Submitted to: The Shepherd
Publication Type: Popular publication
Publication Acceptance Date: 1/12/2009
Publication Date: 3/1/2009
Citation: Notter, D.R., Leeds, T.D., Mousel, M.R., Leymaster, K.A., Lewis, G.S. 2009.Does breed of ram affect ewe and lamb productivity?. The Shepherd. March Issue. pp. 8-10. Interpretive Summary: Systematic use of breed diversity in terminal crossbreeding systems can improve the efficiency of commercial lamb production. In such a system, rams of the terminal sire breeds are expected to increase lamb weaning weights, postweaning growth potential, and carcass leanness, muscling, and yield, without increasing the rate of lamb mortality or reducing the reproductive performance of the ewes. However, lamb mortality can increase with terminal sire crossing for many reasons, such as increased lambing difficulty associated with excessive size and weight of lambs at birth. Thus, in 2005 the USDA, ARS, U.S. Sheep Experiment Station, Dubois, Idaho, initiated a 3-year study to provide a comprehensive evaluation of lamb survival, growth, postweaning feed efficiency, carcass merit, and meat characteristics of four terminal sire breeds for use in Western range production systems, and to develop recommendations and strategies for optimal use of breed resources in terminal-sire mating systems. This report summarizes the effects of sire breed on ewe reproduction and on the survival and growth to weaning of the crossbred lambs produced during the first 2 years of the project. Data from this study indicate that breed of ram should be expected to affect lamb birth weights. However, breed of ram should not affect fertility or litter size of the ewes, and it should not affect lamb survival from birth to weaning. Based on data from this study, lambs with below-average birth weights are less likely to survive from birth to weaning than are heavier birth-weight lambs, regardless of breed. Lambs with birth weights that were 0.45, 0.91, or 1.36 kg (i.e., 1, 2, or 3 lb) less than the flock average of 5.2 kg (i.e., 11.5 lb) had 2.5-, 7-, and 25-fold greater risks of dying. By contrast, increasing lamb birth weights from the observed mean of 5.2 kg to the maximum observed value of approximately 8.2 kg (i.e., 18 lb) had essentially no effect on lamb survival. Additional data from this 3-year study will be used to quantify the effects of ram breed on postweaning growth potential, leanness, muscling, carcass yield, and carcass value of crossbred market lambs. When complete, data from this study should enhance the development of terminal crossbreeding systems and improve the efficiency of commercial lamb production.
Technical Abstract: Systematic use of breed diversity in terminal crossbreeding systems can improve the efficiency of commercial lamb production. Data from controlled research should be used to select the genetic line or lines of rams to use in terminal crossbreeding systems. Thus, research is underway at the USDA, ARS, U.S. Sheep Experiment Station, Dubois, ID, to determine whether breed of ram affects ewe and lamb productivity. This research is a collaborative effort of scientists at ARS-Dubois, ID, ARS-Leetown, WV, ARS-Clay Center, NE, and Virginia Polytechnic Institute and State University. Key results from the first 2 years of this 3-year study to compare the Suffolk, Columbia, Texel, and USMARC-Composite breeds are presented here to update the U.S. sheep industry on the progress of this research. Rams in the study were mated with adult (3- to 7-year-old) Rambouillet range ewes. There were 636 exposures and 608 lambings, and a total of 1,243 crossbred lambs were produced. 1) Breed of ram had no significant effect on fertility or litter size of the ewes. When mated for 21 days in small pens beginning in mid-October, fertility of the adult Rambouillet ewes averaged 95.6%, average litter size was 2.04, and average number of lambs weaned per ewe lambing was 1.50. 2) Lambs sired by Suffolk rams had an average birth weight of 5.3 kg (i.e., approximately 11.6 lb) and were significantly heavier than lambs sired by Texel or USMARC-Composite rams (both 5 kg [11.0 lb]). Lambs sired by Columbia rams had an average birth weight of 5.1 kg (11.3 lb) and did not differ significantly from lambs sired by any of the other breeds. 3) There were no significant differences in lamb survival among sire breeds. Total lamb death losses ranged from 10.6% for Suffolk-sired lambs to 16.6% for Texel-sired lambs. These figures include stillborn lambs and all death losses from birth to weaning. Inferences from these data about effects of sire breed on crossbred lamb survival are valid for adult, nonprolific ewes, but may not be valid for more prolific ewe types or younger ewes. 4) Lambs were herded with their dams on sagebrush steppe and subalpine range and weaned at an average age of 130 days. Suffolk-sired lambs had an average weaning weight of 39.5 kg (87 lb) and were significantly heavier at weaning than lambs sired by Columbia (37.6 kg [83 lb]), USMARC-Composite (37.2 kg [82 lb]), and Texel (36.7 kg [81 lb]) rams. Columbia-sired lambs were significantly heavier at weaning than Texel-sired lambs. Weaning weights of USMARC-Composite-sired lambs were intermediate to those of Columbia- and Texel-sired lambs and did not differ significantly from either. 5) Total weight of lamb weaned per ewe mated is a composite trait that includes effects of ewe fertility and prolificacy and lamb survival and growth. The total weight of lamb weaned per ewe mated averaged 53.5 kg (118 lb) for Suffolk sires, 50.8 kg (112 lb) for Columbia sires, 49.4 kg (109 lb) for USMARC-Composite sires, and 47.6 kg (105 lb) for Texel sires. Because values of zero were assigned for this trait to open ewes or ewes that did not wean any lambs, the sire breed means had large standard errors and differences among sire breeds were not statistically significant. Additional data from this 3-year study will be used to quantify the effects of ram breed on postweaning growth potential, leanness, muscling, carcass yield, and carcass value of crossbred market lambs. When complete, data from this study should enhance the development of terminal crossbreeding systems and improve the efficiency of commercial lamb production.