Reproductive performance of ewes exposed to vasectomized rams before breeding and forced exercise before lambing

Twenty days before a regular fall breeding season, 93 mature Rambouillet ewes were randomly allotted to one of two groups to examine the response of cycling females exposed to sterile rams. Six vasectomized rams were joined with 46 ewes during the 20-day period while 47 ewes remained separate from the rams. All ewes were judged to have been cycling either by paint marks from rams on treated animals or by the cyclic nature of progesterone (sampled at four-day intervals) profiles in control ewes. After removal of sterile males, fertile Debouillet rams remained with the ewes during a 34-day breeding season. Approximately six weeks before beginning the lambing season, one-half the females in each sterile ram treatment group were forced to walk 0.8 km per day to examine the influence of exercise on subsequent reproductive performance. Presence of sterile males did not alter (P>0.10) lambing rate, average lambing date or percentage of ewes lambing during thirds of the lambing season suggesting that prebreeding exposure of cycling ewes to vasectomized rams does not enhance lambing rate or shorten the lambing season. Forced exercise resulted in increased daily feed consumption which was reflected in heavier (P<0.05) lamb birth weights. Percentage of ewes experiencing either dystocia or pregnancy toxemia was similar (P>0.20) in exercised and unexercised animals. Moderate exercise during late gestation may increase lamb birth weight without increasing lambing difficulty.