Effect Upon Lipid Metabolism of Feeding Alfalfa Hay or Concentrate Ad Libitum as the Sole Feed for Milking Cows

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Abstract
Ad libitum group feeding of only alfalfa hay was compared to only concentrate in an experiment with 6 Holstein and 6 Jersey cows. A double-reversal design with 5-wk periods was applied. Intakes of dry matter from the 2 feeds were equal with Holstein cows, but were higher on hay than on concentrate in the Jersey cows. All-concentrate feeding depressed the per cent and yield of milk fat in both breeds, but the responses were lower and more variable in the Jersey than in the Holstein cows. Reduced output of milk fat was due to a reduction in the amounts of all major fatty acids synthesized, but the magnitudes of the decreases was considerably less for the lower and unsaturated than for the higher saturated fatty acids. Increased outputs of certain unsaturated and odd-numbered fatty acids were found. All-concentrate feeding increased the amount of milk secreted, but outputs of milk energy were about equal on the 2 feeds. Concentration and yield of SNF and live weight gains were higher on concentrate.

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