THE EFFECT OF IMPLANTATION OF LOWLAND EWES WITH MELATONIN ON THE TIME OF MATING AND REPRODUCTIVE-PERFORMANCE

Two trials, involving a total of 1006 Mule ewes and 1862 Suffolk-X ewes, were conducted to investigate the ability of implantation with melatonin to induce early breeding in lowland sheep flocks. Dates of implantation ranged from mid May to late June for Suffolk-X flocks and mid May to early July for Mule flocks. From the mating patterns obtained it is suggested that the optimum implantation date is mid May to mid June for Suffolk-X ewes and mid June to mid July for Mule-type ewes. Melatonin treatment also significantly increased the mean litter size per ewe exposed to the ram (resulting from a 6-week mating period) when the data were pooled across flocks, but the magnitude of this effect varied across flocks. Part of this overall mean increase in Mule ewes (+0.84 and +0.50 extra lambs per ewe in trials 1 and 2 respectively) was due to an increase in the proportion of ewes mating and lambing and part of it (+0.13 and +0.17 extra lambs per ewe, respectively) was due to an increase in litter size per ewe pregnant. In the Suffolk-X ewes there was evidence that the overall mean benefit following implantation with two implants (+0.31 extra lambs per ewe) was greater than that following implantation with one implant (+0.14 extra lambs per ewe), with all of the increase at the lower dose level and +0.21 extra lambs per ewe at the higher dose being due to an increase in litter size per ewe pregnant.