Doctoral Dissertations

Date of Award

6-1980

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

Robert R. Shrode

Committee Members

J.B. McLaren, H.V. Shirley, R.S. Dotson

Abstract

Data were obtained at weaning from 1521 Angus calves sired by 145 bulls during a period of ten years (1969 to 1978). Yearling data were obtained from 1388 Angus calves sired by 135 bulls during a period of nine years (1970 to 1978). The calves supplying these data were raised at the University of Tennessee Plateau Experiment Station, Crossville, Tennessee. The traits recorded on each animal at weaning (average age, 230 days) and at post-weaning (average age, 385 days) were Average Daily Gain, Body Weight, Body Length, Hip Height, Hip Width, Fat Thickness, Hide Thickness, Heart Girth, Condition Score and Type Score.

Post-weaning feeding was on a relatively high forage, low concentration ration. Heifers were fed at a restricted level, as compared to bulls to produce an average daily gain of approximately one pound per day, with limited fat production.

All records were adjusted by using constants obtained by least-squares procedures to remove variation due to differences in age of calf, sex of calf and age of dam. Nested within-year analyses were performed. One model was used to obtain estimates of components of variance due to sire differences, and another model was used to obtain estimates of components of variance due to dam differences. Analyses by the second model were performed after adjusting the data to remove variation due to sire and year differences. The estimate of the component of variance due to differences in maternal influence was calculated as the difference between the estimate of the component of variance due to total variation between dams and the estimate of the component of variance due to sire differences.

Results showed maternal influence on average daily gain (ADG) to weaning in bulls to be greater than that on ADG of heifers. Sire differences in all but two traits, average daily gain and hide thickness, were significant (P<0.01) at post-weaning, but at weaning, sire differences were significant (P<0.01) in only four traits: average daily gain, heart girth, condition score and type score. Differences between sires were responsible for a significant portion of the variance in body weight of both bull (P<0.01) and heifer calves (P<0.01), and bull calves were significantly (P<0.01) heavier than heifer calves. The male data were responsible for the increases in maternal variance percentages from weaning to post-weaning with respect to all but two traits in males, average daily gain and fat thickness which showed the expected decrease. These two traits are obviously directly affected by nutrient supply. The differences between males and females with respect to changes in relative importance of maternal influence from weaning to post-weaning indicate that females, during the post-weaning period, tend to reflect differences in their individual potential for growth more than do males which, apparently, reflect persisting maternal effects during the post-weaning period. In general, maternal variance percentages are greater in females at weaning and greater in males at post-weaning. Maternal variance is of considerable magnitude in several traits both at weaning and post-weaning. However, specific recommendations as to adjustments to remove maternal variance are not justified at this time.

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