Female sheep, technically called ewes, are pregnant for 138 to 149 days. The average gestation period is 146 to 147 days. There are no visible signs of pregnancy until about six weeks before birth.
Pregnancy can be confirmed with an ultrasound around 35 to 60 days after breeding. A single ram is often used to impregnate an entire herd of sheep. The breeding season for most sheep is in autumn although certain types of sheep breed year round. Ewes reach puberty between 5 to 12 months of age, but they should not be bred until they reach 70 percent of their mature size.