The effects of increased prolificacy on lamb and ewe mortality in an intensive hill sheep system

Abstract

Increased prolificacy is often believed to increase the incidence of both lamb and ewe mortality especially in harsher environments. Fecundin® (Coopers Pittman Moore) is a vaccine which leads to immunization against androstenedione and a resulting increase in prolificacy (Rhind, 1987). The use of this drug gives a method of manipulating prolificacy without confounding any effects with improved nutrition, the most usual means of modifying reproductive success.A programme was commenced in 1985 in which half the ewes in a flock of Scottish Blackface ewes was vaccinated with Fecundin (F), the remainder left unvaccinated (N). In subsequent years ewes were maintained on the same treatment. The data presented here are an analysis of a single age group of ewes completing a full lifetime on each treatment. Eighty-five ewes were allocated at random to each treatment. These were vaccinated in autumn 1985, given a booster vaccination 4 weeks pre-ram joining in 1986, 1987 and 1988 and sold as ‘cast for age’ after lamb weaning in 1989. With the exception of injection with Fecundin, at all times management was independent of treatment.