The reproductive performance of sheep carrying natural infections of gastro-intestinal nematodes

Abstract

Reproductive performance of a flock of 63 ewes carrying natural infections of gastrointestinal worm burdens was studied. Parameters monitored included: ovarian activity through progesterone profiles, parturition intervals, birth weights, mortality rates of offspring and worm burdens through faecal egg counts. Mean lamb birth weight was 2.6±0.48, litter size was 1.1 lambs and up to 50% of the ewes lambed two or more times within the 18 month period. Twining rate was 6%, with 4.5% abortions and a mortality rate of 37% up to three months of age. There were significantly less lambs born in the late wet season, than any other season, lambing percentages being 9.9, 23.3, 25.9 and 38% for the late wet, late dry, early wet and early dry seasons, respectively. Mean lambing intervals was 192±7.5 days in 17% of ewes and 220±10.4 days in another 34.8% of the animals. The remaining 47.8% had mean LI of between 250-349 days. EPG was significantly lower (p<0.05) in ewes with mean LI of 192 days (5025EPG) but was not significantly different in ewes with longer LI. EPG ranged from 13011 to 16317 in these groups. Progesterone profiles showed that long lambing intervals was due to delayed resumption of ovarian activity post partum. In addition to seasonal variation in availability of quantity and quality of feed, helminthosis may have an effect on reproductive efficiency in sheep, mediated mainly through effects on body condition which ultimately affects re-breeding intervals. © 2008 Academic Journals Inc.