Effects of Various Hay-Concentrate Ratios on Nutrient Utilization and Production Responses of Dairy Cows. I. Relationships among Feeding Level, Predicted Producing Ability, and Milk Production

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Abstract
Hay and concentrates in 4 ratios (75:25, 55:45, 35:65, 15:85) were fed to lactating cows for 182 days, starting 64 days after parturition, in isodynamic amounts above individual maintenance requirements at each of 3 feeding levels (high, medium, low). Thirty-six Holsteins were divided into high-, medium-, and low-producing groups, and 3 cows, 1 of each group, were placed at each of the hay: concentrate-feeding level positions. For each cow the total feed energy requirement for production was predetermined and partitioned into decreasing weekly quantities. Feeding was based on net-energy recommendations for maintenance and production. The differences in the estimated net energy (ENE) available for milk production at the 3 feeding levels were much greater than the corresponding differences in fat corrected milk (FCM) production, which indicated that the ability of the animals exerted a greater influence upon production than did the intensity of feeding. Production in the preliminary period was highly correlated with that in the experimental period. The production response to full feed during the post-experimental period indicated a relation to the magnitude of production in the preliminary period. Weight changes during the initial 5 weeks of the experimental period were closely related to diet, but thereafter, particularly at the lower feeding levels, were largely independent of the ration.