Purdue University Cooperative Extension Service West Lafayette, Indiana
SYSTEMS OF MANAGEMENT FOR EWES AND IAMBS
J. B. Outhouse, Animal Sciences Department
AS-400 Rev. Oct. 1972 Animal Sciences
WINTER LAMBING
Most of the lambs produced in Indiana are born in the winter -- January through March. This is because late August to November is the period of greatest fertility in the ewe, and therefore, the traditional breeding season for most Indiana sheep flocks.
For many farmers, winter is the best time for lambing, since it does not interfere with crop production; pasture is available for finishing lambs; and early-born lambs can be marketed during the season of highest prices -- prior to July 1, when hot temperature reduces their gains.
Winter lambing does have some disadvantages, however. Lamb losses in January and February are usually greater because of the weather; shelter must be provided for both ewes and lambs; harvested forages must be provided during the period of greatest nutritional need; and the cost of feeding and storing of these forages together with removing manure produced, increases the direct costs of production. These increased costs must be recovered by higher lamb prices or the returns to labor and management will be reduced.
OUT-OF-SEASON LAMBING
In an attempt to reduce some of the costs of housing, forage harvesting and manure handling and permit sheep to utilize pasture during periods of greatest nutritional needs, some sheep producers are considering other lambing periods. These include fall lambing (September-October) or spring lambing (March-April) on once-a-year ba-
sis and accelerated lambing every eight months (January-February, September-October, May-June). Under the accelerated system, two flocks can be alternated, producing lamb crops every 4 months. This gives more efficient use of rams, facilities and labor, a better flow of lambs to market and a more even distribution of income from the sheep enterprise throughout the year.
Any out-of-season lambing system requires breeds of sheep with a short anestrus that will mate other than during the fall months. Such breeds include the Rambouillet, Merino, Dorset and Tunis and usually their first-cross progeny. The Columbia, Corriedale, Targhee, Panama and Debouil-let, which are related to the Rambouillet and Merino, tend to have the same breeding habits but to a lesser degree.
Many other breeds have individuals which have produced out-of-season lambs under natural conditions and may respond to selection for this trait; however, the progress will be slow. Ewes that do not respond should be give a second opportunity to mate during the normal breeding season to maintain a full production cycle.
Extending the breeding season by hormone treatment may have a practical use in promoting out-of-season breeding. The recommended procedure is 12-15 days exposure to progestogen followed by an injection of 500-700 IU of gonadotrophin at the end of progestogen treatment and then a second injection of gonadotrophin 16 days later with matings at both periods. This produces synchronization of estrus among ewes in the flock and normally results in shorter breeding and lambing periods.