Effects of Dietary Lipid and Protein on Growth and Nutrient Utilization by Dairy Calves at Ages 8 to 18 Weeks

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Abstract
Relationships between dietary lipid and protein were investigated with Holstein calves, 8 to 18 weeks of age. A 2-dimensional, central composite experimental design was used, with 5 levels each of corn oil and soy protein. Nine experimental rations, formulated by substituting combinations of corn oil from zero to 8% and soy protein from zero to 28% in a basal ration, were evaluated in a 10-week feeding period. Growth and feed consumption were recorded and ration digestibility was determined at 8, 13, and 18 weeks by indicator-ratio techniques. Multiple regression techniques, applied to the observed results, predicted that an optimal combination of 1.9% corn oil and 16.2% soy protein substituted in the basal ration would have resulted in maximal growth for the 10-week feeding period. Considering the contributions of the basal ration, maximal growth was predicted to occur with a ration whose dry matter contained 4.54 kcal/g of gross energy and 24.8% crude protein. When 18-week predicted nitrogen and energy digestion coefficients, body weight gains, and dry matter intakes were combined, 0.75 kg of digestible protein and 12.49 megcal of digestible energy/day were predicted to result in maximal growth of the 146-kg calf. Additions of corn oil up to 4% resulted in only a slight reduction in growth. At levels of oil above 4%, digestibilities of dry matter, energy and lipid were reduced, feed intake declined, and growth was inferior.