Dissertation - Open Access
Doctor of Philosophy (PhD)
Christian A. Dinkel
A computer model was developed to evaluate the energetic efficiency of postweaning beef production of various biological types of cattle fed rations with different energy densities. In Section I, a mathematical model was developed to estimate voluntary feed intake for growing cattle from weaning to slaughter. The mathematical model included effects of differences in energy density and crude fiber content of the ration and in breed and degree of maturity of cattle on feed intake. When gastrointestinal tract distension controlled feed consumption, the primary factors determining feed intake were (1) rate of excretion of digesta, (2) rate of digestion, (3) dry matter digestibility, (4) gut fill, (5) breed of cattle and (6) degree of maturity of cattle. When feed intake was controlled by chemostatic and/or thermostatic mechanisms, the dry matter consumption was determined by physiological demand for energy, which varied with age and breed of animal. Data from the literature and from Bond (personal communication) were utilized to develop necessary equations. A computer program is available which estimates voluntary feed intake tor various breeds of cattle of different degrees of maturity fed various diets. In Section II, the effect of protein level in the diet and degree or maturity of the cattle on the coefficient of metabolizable energy utilization for fattening (kf) were evaluated. This coefficient indicates the percent of metabolizable energy retained as body tissue. Data from Peterson et al. (1973) were utilized to develop a multiple curvilinear regression equation for adjusting kf values recommended by A.R.C. (1965). The results of this study indicate that both degree of maturity of the cattle and protein level in the diets influenced the kt values. As cattle matured, kf value decreased. Both percent protein and calorie-protein ratio had nonlinear effects on kf values. In Section III, mathematical equations for estimating physical and chemical composition of steers of different biological types fed various diets were developed. Thus, the calorific value of live weight gain was also measured. All dependent variables of the equations were traits measurable prior to slaughter. Physical composition of live weight was divided into empty body weight and gut fill. Empty body weight was further divided into eight subcomponents according to the similarity of chemical composition within each component. Regression analyses were used to estimate gut fill and eight subcomponents of empty body. Regression equations for estimating chemical composition or each subcomponent of empty body were developed utilizing data from the literature. A computer program is available which predicts the physical composition, chemical composition and calorific value of live weight gain of steers for different biological types of cattle fed on various diets. In Section IV, a computer simulation was made (1) to estimate the energetic efficiency of postweaning beef production from four breed groups, (a) Jersey, (b) Hereford-Angus, (c) Dairy Shorthorn and (d) Holstein; (2) to evaluate the optimum time of slaughter for each breed type and (3) to evaluate the effect of slaughter at ages other than optimum time on energetic efficiency or beef production. The computer model included information from Sections I and II of this study and from N.R.C. (1976) and A.R.C. (1965) recommendations. Simulated results indicated larger breeds tended to reach the optimum time of slaughter at older ages and heavier weights than smaller breeds. Slaughtering cattle at ages other than optimum were evaluated in terms of energetic efficiency. Four ways of determining slaughter ages were used, (1) slaughter at simulated breed optimum age; (2) slaughter at various constant ages; (3) slaughter at a constant degree of maturity and (4) slaughter at a constant weight. Slaughter at a constant weight was least efficient and slaughter at a constant age was intermediate between slaughter at optimum age and s1aughter at constant weight. Slaughter at a constant degree of maturity was second in efficiency only to slaughter at breed optimum age. For practical application it will be necessary to estimate mature weight of young cattle. Further study will be necessary to develop accurate predictions of mature weight from early performance of the animal and its pedigree.
Library of Congress Subject Headings
Beef cattle -- Feeding and feeds
Cattle -- Carcasses
Beef cattle -- Weight
South Dakota State University
Song, Hoon, "Mathematical Models of Postweaning Growth, Feed Intake and Carcass Composition of Beef Cattle" (1976). Electronic Theses and Dissertations. 5545.