The protein requirement of the ruminant calf. II. Further studies on the effect of protein content of the concentrate mixture on the performance of calves weaned at an early age

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Abstract
1. Eighty-four Friesian heifer calves were used in two experiments (Experiments 4 and 5) to study the protein requirement of the ruminant calf to 12 weeks of age. The calves were weaned at 5 weeks of age and given a concentrate containing one of several protein levels, together with hay and water.2. In Experiment 4, the effect of changing the protein content of the concentrates at 8 weeks of age under ad libitum feeding conditions was studied. A concentrate containing 20·6% crude protein (air-dry basis) tended to promote more rapid weight gains in calves to 8 weeks than a similar concentrate with 12·1% crude protein. Following the change in diet at 8 weeks, both groups of calves given the low-protein diet gained weight at similar rates in the period 8–12 weeks, irrespective of the protein level to 8 weeks. During the period 8–12 weeks calves given the high-protein diet, after receiving a low-protein diet to 8 weeks, tended to gain weight at a faster rate than those given the high-protein concentrate throughout. After adjustment for differences between treatment groups in mean concentrate consumption and mean live-weight at 8 weeks, the live-weight gain from 8 to 12 weeks was significantly greater in calves given the high-protein diet after 8 weeks.3. In Experiment 5, a significantly lower growth rate was obtained when concentrate intake was restricted to a maximum of 2 kg./day than when given ad libitum. Calves given the concentrates containing 15·9% or 20·6% crude protein gained weight significantly faster than those given the concentrate containing 12·1% crude protein, at both levels of feeding, after live-weight gain was adjusted for differences between treatment groups in mean food consumption and live-weight at 1 week.4. It is concluded that no advantage is obtained by giving a concentrate containing more than 15·9% protein to Friesian heifer calves weaned at 5 weeks of age. The results indicate clearly the importance of an adequate supply of energy in the diet of the ruminant calf if maximum live-weight gain is to be achieved.