Estrous cycles are usually affected by the seasons. Ewes will begin to exhibit estrus when length of day begins decreasing and will come into heat every 16 to 17 days until they are bred or return to anestrus. Thus, the most natural time for sheep to breed in the U.S. and Canada is the fall (October-November).
Reproductive Characteristics of Ewes
Prior to breeding, ewes should be dewormed and have their hooves trimmed. If there is a history or risk of abortions in the flock, ewes should be vaccinated prior to breeding. Only healthy, reproductively sound ewes should be exposed to rams for breeding.
Most producers flush the flock two to four weeks before turning the ram in. This is done by gradually increasing feed intake so that breeding animals are getting maximum nutrition during the early breeding season. Then feed is reduced again to just above maintenance for gestation. Research indicates that good nutrition increases ovulation, conception rate and reduces early embryonic mortality.
The average gestation length in sheep varies from 142 to 152 days. Ewes carrying multiple lambs tend to have shorter gestations.
Shearing, vaccinating, working ewes, and pronounced changes in feeding practices should be avoided during the first 30 days of gestation. Ultrasonic pregnancy scanning can be done on ewes from 35 to 60 days after breeding. Nutrition during early gestation is quite simple. Ewes need only slightly above maintenance levels of nutrition for the first 15 weeks of pregnancy.
Late gestation (last four to six weeks) is a critical period for ewe reproduction. This is when the majority of fetal growth is occurring, placing increasing nutritional demands on the ewe. Ewes consuming inadequate diets are prone to pregnancy toxemia and milk fever. Nutrition in late-pregnancy affects the size and vigor of lambs and the milk producing ability of the ewe.
The ram is an important member of the flock, yet often the most neglected. Purchase rams at least several months before the breeding season. Rams need time to get acclimated to their new surroundings and be started on the diet that they will be consuming during the breeding season. They should be dewormed, have their hooves trimmed, and should be shorn if the weather is warm. A breeding soundness examination with a semen evaluation should be performed by a veterinarian prior to turning the ram in with the ewe flock. Proper management of rams will go a long way towards ensuring a successful lambing season and profitable sheep operation.