Resumption of postpartum ovarian cyclicity after different suckling manipulation treatments in primiparous beef cows T. de Castro A,B,E , D. Ibarra B,C , M. Rodriguez B , L. Valdez B , N. Benquet B and E. Rubianes D A Instituto de Reproducción Animal Uruguay, Fundación IRAUy, Camino Cruz del Sur 2250, Montevideo, Uruguay. B Department of Animal Reproduction, Faculty of Veterinary Sciences, Lasplaces 1550, 11600 Montevideo, Uruguay. C Department of Bovines, Faculty of Veterinary Sciences, Lasplaces 1550, 11600 Montevideo, Uruguay. D Department of Animal Sciences, Faculty of Agricultural Sciences, Garzón 780, Montevideo, Uruguay. E Corresponding author. Email: tdec@adinet.com.uy Abstract. 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. Additional keywords: early weaning, nose plates, temporary weaning. Introduction Suckling and undernutrition determine the length of postpartum anoestrous interval and therefore are impediments to biological and economic efficiency in range cow herds (Randel 1990; Hawkins et al. 2000; Yavas and Walton 2000). Uruguay has more than 12 million beef cattle raised predominantly on extensive rangeland conditions and national weaning rates are less than desirable (mean 62%), mainly due to extended postpartum anoestrous intervals (Quintans et al. 2009). Strategic management of suckling at the beginning of the breeding season to shorten postpartum anoestrous interval and to ensure that conception can occur appears to be essential in systems that have a great dependence on range vegetation (McSweeney et al. 1993; de Castro et al. 2006). Early weaning at 30–60 days postpartum induces cyclicity and increases pregnancy rates in anoestrous beef cows (Williams 1990; Hoffman et al. 1996; de Castro et al. 2006). However, it has been associated with increased labour and difficult management of the early weaned calf, consequently it is recommended in situations when cows are in such poor body condition at breeding that adequate rebreeding performance is compromised (Yavas and Walton 2000). Beef production systems in Uruguay normally wean their calves at 5 or 6 months of age, so weaning at 70 days postpartum is considered early weaning (de Castro et al. 2006). Intermediate alternatives such as temporary weaning or restriction of weaning with nose plates could be useful in situations when body condition score (BCS) is not very limiting (Stahringer 2001). Effects of temporary weaning for 48–96 h on resumption of ovarian cyclicity and subsequent pregnancy rates are highly variable depending mainly on BCS, days postpartum and parity (Makarechian and Arthur 1990; Williams 1990). Application of nose plates to calves to temporarily prevent suckling is commonly used by cow-calf producers and can be a low-cost alternative to shorten postpartum anoestrous interval (Holness and Hopley 1978; Mukasa-Mugerwa et al. 1991; Stahringer 2001). However, solid results under field conditions are scarce (Mukasa-Mugerwa et al. 1991; Quintans et al. 2009). The aims of this experiment were to study the effectiveness of different suckling manipulation strategies such as early weaning, suckling inhibition with nose plates or temporary weaning for 5 days, on resumption of ovarian cyclicity of primiparous beef cows. CSIRO PUBLISHING www.publish.csiro.au/journals/an Animal Production Science, 2011, 51, 111–114 Ó CSIRO 2011 10.1071/AN10108 1836-0939/11/020111