Doctoral Dissertations

Date of Award

12-1977

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

J.B. McLaren

Committee Members

W.T. Butts Jr, J.H. Philpor, D.O. Richardson, R.R. Shrode

Abstract

The objectives of this study were to determine effects of cow weight, cow wither height, cow body volume, cow fat thickness, calf fat thickness, and cow size and shape indexes on 205-day weaning weight, adjusted wither height, approximate body volume, and size and shape indexes of calves. Indexes of size and shape were the result of principal-component analysis.

The data consisted of weight, body measurements and fat thickness measurements of 318 Hereford and 516 Angus cows and their progeny maintained at the Alcoa Farm, The University of Tennessee, Knoxville. Body measurements collected were wither height, body length, body depth and body width. Weaning weight and all body measurements collected on calves were statistically adjusted to a 205-day age basis and were adjusted for sex of calf effects with least-squares estimates of regression obtained directly from these data.

Principal-component analysis, a multivariate technique, was studied as a method to define animal size and shape. The first component for both cows and calves contrasted animals according to general size. It accounted for 56.2 and 46.9 percent of the total variation in cows and calves, respectively. The second component contrasted animals according to body shape. Total variation explained by the first two principal components was 72.5 and 67.2 percent for cows and calves, respectively.

All correlations among cow body measurements and measures of size, and among calf body measurements and measures of size were highly significant (P<.01). Adjusted 205-day weight and calf wither height were highly correlated (P<.01) with the cow measurements and measures of size. Calf volume was significantly (P<.01) correlated with the cow variables. Principal component indexes for size and shape of calves were generally highly correlated (P<.01) with the cow variables. Calf fat thickness was correlated (P<.01) with all cow variables except cow fat thickness, however the correlations were not as large as those with indicators of calf size.

Stepwise multiple regression analysis indicated that calf fat thickness and cow weight controlled the most variation in 205- day weaning weight. Effects of year, breed and cow age also were included in the model as discrete variables, as they were in all regression equations. Independent variables exhibiting the most pronounced effects on calf wither height were calf fat thickness and cow wither height. Calf fat thickness was indicated as the only significant effect on calf volume. Coefficients of determination (R2) of calf weight, wither height, and volume ranged from 39.7 to 42.9 percent. Independent variables with the greatest effects on calf size index were calf fat thickness, cow weight and cow shape index. Calf fat thickness and cow height were the first effects to enter the equation describing the regression of calf shape index on the cow variables. Coefficients of determination from analyses of calf size and shape indexes were 55.7 and 67.0 percent, respectively.

These analyses indicated that cow weight, cow wither height and calf fat thickness had the most pronounced effects on the measures of calf size and performance.

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