Paper-Lecture36 - E F F E C T O F H A Y TO G R A 1 N R A T...

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EFFE'CT OF HAY TO GRA1N RATIO ON UTILIZATION OF METABOLIZABLE ENERGY FOR MILK PRODUCTION BY DAIRY COWS 1 C. E. COPPOCK, ~ W. P. FLATT, AZ;D L. A. MOORE Energy Metabolism Laboratory, Dairy Cattle Research Branch, Animal tlusbandry :Research Division, Beltsvil]e, Maryland AND ~\r E. STEWART University of Maryland, College Park SUMMARY 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 covarianee analysis. ¥Vhen the maintenance requirement was assumed to be 131 keal ME/kg ~/~, and tissue gain or loss was adjusted to zero balance using the factors 1.61 keal ME/kcal tissue gain and 1.43 kcal ME/kcal tissue loss, the mean effieieneies of' converting the available ME to milk were 65, 61, and 54% (P < .05) for rations A, B, and C, respectively. Although some studies (15, 17) have shown no superiority for the estimated net energy (ENE) system over the total digestible nu- trient (TDN) system, when comparing forages and mixed rations for milk production, recent reports (20, 29) indicate that the ENE system more accurately predicts the actual response. No satisfactol T explanation hag been offered for the lower lactation response of cows fed TDN from forages, in contrast to those ani- nmls fed equal TDN from mixed rations. Since the basic differences between TDN and metabolizable energy (ME) are the deductions for methane and to some degree urinary en- ergy losses, and these have been shown to be sinfilar for forages and mixed rations (4, 27), the nmjor difference in the productive value Received for publication June 17, 1964. 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. Al132 Con- tribution No. 3586 of the Maryland Agricultural Experiment Station, Department of Dairy Science. ~Ralston-Purina :Research Fellow, 1960-61. Present address: Animal Husbandry Dept., Corne]l University, Ithaca, New 5York. for milk production of forages and mixed ra- tions nmst lie in the relative utilization of the ME from the respective rations. Metabolizable energy was used in this study because it is a distinct entity which can be measured directly without the empirical assmnptions of' the TDN system. Blaxter (4) has postulated that the efficiency of utilization of ME for lactation depends upon the relative proportion of volatile fatty acids (¥FA) in the rumen. The hay-to-grain ratio
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Paper-Lecture36 - E F F E C T O F H A Y TO G R A 1 N R A T...

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