Results are reported from an experiment examining the effects on the growth of the pre-ruminant calf of diets containing a range of protein: energy ratios fed at two rates. Groups of three Friesian bull calves were allocated to each of six milk-based rations containing either 15.7, 18.1, 21.8, 25.4, 29.6, or 31.5 protein on a dry matter basis and fed adequate energy for growth rates of 830 gjday. The same diets, except the 29.6 protein ratio, were also fed to five groups of three calves receiving energy intakes sufficient for growth rates of 610 g/day, The comparative slaughter procedure was used to assess treatment effects after a 49-day trial period. Both protein and feeding levels markedly affected the gains of body weight, protein, and fat, but energy gains were affected by dietary protein content only at the low feeding level. Estimated digestible protein requirements for maximum body weight gains were 166 #xB1; 13 gjday and 236 #xB1; 19 gjday at the low and high feeding levels respectively and were 204 #xB1; 19 g/day and 274 #xB1; 19 gjday for maximum protein gains at the same respective feeding levels. Faecal nitrogen was poorly related to dry matter intake (r = 0.48) and unrelated to feeding level, dietary protein percent, or calf age. Biological values decreased linearly with increased dietary protein level.
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