Date of Award
Doctor of Philosophy
L.M. Josephson, R.L. Murphee, D.O. Richardson
Data collected over a period of four years from 120 bulls and 103 heifers from a Polled Hereford herd maintained at one location, and 291 bulls and 292 heifers from an Angus herd maintained at another location were utilized in studies of relationships among measures of growth, size and body composition. All analyses were conducted separately for each location-sex subgroup. Data were collected at three times of observation. At preweaning (approximately four and one-half months of age) and weaning (approximately seven and one-half months of age) the following variables were recorded; age, live weight, body length, heart girth, subjective condition score, ultrasonic fat thickness and hip width. At yearling age (approximately 13 months) three variables were recorded: birth-to-yearling average daily gain, postweaning average daily gain and condition score. The primary objective of the study was the prediction of the yearling traits utilizing independent predictors recorded at preweaning and weaning.
Principal-components (PC) analyses were conducted on variables recorded at preweaning and weaning, using weight, length, heart girth, hip width and condition score. The first principal component (PCl) provided a means of ranking animals according to overall size with positive coefficients for all variables. Other components provided indexes which elucidated differences in shape. Transformed variables were calculated for each component for each individual.
Two types of stepwise multiple regression equations, using either the variables collected at preweaning and weaning (Model I) or the transformed values from PC analyses (Model II), were constructed to predict the three yearling traits. All equations were fitted on a within-year-and-sire basis, and age was the first independent variable entered in every case. R2 values were highest for birth-to-yearling gain (50 to 75 percent) followed by condition score (15 to 50 percent) and postweaning gain (below 16 percent). Condition score and length were generally the best predictors to be used in addition to age and weight. The most valuable components were PCl (overall size) and PC2 (a contrast of condition against length and width). Weaning variables generally resulted in larger R2 values than did preweaning variables.
Relationships were such that animals with high rates of gain tended to be heavy in weight, long-bodied and thin at preweaning and weaning with positive values for PCl and negative values for PC2. Those with high yearling condition tended to be heavy, short-bodied and high in condition with positive values for both PCl and PC2.
It appears from these results that measures of skeletal size and body fatness are of value in predicting future performance, presumably by making for a more accurate appraisal of stage of maturity.
Hammack, Stephen Paul, "Calfhood weights, body measurements and estimates of body composition vs.criteria of overall size and shape for predicting yearling performance in beef cattle. " PhD diss., University of Tennessee, 1973.