Reproduction is an important factor in raising healthy sheep. The gestation period of sheep influences many sheep management decisions.
Ewes usually give birth to one or two lambs each a year. Ewe lambs are bred at five to nine months of age and a minimum of 70 to 100 pounds to successfully carry and raise lambs. Some sheep producers wait until a ewe is two years old to raise lambs to give the ewe adequate time to mature. Breeds such as the Finnsheep are known for producing more than two lambs per year.
Ewes are seasonally polyestrus. They are most fertile when the days are growing shorter, usually during the months of September, October and November. Cool weather also is correlated with ewe estrus cycles. Average ewes have an estrus cycle of 17 days. Ewes are in estrus or heat about 24 to 36 hours.
Flushing has been shown to increase the number of lambs born per ewe. Flushing involves feeding extra or more nutritious feed around the time of breeding. The ovary releases more eggs and therefore more lambs are carried to term.
If a ewe is bred, the gestation length is 148 days or about five months. The length of gestation varies slightly due to several factors. Ewes carrying male lambs usually have a slightly longer gestation than ewes carrying female lambs. Older ewes carry lambs slightly longer than younger ewes and ewes pregnant in the spring have a longer gestation than ewes pregnant in the fall. Ewes with single lambs may have a longer gestation than ewes carrying twin or triplet lambs.
Many ewes are bred in the fall and lamb in the spring. During the spring green grass for grazing may be more available than during other times of the year and the temperature is milder.
Accelerated lambing involves breeding ewes so they produce lambs more than one time per year. For example, ewes may be bred to raise three lamb crops in two years. Ewes of the Rambouillet, Dorset, Polypay and Finnsheep breeds are more successful in accelerated lambing programs than other breeds. Ewes are bred at least thirty days after lambing.
There are several methods to determine if a ewe is pregnant. Some producers attach chalk markers to the rams. When a ewe is bred, a chalk mark is placed on the ewe's back. Ultra sound may be used to determine pregnancy. The most common method of pregnancy detection is careful examination of the udder. The udder is checked for bagging (swelling) which occurs prior to lambing.
At approximately 148 days after breeding, the lambs will be born. The normal presentation of the lambs is nose and front feet first with the head up. Abnormal presentations include one or both legs back or the entire lamb backwards.
With proper management, ewes will successfully raise healthy lambs each year.