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Milk Protein Synthesis as Affected by High-Grain, Low-Fiber Rations¹

Dairy Department, Michigan State University, East Lansing 48823

ABSTRACT

Thirty-six Holstein cows were fed the following rations in two trials which lasted 50 days each: A) forage ad libitum plus 1 kg concentrate per 3 kg milk; B) concentrate ad libitum plus 2.7 to 3.2 kg air-dry forage; C) B plus 7% partially delactosed whey, 1.25% NaHC0₃, and 0.5% MgO in the concentrate. Milk yields tended to be lower for B than A and C in Trial 1, though differences were not significant. Cows were earlier in lactation in Trial 2 than 1, and milk production did not differ between treatments. Protein concentrations in milk were higher for high-grain groups in both trials. Greater yields of milk protein (P < .05) resulted from high-grain feeding in Trial 2. Since the additives tended to increase milk fat and also shifted rumen volatile fatty acids towards patterns for normal rations, the increased milk protein was not dependent on increased ruminal propionate and was compatible with correction of the milk fat depression.

-Casein and ß-lactoglobulin accounted for the increase in milk protein, whereas milk serum albumins and "other nitrogens" decreased. Concentration of -lactalbumin was correlated 0.88 with milk production.

¹ Published with the approval of the Director of the Agricultural Experiment Station as Journal Article no. 4872.