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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Genetics and Animal Breeding » Research » Publications at this Location » Publication #172010
Title: GENETIC RELATIONSHIP BETWEEN MILK SCORE AND LITTER WEIGHT FOR TARGHEE, COLUMBIA, RAMBOUILLET AND POLYPAY SHEEP

Author
item SAWALHA, R. - UNIV. OF NEBR-LINCOLN
item Snowder, Gary
item KEOWN, JEFFREY - UNIV. OF NEBR-LINCOLN
item Van Vleck, Lloyd

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2005
Publication Date: 4/1/2005
Citation: Sawalha, R.M., Snowder, G.D., Keown, J.F., Van Vleck, L.D. 2005. Genetic relationship between milk score and litter weight for Targhee, Columbia, Rambouillet and Polypay sheep. Journal of Animal Science 83:786-793.

Interpretive Summary: Subjective measures of milk score in a study of measures on 5,807 ewes of four sheep breeds at the U.S Sheep Experiment Station were found to be positively genetically correlated from one parity to another. Similarly, litter weights at 70 d were positively correlated across parity. Those results show that selection for higher milk score and greater litter weight at 70 d could be effectively initiated as early as the first parity measurements. Milk scores and litter weights at 70 d were generally positively genetically correlated for all four sheep breeds. Sheep producers could effectively utilize the subjective milk scores to indirectly select for favorable response in litter weight at 70 d or to improve the accuracy of genetic evaluation for litter weights at 70 d for Targhee, Columbia, Rambouillet and Polypay sheep.

Technical Abstract: This study was conducted to evaluate the relationship between milk score (MS) and litter weight at 70 days (LW) for four sheep breeds in the U.S. Milk score is a subjective measure of milk production used to assess milk production of range ewes where milk yield cannot be quantitatively determined. Variance components for MS and LW were estimated for the Targhee, Columbia, Rambouillet and Polypay breeds. Data collected from 1990 through 2000 at the U.S. Sheep Experiment Station in Dubois, ID were analyzed with an animal model using REML. Number of MS and LW records was 13,900 for 5,807 ewes. Records were grouped according to parity as: first, second, and greater (mature), and all records (lifetime). Estimates of heritability for MS ranged from 0.05 to 0.18 for first, from 0.01 to 0.27 for second, from 0.05 to 0.10 for mature and from 0.08 to 0.13 for all parity groups. Estimates of genetic correlation between MS at first and second parities ranged from 0.74 to 1.00. Similarly, mature MS was estimated to be highly correlated genetically with MS at first (0.83 to 1.00) and at second (0.60 to 1.00) parities which suggests that additive genetic value for milking ability at maturity could be evaluated as early as the first parity. Heritability estimates for LW ranged from 0.00 to 0.18 over all breeds and parity groupings. The estimates of genetic correlation between LW at first and second parity groups ranged from 0.43 to 1.00. Estimates of genetic correlation between LW at first or second parity with mature LW were mostly high and positive except at first parity for Targhee (-0.10) and Polypay (0.14) at first parity. Litter weight for mature ewes could be improved by earlier selection at first or second parity. Estimates of genetic correlation at first parity between MS and LW were near unity (1.00) for Rambouillet and Polypay, and close to zero for Columbia and Targhee. For the second parity, estimates of genetic correlation between MS and LW were positive and moderate for Rambouillet and Polypay but more variable for Columbia and Targhee. Estimates of genetic correlations between MS and LW were always positive. Although estimates are variable, the average of the estimates of genetic correlations suggests that LW could be improved by selecting ewes for favorable milk scores.