Effects of parasite control in the peri-parturient period on lamb birth weight and liveweight gain

Abstract

The effect of pre- and post-lambing anthelmintic treatment of the ewe on subsequent lamb production was studied. Sixteen groups of 25 maiden Border Leicester x Merino ewes were given combinations of a pre- and post-lambing 'drench' with thiabendazole. All groups were pastured on separate paddocks giving four replicates of each treatment program. Lamb liveweight changes were recorded for 19 weeks. A pre-lambing drench was found to increase lamb birth weights, and this advantage persisted until the lambs were drafted for slaughter in the nineteenth week from the beginning of lambing. The advantage was greater for twin compared with single lambs. The post-lambing drench had no effect on liveweight gain up to week 13, but had a significant effect over the next six weeks. This result seemed to have been related to the lower parasite burdens being passed from the ewe to the lamb, as a result of the post-lambing drench. This drench controlled the rapid rise in faecal egg counts which was observed in the lambs of untreated ewes after the eleventh week. At the time of lambing, pasture contamination was probably lower than under many practical field situations and results of the same magnitude may not occur regularly. The implications, however, are greatest in flocks with a high twinning performance where early drafting of a high percentage of twin lambs is important for economic or pasture management considerations.