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Genetic and Phenotypic Parameters including Occurrence of Estrus in Rambouillet Ewe Lambs¹

Montana State University, Bozeman 59715

Abstract

Data from 384 Rambouillet ewe lambs were used to study birth weight, weaning weight, 18-month weight, grease fleece weight and incidence of estrus as ewe lambs. These data were analyzed by least squares analysis of variance and covariance and constants were fitted for type of birth, age of dam, feed treatment, year of birth, sire within year and birth date of lamb. The paternal half-sib variance and covariance components were used to estimate the heritabilities and correlations among the various traits. Age of dam significantly affected all traits studied and type of birth of the ewe significantly affected all traits studied except incidence of estrus as ewe lambs. The heritability estimates were 0.92, 0.14, 0.45, 0.31 and 0.15 for birth weight, weaning weight, 18-month weight, yearling fleece weight and incidences of estrus as ewe lambs, respectively. Birth weight, weaning weight and 18-month weight all had positive genetic correlation with incidence of estrus as a ewe lamb.

¹ Contribution from the Montana Agricultural Experiment Station, Journal Series No. 202. The authors express their appreciation to Dr. E. P. Smith and Mr. R. Stewart for their assistance in the statistical analysis of these data and Dr. A. S. Hoversland for his contribution in collection of these data.