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Effect of Hay to Grain Ratio on Utilization of Metabolizable Energy for Milk Production by Dairy Cows¹

Energy Metabolism Laboratory, Dairy Cattle Research Branch, Animal Husbandry Research Division, Beltsville, Maryland

W. E. Stewart

University of Maryland, College Park

ABSTRACT

Indirect calorimetry was used in total energy balance trials with six mature, lactating, nonpregnant Holstein cows to study the utilization of metabolizable energy (ME) for milk production. An orthogonal set of 3 x 3 extra-period Latin-squares was used. The three rations fed contained 50% (A), 75% (B), and 100% (C) wafered alfalfa hay, based upon estimated net energy (ENE) values, and 50% (A), 25% (B), and 0% (C) of a mixture of corn meal and soybean oil meal. The rations were offered on an equal ENE basis.

More ME was required for milk plus maintenance from the all-alfalfa ration than was required from a ration of alfalfa and concentrate when the ME was regressed on milk energy. The treatment means were adjusted to a common milk energy output by covariance analysis.

When the maintenance requirement was assumed to be 131 kcal ME/kg^3/4, and tissue gain or loss was adjusted to zero balance using the factors 1.61 kcal ME/kcal tissue gain and 1.43 kcal ME/kcal tissue loss, the mean efficiencies of converting the available ME to milk were 65, 61, and 54%, (P < .05) for rations A, B, and C, respectively.

¹ Data taken from a thesis presented by C. E. Coppock in partial fulfillment of the requirements for the Ph.D. degree, University of Maryland, January, 1964. Scientific Article No. A1132 Contribution No. 3586 of the Maryland Agricultural Experiment Station, Department of Dairy Science.

² Ralston-Purina Research Fellow, 1960–61. Present address: Animal Husbandry Dept., Cornell University, Ithaca, New York.

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