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A Study of Some Aspects of Lifetime Production in Targhee and Columbia Sheep¹

Montana State University, Bozeman 59175

Abstract

Data from 742 Targhee and 411 Columbia ewes born between 1950 and 1962 were studied for their lifetime lamb and wool production. No adjustments of any kind were made on the data. Least-squares analysis of variance was used to study the effect of type of birth (single vs. twin) of the ewe and her sire and the interaction between type of birth of the ewe and her sire on the number of multiple births, number of lambs born, number of lambs weaned, total pounds of lambs weaned, total pounds of fleece, and average annual lifetime production. In the Targhees either the type of birth of the ewe, the type of birth of the ewe's sire or the interaction between the type of birth of the ewe and her sire significantly affected all traits except the average number of lambs born. In Columbia, an effect of type of birth was observed for only five of the traits. However, the data for both the breeds tended to follow a similar trend.

Phenotypic correlation coefficients between 14 traits related to lifetime production were studied separately for each breed. In addition to the significant correlation between different traits most of the traits were observed to be significantly related to the weaning and yearling weight in both the breeds. Type of birth of ewe's sire was observed to be significantly related to the lamb production traits in Targhee. No negative phenotypic correlations between lamb and wool production traits were observed in either of the breeds.

Heritability estimates for nine traits related to lamb and wool production were studied by the paternal half-sib and daughter-dam regression methods. The heritability estimates reported ranged from 0.0 to 0.50 for the reproductive traits and from 0.0 to 0.34 for the fleece traits. In the Targhees negative genetic correlations between lambs born and fleece weight were observed, but in the Columbias the correlation was positive. The study suggested that the selection of rams and ewes born as twins is expected to enhance the lifetime production of their female progeny.

¹ Contribution from the Montana Agricultural Experiment Station, Journal Series No. 369. The authors express appreciation to Dr. E. P. Smith and Mr. V. R. Stewart for their assistance in the statistical analysis of these data.