Resumption of postpartum ovarian cyclicity after different suckling manipulation treatments in primiparous beef cows

The aims of this experiment were to study suckling manipulation strategies, such as early weaning, suckling inhibition with nose plates or temporary weaning for 5 days, on resumption of ovarian cyclicity in anoestrous beef cows. Seventy-four primiparous Aberdeen Angus and Hereford cows with a mean body condition score of 3.8 +/- 0.1 (mean +/- s.e.m, 1-8 scale) grazing together on rangeland were used. At 71 days postpartum (Day 0) animals were assigned to one of four groups as follows: (1) suckling group (S, n = 14): cows were suckled throughout all the experiment; (2) nose plates group (NP, n = 20): nose plates were placed to calves for 14 days; (3) temporary weaning group (TW5d, n = 20): calves were isolated from their dams for 5 days; (4) early weaning group (EW, n = 20): calves were definitely weaned. After treatments, weekly serum progesterone concentrations were measured for 9 weeks. EW and NP cows had shorter intervals between treatments and resumption of ovarian cyclicity (19.6 +/- 1.7 and 24.5 +/- 3.3 days versus 40.6 +/- 3.5 and 37.5 +/- 4.0 days for EW, NP, TW5d and S, respectively, P < 0.01). A higher proportion of the EW group showed luteal progesterone concentrations the first week after treatments (20 versus 5, 0 and 0% for EW, NP, TW5d and S, respectively, P < 0.05), then proportions of EW and NP cows resuming postpartum cyclicity were similar throughout the remainder of the study. Temporary weaning for 5 days showed no effects on ovarian cyclicity resumption. When body condition score is not very limiting, restricting suckling over 14 days with nose plates is a useful strategy to induce postpartum cyclicity in range cow herds with effects similar to early weaning.