Date of Award
Doctor of Philosophy
Harold J. Smith
Robert Dotson, J. T. Miles, Charles S. Hobbs
Selection is the most effective tool that a beef cattle breeder has at his disposal for the permanent genetic improvement of his herd. Improving the herd by selection is a slow, continuous process that requires much assiduity on the part of the breeder if satisfactory results are to be attained. The generation interval is much longer in cattle than in most other farm animals and multiple births, which increase the rate of progress from selection, are relatively unusual in cattle. Only a part of the superiority of the selected parents over the unselected herd average for a particular trait is transmitted to the offspring. Differences among animals due to environmental effects are not transmitted from generation to generation. Therefore, only a portion of the selection differential of the parents is realized in the offspring. It is necessary that accurate and independent estimates of en-vironmental factors of variation be obtained in order to precisely esti-mate heritability and, thereby, bring about expected genetic progress in improvement of economically important traits. At the time of this study, much of the research reported in the available literature concerned with the effect of various environmental factors on average daily gain from birth to weaning and on the type score at weaning of beef calves involved either uncontrolled or unmeasured factors. One approach to removing more of such variation would be to study repeated observations on the same cow, since this method removes genetic differences between cows. The objectives of this study were: 1. To obtain estimates on an intra-cow basis of the influence of sex of calf, year of birth, age of dam, reproductive status of the dam. season of birth, sex of the previous calf, weaning age, calving interval of the dam, average daily gain of the previous calf and the number of dry days of the dam on average daily gain from birth to weaning and on the type score of her calf at weaning. 2. To develop appropriate correction factors to adjust average daily gain and type score for environmental and developmental influences. 3. To calculate the heritability and repeatability estimates for average daily gain and type score.
Jamison, Haley Marshall, "Factors affecting intra-cow variation in production of beef cattle. " PhD diss., University of Tennessee, 1966.