Utilizing the Ram Effect for Spring Breeding
Livestock Update, April 2009
Scott P. Greiner, Ph.D., Extension Animal Scientist, VA Tech
Fall-born lambs marketed November through February have commanded high prices in recent years. These high prices have been the result of strong demand for lambs during these months coupled with relatively low supplies (particularly for lambs weighing 50 to 100 pounds). Consequently, production systems that utilize spring breeding (fall lambing) warrant consideration. However, the reproductive seasonality inherent to the biology of sheep makes this practice challenging, since many breeds are anestrous from April through July. Fertility in both the ewe and ram are affected by season of the year. Successful spring breeding starts with the utilization of genetics that have out-of-season capability. Breeds noted for this ability include Dorset, Polypay, Rambouillet, Finnsheep, hair breeds (Katahdin, St. Croix, Blackbelly), and crosses of these breeds. Considerable variation exists within these breed for fall lambing potential, and selection for this trait needs to be a priority for operations that utilize an extended breeding season.
Genetics, coupled with proper nutrition and management are key components for spring breeding success. One such management practice- the “ram effect” is commonly utilized to induce ovulation in anestrous ewes that have been previously isolated from rams. The ram effect is an effective, inexpensive, practical means to increase percentage of ewes lambing out of season. Utilization of the ram effect requires ewe isolation from rams for a minimum of one month, and preferably longer. Isolation from rams needs to be complete by avoiding fenceline contact and any association with rams (sight, smell, touch). Upon joining rams with ewes that have been previously isolated, ewes will ovulate with 7 days after introduction of the rams. However, less than 20% of the ewes will be in heat during these first 7 days (silent heat). Active estrus (heat) and ovulation will occur 17 to 24 days after introduction of rams, resulting in pregnancy. Breed of ewe is an important factor in response to the ram effect. Ewes will be more responsive to the ram effect as they reach the end of anestrous (are ready to start cycling), and therefore ewes with the genetic propensity to breed out-of-season respond most favorably to the ram effect in the spring. Vasectomized teaser rams are frequently used during the first two weeks since there is a delay in estrus with the ram effect. Fertile rams need to be placed with the ewes after 14 days. Aggressive rams (both fertile rams and teasers) with high libido are most effective in eliciting a response in the ewe. It is important that rams receive a breeding soundness exam prior to spring breeding to ensure fertility.
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