Abstract
Data were obtained from 54 neonatal lambs that had been removed from their dams at 1 to 2 days of age and individually fed two dietary fat levels, 15 and 30%, and within each fat level, one of three protein levels, 15, 23 and 30% for 28 days. Representative lambs were slaughtered at birth and at 4 weeks of age for energy and nitrogen retention data. Dietary protein level significantly affected weight gain, feed: gain ratio, energy and protein efficiency ratios and body protein levels; whereas dietary fat level had no significant effect on any of these measurements. Lambs fed diets that contained 15% protein gained slower and were less efficient in energy utilization than lambs fed either medium or high protein diets. However efficiency of protein utilization favored lambs fed diets that contained 15% protein rather than lambs fed diets with 23 or 30% protein. The curvilinear relationships between heat production, average daily gain and energy retention on metabolizable energy and dry matter intakes were significant, indicating that the efficiency of metabolizable energy of a diet used for growth, changes as the level of feed intake changes. The fasting metabolic rate of 3-week-old lambs, calculated from the regression of heat production on metabolizable energy intake, was 91.5 kcal/W.75kilogram• The metabolizable energy requirement for maintenance of young lambs at zero weight gain was 117.2 kcal/W.75kg, whereas, the net energy for maintenance at zero weight gain was 107.2 kcal/W.75kg, thus the heat increment at maintenance was 10 kcal/W.75kilogram• Protein and net energy requirements were determined by regression analyses. Net energy values of the milk replacer for growth and maintenance were also determined. The curvilinear relationship of weight gain on gross energy intake or on protein intake was significant indicating that the optimum protein: calories ratio changes as rates of gain change. From the data it was concluded that for reasonable growth and development (0.2 to 0.3 kg gain/day), young lambs required a minimum of 250 to 300 g of milk replacer dry matter containing 24 to 26% protein and approximately 20 to 25% fat. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science.