves were removed at 60 days of age (D60). Nonsuckling significantly shortened the interval from calving to the first postpartum ovulation (DO vs. D30 and D60, P<0.01). Although the first postpartum ovulation was accompanied by estrous behaviour in six out of ten cows in the D0 group, all were quiet ovulations in the D30 and D60 groups. Furthermore, the suckling of calves increased the proportion of cows not exhibiting estrus at the second postpartum ovulation, and a significant difference was observed in the interval from calving to the first postpartum estrus among these three groups(16.3±7.0 days, 40.3±5.1 days and 56.8±10.0 days, P<0.01).Serum progesterone concentrations after the first ovulation tended to be higher in the D0 group. However, in all groups, the interval from the first to second ovulation was shorter than the second cycle and serum progesterone levels at the peak after the first ovulation were lower than those after the second ovulation, indicating that most corpora lutea formed after the first ovulation were not fully functional. Starting breeding 40 days postpartum resulted in an equal interval from calving, to conception and a similar number of inseminations required for conception in all three groups.