The protein requirement of the ruminant calf. I. 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. Three experiments are reported, in which a total of seventy-two calves were weaned at 3 or 5 weeks of age and given concentrate mixtures containing either 19·2% or 11·9% crude protein, together with hay and water up to 12 weeks of age.2. The performance of cross-bred calves weaned at 3 weeks of age and given concentrates ad libitum was significantly greater when the high-protein concentrate was used in Experiment 1.3. In Experiment 2, in which Friesian heifer calves were weaned at 5 weeks and given concentrates ad libitum, the level of protein in the concentrates had no significant effect on live-weight gain from birth to 12 weeks. However, there was a tendency for the performance of calves given the concentrate containing 11·9% crude protein to be slightly inferior up to the age of 8 weeks.4. When concentrate intake was restricted to 2 kg./day in Experiment 3, in which Friesian heifer calves were weaned at 5 weeks of age, the live-weight gain was significantly greater when the higher level of protein was given.5. Daily increases in height at withers, heart girth and belly girth tended to be greater in all instances when the concentrate containing 19·2% crude protein was given, but significant differences between treatments occurred only in Experiment 3 for increase in heart girth and belly girth.6. It is apparent from the results that the calf weaned at an early age needs to be given a concentrate containing more than 11·9% crude protein if maximum live-weight gain is to be achieved up to 8 weeks of age. The optimum protein content of the concentrate after this age seems to depend on the level of concentrate feeding. The relationship between energy and protein in determining production is discussed.