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Influence of Environmental Adjustments on Heritability of Weaning Weight of Range Rambouillet Lambs

Texas Agricultural Experiment Station

Abstract

The least squares procedure was used to estimate the importance of factors affecting weaning weight of range Rambouillet lambs. Male lambs grew 7.2% faster than females. Single lambs grew 4.6% faster than twins raised as singles and 10% faster than twin lambs raised as twins. Lambs out of 2-year-old dams weighed 5.1 lbs. or 8% less than lambs out of mature ewes (3 through 7 years). Very old ewes weaned lambs weighing 7.6 lbs. or 11.7% less than ewes in years of peak production.

Heritability of weaning weight was estimated at 13.8% using unadjusted values. The extent to which the heritability can be increased by various methods of adjustment and calculations is reported. Correction for age of lamb made the greatest improvement in predicting the future breeding value of ewe lambs. In this study it was found that the use of a pooled regression coefficient (0.30 lb. per day) calculated by a simple average of the individual yearly regression coefficients gave results comparable to other procedures used.

¹ The authors acknowledge the assistance of T. C. Cartwright, Dept. of Genetics, Texas A. & M. College, and the staff of the Data Processing Center for assistance in making necessary calculations.

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				G. D. Snowder and L. D. Van Vleck Estimates of genetic parameters and selection strategies to improve the economic efficiency of postweaning growth in lambs J Anim Sci, November 1, 2003; 81(11): 2704 - 2713. [Abstract] [Full Text] [PDF]