Author
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Snowder, Gary |
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KNIGHT, ARLIN - FORMER ARS |
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Van Vleck, Lloyd |
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Kellom, Thomas |
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BROMELY, C. - UNIV OF NEBRASKA |
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Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/6/2000 Publication Date: 5/12/2001 Citation: Snowder, G.D., Knight, A.D., Van Vleck, L.D., Kellom, T.R., Bromley, C.M. 2001. Usefulness of subjective ovine milk scores. II. Genetic parameter estimates. Journal of Animal Science 79:869-876. Interpretive Summary: Genetic parameters for a subjective milk score given to ewes within 24 hr of parturition were estimated to determine the usefulness of milk score as a selection trait to improve milk production which is a component of total litter weight weaned. Heritability of milk score and the genetic correlation of milk score with litter weight weaned were estimated separately for four breeds; Rambouillet, Targhee, Columbia and Polypay. Litter weight weaned was the total weight of lambs weaned at approximately 120 d of age under western range production. Heritability estimates for milk score at first parity were moderate and similar among breeds. Estimates of heritability for second parity milk score were moderate. Milk score at first or second parity was genetically correlated with milk score records at maturity (third parity and greater). Milk score and litter weight weaned were genetically correlated at first or second parity in Rambouillet and Targhee breeds but not in the Columbia and Polypay breeds. Estimates of genetic correlations of annual lifetime milk score records with litter weight weaned were high for all breeds. Milk score as measured at first or second parity may be a good predictor of future potential milking ability. However, milk score can be used as a selection trait to improve maternal ability for increasing litter weight weaned. The need for increasing ewe milking performance and lamb growth rate at first parity in commercial range sheep production systems may be addressed by selection for milk score at first parity. Technical Abstract: Genetic parameters for subjective milk scores given to ewes within 24 hr of parturition were estimated to determine usefulness of milk score as a selection trait to improve milk production, a component of total litter weight weaned. Heritability of milk score and genetic correlation of milk score with litter weight weaned were estimated separately for Rambouillet, Targhee, Columbia and Polypay. Litter weight weaned was the total weight o lambs weaned at approximately 120 d of age under a western range production system. Heritability estimates for milk score at first parity were moderate and similar among breeds(range 0.18 to .32). Heritability estimates adjusted for a binomial distribution of milk scores at first parity were high for all breeds. Estimates of heritability for second parity milk score were moderate (range = 0.19 to 0.32). Milk score at first or second parity was genetically correlated with milk score records at maturity (third parity and greater, range = from 0.69 to 1.00). Milk score and litter weight weaned were genetically correlated at first or second parity in Rambouillet and Targhee but not in Columbia and Polypay. Estimates of heritability for lifetime records for milk score ranged from 0.16 to 0.26 across breeds. Estimates of genetic correlations of annual lifetime milk score records with litter weight weaned were high for all breeds. Repeatability estimates for milk score were similar across breeds. Milk score measured at first or second parity may be a good predictor of future potential milking ability. Milk score can be used to improve maternal ability for increasing litter weight weaned. Increasing ewe milking performance and lamb growth rate at first parity in commerical sheep production systems may be addressed by selection for milk score. |
