Response of Lactating Cows to Free-Choice Feeding of Milled Diets Containing from 10 to 100% Concentrates

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Abstract
Four milled diets having hay-to-concentrate ratios of 90:10, 60:40, 30:70, and 0:100 were compared by feeding to groups of 6 first-lactation cows after the peak of lactation. Judged from all criteria, the 60:40 ratio resulted in the best performance. Cows obviously were unable to consume sufficient feed from the 90:10 diet to meet their energy requirements. Milk yield was depressed, especially during the first few weeks on trial, and the animals lost condition, although this was not reflected in significantly lower weight gains, due to apparent errors in estimate of live weight. In the 2 high-concentrate groups it was obvious from the over-conditioning of the cows that energy Intakes exceeded milk production ability. The milk fat percentage of the cows on the all-concentrate ration was depressed very markedly. No significant effect of diet on protein or SNF content of the milk was observed. For 6 wk before the trial all cows were fed the 30:70 diet and for the first 14 wk milk protein content of the cows continued on this diet was maintained, whereas that of the others fell slightly. The significance of this effect disappeared after the 14th wk. None of the diets appeared to have any deleterious effects upon the health cf the animals, with the exception of one suspected, but not positively diagnosed, case of laminitls.

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