The effect of tilmicosin administered to ewes prior to lambing on incidence of clinical mastitis and subsequent lamb performance

The effect of tilmicosin on the incidence of clinical mastitis and subseque nt lamb performance was studied in 9 sheep flocks in Ontario. Ewes were tre ated randomly with either tilmicosin or placebo approximately one month pri or to lambing. Outcome was assessed by comparing rates of clinical mastitis , palpable udder abnormalities, and preweaning (50-day) lamb weights betwee n the 2 treatment groups, while controlling for other important variables. Lambs raised by multiparous en es treated with tilmicosin were significantl y heavier than lambs from placebo-treated multiparous ewes at 50 days. Lamb s from tilmicosin-treated ewes were on average 0.52 kg heavier than lambs i n the placebo group. There was no difference between treatment groups in th e weight of lambs from first parity ewes. Tilmicosin treatment resulted in a 43% decrease in palpable udder abnormalities. incidence of clinical masti tis did not differ between experimental groups. The administration of tilmi cosin prelambing, at the time of routine clostridial disease vaccination, m ay be a beneficial and convenient way to reduce mastitis infection and impr ove the preweaning gain of lambs.