BREED COMPARISONS AND TRENDS FOR EWE PRODUCTIVITY AND LAMB GROWTH TRAITS IN SHEEP MANAGED AS CONTEMPORARIES IN A WESTERN RANGE SYSTEM

Authors: Leeds, Timothy - Tim; Lewis, Gregory

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/21/2006
Publication Date: 5/30/2006
Citation: Leeds, T.D., Lewis, G.S. 2006. Breed Comparisons and Trends for Ewe Productivity and Lamb Growth Traits in Sheep Managed as Contemporaries in a Western Range System. Proceedings of the Western Section of the American Society of Animal Science. 57:86-89.

Interpretive Summary: Profitability of commercial Western range production systems is largely influenced by ewe productivity and growth of the lambs to weaning. Traits such as ewe fertility, litter size at birth, litter size at weaning, and litter weight weaned will respond to traditional selection; however, the lowly heritable nature of these traits limits their expected response to selection. As breeding objectives evolve in response to changing market signals, commercial producers have the opportunity to enhance profitability by capitalizing on breed diversity among Western white-faced ewes. Before a producer can objectively identify the ewe breed that is adapted to Western range management and best matches his or her breeding objectives, performance data that allows valid comparisons among breeds must be available. The primary objective of these analyses was to provide producers with performance data for four Western white-faced breeds (Columbia, Polypay, Rambouillet, and Targhee) managed as contemporaries in a spring (shed) lambing, summer mountain grazing, and 120-d weaning production system. From these data, producers can make statistically valid breed comparisons and identify the breed that maximizes their profit potential.

Technical Abstract: Ewe productivity and lamb growth traits are economically important for commercial sheep production systems; thus our objectives were to utilize retrospective data to characterize trends in performance and quantify breed differences for these trait types. Data were from purebred Columbia, Polypay, Rambouillet, and Targhee ewes and lambs from 28 yr of production beginning in 1978 at the U.S. Sheep Experiment Station near Dubois, ID. All breeds were managed for spring (shed) lambing, summer mountain grazing, and 120-d weaning. Generic selection practices throughout generally emphasized increased litter weight weaned. Data were analyzed using general linear and mixed models to test for fixed effects of breed, age of dam, year, types of birth and rearing, lamb gender, and breed×year interactions and the random effect of band (summer grazing). Breed least squares means (± SE) from 1978 for Columbia, Polypay, Rambouillet, and Targhee were, respectively: number born alive per ewe lambing: 1.33 ± 0.04, 1.75 ± 0.06, 1.46 ± 0.03 and 1.35 ± 0.03; birth weight (kg) of live lambs: 4.3 ± 0.07, 3.6 ± 0.09, 4.1 ± 0.05, and 4.2 ± 0.06; number weaned per ewe lambing: 1.19 ± 0.05, 1.47 ± 0.06, 1.31 ± 0.04, and 1.24 ± 0.05; litter weight (kg) weaned: 44.4 ± 1.6, 46.1 ± 2.2, 39.3 ± 1.4, and 40.3 ± 1.6. Breed least squares means (± SE) from 2005 for Columbia, Polypay, Rambouillet, and Targhee were, respectively: number born alive per ewe lambing: 1.54 ± 0.04, 1.70 ± 0.04, 1.52 ± 0.03 and 1.49 ± 0.03; birth weight (kg) of live lambs: 4.8 ± 0.08, 4.2 ± 0.04, 4.6 ± 0.05, and 4.6 ± 0.07; number weaned per ewe lambing: 1.48 ± 0.06, 1.58 ± 0.05, 1.43 ± 0.05, and 1.42 ± 0.05; litter weight (kg) weaned: 64.1 ± 1.8, 60.9 ± 1.6, 55.7 ± 1.6, and 56.8 ± 1.8. Coefficients for regression of trait least squares means on year were positive and different from zero (P < 0.05) for these traits in most breeds. Results of these analyses document progress in ewe productivity and lamb growth traits and provide Western range producers with the data necessary to make statistically valid breed comparisons.