INCREASED LAMB PRODUCTION WITH RAMS EXPOSED TO SHORT DAYLENGTHS DURING THE NONBREEDING SEASON

Exposure of rams during the nonbreeding season (anestrous period) to short daylengths will initiate a new sexual cycle characterized by testicular growth, increased mating activity and improved semen quality. Lambing results accumulated from 300 potential matings indicate that rams exposed to artificial photoperiods of 8 hr light and 16 hr darkness for 10 weeks (referred to as rams on short-days) are more fertile than control rams maintained under the relatively long days of spring. When five control rams were penned individually with 30 ewes synchronized with progestogen and PMSG, 67% of the ewes were mated. Eighty-nine percent of the ewes were mated with rams on short-days. Expressed as a percentage of the total ewes exposed per ram, 32% lambed from control matings; whereas, 67% lambed following exposure to rams on short-days. Combined with a higher number of lambs born per ewe lambing, rams on short-days sired 2.5 times more lambs than did control rams. Results of this study show that the ram contributes significantly to the fertility of single-sire matings and that lamb production can be increased substantially by experimental manipulation of photoperiod. Exposure of both rams and ewes to artificial photoperiods may be a useful management tool to distribute the lamb crop to predetermined, specified times of the year