Submitted to: Sheep and Goat Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2006
Publication Date: April 11, 2006
Citation: Burke, J.M. 2006. Lamb production of Dorper, Katahdin, and St. Croix bred in summer, winter, or spring in the southeastern U.S. Sheep and Goat Research Journal. 20:51-59. Interpretive Summary: The use of hair breeds for lamb production has increased significantly over the past few years because of ease of management. Little has been reported about out-of-season breeding and ewe lamb performance in the US, which leaves a knowledge deficit in lambing management of hair breeds. Dorper, Katahdin, and St. Croix ewes were all capable of breeding out-of-season; however summer heat stress increased pregnancy and lamb losses in Dorper ewes. These results indicate which breeds are suitable for seasonal breeding schemes in the southeastern US, which is important to seedstock and commercial sheep producers, scientists, and extension agents.
Technical Abstract: The objective was to examine ewe production traits and ability to breed out of season among Dorper (DO), Katahdin (KA), and St. Croix (SC) hair breeds between 2000 and 2005. Sheep were raised on tall fescue or bermudagrass overseeded with rye, and were supplemented with corn/soybean meal (16% CP with added lasolocid; up to 500 g/d for growing lambs and up to 1 kg/d for lactating ewes) and free choice trace mineral mix. Ewes were bred in late summer (August/September), winter (December), or spring (April/May) during a 30-d breeding period to respective ram breed. Lambs were weighed at birth and 60 days of age. Early pregnancy rates were greater for all breeds lambing in summer and lowest in fall, and lambing rates were lowest in fall for all ewes exposed. Pregnancy and lambing rate for DO ewes was greatest for ewes bred in winter compared with spring and late summer. Pregnancy and newborn lamb losses and birth weights were reduced for DO ewes bred in the spring compared with other seasons. Average birth weights of KA and SC lambs were not affected by season. Average litter weight of DO and KA lambs at 60 d of age was greater when ewes lambed in winter compared with other seasons, but weights of SC lambs were not influenced by season. In summary, DO, KA, and SC ewes are capable of out-of-season breeding in Arkansas. However, DO ewes in this flock appeared to be influenced by summer heat stress when lambing in fall, resulting in increased embryo and lamb mortality.