Abstract:
454 Proc. Aust. Soc. Anim. Prod. Vol. 17 GROWTH AND REPRODUCTION IN LAMB OFFSPRING OF EWES TREATED WITH MELATONIN 2 2 REEVE 1, J. TILLBROOK , A., CONGDON , P., PEAKE1, B ., WILLIAMS2, A. & STAPLES2, L. Border Leicester x Merino (BLxM) ewes treated with melatonin implants (Regulin, Gene Link Aust Ltd) in Spring or early Summer bear more lambs than untreated ewes (Reeve et al. 1986). It is not known if the seasonal manipulation of the mothers will lead to disturbances of the growth or reproductive behaviour of the offspring lambs. In this study, the performance of lambs born to either melatonin (T) or control (C) BLxM ewes mated to Dorset rams (n=lOO/group) was observed. The trial was. replicated for both treated and untreated mothers lambing in May or July 1986 . May-born lambs were weaned on 19th Sep., and July-born lambs on 29th Oct. Live weights of ewe and ram lambs were monitored to determine growth rates. The ewe lambs of both ages were joined as one mob to fertile rams from 11th Feb to 10th Jun 1987, and matings and foetal numbers were recorded (Table 1). For ram lambs, the testis size was recorded regularly, and sexual activity (mounting) was observed at 12 months of age, in a pen test (Table 2). Birth weight, growth rate and fecundity of single-born lambs was greater than twin-born in all regardless of maternal trea-&3kt, Melatonin treatment of mOthers had no effect on birth weight or growth of single la&x. Ewe la& twins from treated ewes grew slightly slower to weaning (RO.05) and had a -inally lower birth weight. This trend continued to mr in the late lambing group. Melatonin tratment of significant effect on had reproductive performance of ewe offspring. Treatment of dams hadnoeffecton live weight, growth, or sexual activity of ram lb. Table 2 Live weight testicle size & sexual activity of male offspring of T&C ewes Ramlambs T'ment Live weight Testicular Number bomin ofdam n (kg) size (ml) sexually active MZiY Cont (0 5 50.0 237 2 Mel (T) 5 49.6 205 2 Cont (C) 5 49.5 142 5 Mel (T) 5 50.7 170 5 WeconcludethatRegu.lintratnxx&of BLxMewesin Springdoesnotresult in abnormal reproductive perfom of ram or ewe offspring at their 1st season. (P<O.O5) Reeve, J., Williams, A., McPhee, S., Peake, R. & Staples, L. (1986) Proc. Aust. Soc. Reprod. Biol. 18:25 w Agri & Rural Affairs, Vic.-Mrglenx & Werribee2 Res. Insts.