Lambing percentage will not be increased, in fact, ewes that breed later in the fall breeding season have more twins than ewes bred early in the season. The average number of ewes that a ram can serve varies with age, season, temperature, sex drive and physical condition of the ram. The ram can greatly influence the number of lambs born per ewe exposed as well as the number of ewes conceiving during the breeding season. Variation in sexual behavior can affect lambing rate. Some rams are more aggressive breeders than others.
Some rams mate repeatedly with the same ewe even though many ewes are in heat at the same time.
Malnutrition, internal parasites, or diseases may cause sterility or depress his desire to mate. Breeding soundness evaluation of potential sires is a recommended practice particularly in one-sire flocks where the entire lamb crop is dependent on one ram. It requires some technical training and special equipment and is usually done by a practicing veterinarian. It includes an evaluation of body soundness, reproductive tract soundness and semen quality. During the breeding season a marking harness with a crayon should be used on the ram or his breast can be smeared with a marking pigment.