Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 17 ATTEMPTS TO IMPROVE THE REPRODUCTIVE PERFORMANCE OF BORDER LEICESTER x MERINO EWE LAMBS JOINED IN THEIR FIRST SEASON. 393 C. EARL1, R. MALE1, S. MCPHEE 2, B. AYTON2, A. WILLIAMS2, & L. STAPLES2. The efficiency of prime lamb production could be increased by effective mating of maiden ewes and ewe lambs but the reproductive performance of maidens is characterised by a later occurrence of first oestrus, a shorter breeding season, and a lower ovulation rate than that of mature ewes Wheeler & Land 1977). While melatonin implants have been shown to improve the reproductive perfo mance of well grown maiden Merino ewes joined in Spring (Staples et al 1986) nothing is known of the effect of such treatment on immature Border Leicester x Merino (BLxM) ewe lambs. This study examined whether melatonin treatment of ewe lambs in Spring would improve their reproductive performance when they were mated in their first breeding season. Althoughmoreof the untreated group showed oestrus by the endof joining, there were no significant differences between groups in fertility or fecundity. A peak of oestrus occurred during the latter part of the mating period for both groups, but none of the animals mating at this time conceived. Previous studieshave shownthatBLxMewelar&sof the same pre-matingweight of theewe la&x in this study, but which gained weight (1Okg) over the mating period, produced 80% lambs (Earl unpublished data) so the low fertility in the trials may have resulted partly from the poor pasture conditions during the joining period. Melatonin treatmnts causmi no improvement in the reproductive performnce of imnature ewe lambs grazing poor pasture during mating and my have slightly delayed puberty in these l&s. STAPLES, L.D., McPEEE, S., AYt0N, B., REEVE, J. and WILLIAMS, A. (1986). Proc. Aust. Soc. Reprod. Biol. 18:26 -, A.F. and LWD, R.B. (197z. Anim. Prod. &363-376 x SA Dept Agr Strum Res Ctr, Box 618, Naracoorte, S.A. 5271. 2 Vic Dept Agri & Rural Affairs, Anim Res Inst Werribee, 3030.
