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Genetic Parameters of Some Performance Characteristics of Range Fine-Wool Ewes

Texas A&M University, College Station

Abstract

Production data obtained from a flock of range raised Rambouillet sheep were analysed to obtain estimates of certain genetic parameters concerned with total lamb and wool production. Only ewe lambs raised on the property and which had completed their lifetime performance between the years 1930 and 1966 were considered. A total of 1,330 animals were involved, although the number considered in any specific analysis was reduced from this due to early death losses or incomplete data. The influence of age of ewe is reported and follows the general pattern from earlier reports. Simple phenotypic correlations between the variables considered in the study are also reported. The majority of these coefficients were significant, but of low magnitude except in those cases where the variables represent alternative measures of the same characteristic.

Heritability estimates were calculated by the paternal half-sib and intra-sire regression of offspring on dam methods. Mean fleece weight was highly inherited with estimates of .58 and .52 by paternal half-sib and intra-sire regression methods, respectively. Comparable values for total wool production were .26 and .23. Several estimates were calculated for various measures of total lamb production or lamb production expressed as a function of the number of years in the flock. All of these yielded significant positive estimates ranging from .18 to .28. Genetic correlations were calculated by covariance analyses of paternal half-sib data. In general, negative relationships, but of low magnitude, were obtained between weaning weight and measures of total lifetime lamb production. The same calculations based on yearling weight were positive. There was a consistent negative relationship between fleece weight and all measures of fertility or total lamb production.

¹ Livestock and Forage Research Center, McGregor.

² Ranch Experiment Station, Sonora.

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