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Ten attributes representing various body and. carcass measurements of beef steers were considered for statistical analysis. The slaughter data were obtained from an experiment conducted at Blacksburg, Virginia, by members of the Animal Science Department of the Virginia Polytechnic Institute, described by Kelly et al. (1968). The objective of the study was to obtain estimates of the effects of slaughter time (age), and of the energy level of the ration fed, on the body proportions and carcass composition of beef steers from approximately 7 to 30 months of age. The nutritional regimens used were: Ration I - maintenance; Ration II - full feed of hay; Ration III - limited concentrate plus full feed of hay; Ration IV - full feed of a fattening ration. According to the design of the experiment, the linear model included the general mean, the effects of slaughter time, breed, trial, slaughter time by trial interaction and slaughter time by breed interaction, and an error term. The first part of the investigation dealt with the analysis of variance of the percentage hot carcass to determine whether the effects of breed and trial were significant. In the second part, only the general mean, the slaughter time effect, and an error term were included in the model. When the slaughter time was found significant or highly significant, the sum of squares due to slaughter time was divided into regression components to determine which polynomial regression model best described the relationship between the body component mean and age. The results of the statistical analyses were as follows: 1. Breed and trial effects on the percentage hot carcass were insignificant in all but ration II, in which trial was significant. 2. Slaughter time by trial interaction effect was significant in all rations; slaughter time by breed was not. 3. The percentage hot carcass behaved in a parabolic manner with age, which was concave upward at lower planes of nutrition; the pattern changed to cubic at higher planes. 4. Age had no effect on the mean empty-body weight with steers on ration I; the effect was linear on ration II; quadratic on rations III and IV. Similar growth pattern was obtained for the percentage meat. 5. The percentage of front quarter to total carcass increased proportionately with age in all rations; the opposite trend was obtained for the percentage hind quarter. 6. The relationship of weight of the head, expressed as percentage of the live weight, with respect to age or slaughter time was linear with positive slope on rations I and II and negative on rations III and IV. 7. The percentage moisture in the meat showed a quartic regression with age on ration I presumably due to random fluctuation of the means. For rations II and III, the relationship was quadratic and concave downward; for ration IV, it was linear with negative slope. 8. The percentage crude protein and the percentage ash behaved similar to that of the percentage head, while opposite pattern was obtained for the ether extract. / Ph. D.

Under the conditions of this study, the following conclusions seemed justified: 1. Cud inoculations did not improve rate of growth or efficiency of feed utilization in calves through four months of age. Consumption of hay was not materially increased by cud inoculations. 2. Thus. it is concluded that cud inoculation is of no economic value under practical calf raising conditions. 3. Calves restricted in grain feeding did consume more hay than unrestricted calves; however, the increase was not great. Efficiency of feed utilization, as measured by the pounds of T. D. N. consumed per pound of gain was essentially the same for calves on a grain:hay ratio of 1:2 (restricted grain feeding) as those on a 1:1 grain:hay ratio (unrestricted grain feeding). 4. Skeletal growth, as determined by height at withers, was adversely affected by restriction or grain in the feeding program. 5. Calves fed one pound of whole milk per ten pounds of body weight daily up to 60 days of age, and a simple grain ration made satisfactory growth when grain was fed free choice (with a four-pound daily maximum) and hay of average or better quality was fed free choice. 6. Thus, it is indicated that a substantial monetary saving in the raising of herd replacements may be affected by the use of a simple grain ration instead of high-priced commercial calf mixtures. / Master of Science