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Principal Components for Cow Size and Shape

Texas Agricultural Experiment Station, College Station 77843

Abstract

Thirty-eight Hereford and 23 Charolais cows, 5 years or older, were maintained in drylot during the lactation (7 months) and postlactation (5 months) phases of a production cycle. Daily feed consumption was regulated to maintain all cows in similar fleshing conditions throughout the production cycle. Cows were weighed biweekly; average weights over the production cycle (12 months) were computed. Chest depth, hook width and body length were measured on each cow when the calves were weaned. Principal components of the matrix of correlations among the three linear measurements and average weight were computed. The first component, interpreted as an indicator of body size, accounted for approximately 75% of the generalized variance. The second component accounted for an additional 12 to 15% of the generalized variance and was interpreted as an indicator of body shape (e.g., endomorphic vs ectomorphic). The correlation between average cow weight and the first principal component was .93, supporting the common use of weight as a measure of cow size.

¹ Current address: Animal Science Department, Colorado State University, Ft. Collins 80521.

² Current address: Winrock International Livestock Research and Training Center, Route 3, Morrilton, AR 72110.