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Working Maintenance as a Function of Live Weight in Dairy Cows, and its Bearing on an Energy-size Index of Lactation

Illinois Agricultural Experiment Station, Urbana, Illinois

ABSTRACT

Certain records (253) of feed intake, milk yield, and change in live weight give on analysis, DN'' = .129W^.60, where DN'' is pounds of digestible nutrients per day for working maintenance and W is live weight of the cow, in pounds. Of these 253 records, 172 show a gain in live weight and give DN'' = .369W^.45; 81 show a loss in live weight and give DN'' = .021W^.78. It is thought the latter group best warrants the method of analysis. It is concluded the results of the whole analysis are too variable and uncertain to be regarded as necessitating any change in Haecker's DN'' = .008W, for dairy cows in milk.

If it is accepted as fact that basal metabolism = KW^.73, the question is raised as to the soundness of assuming that, consequently, active tissue =K₁W^.73 working maintenance = K₂W^.73, or potential milking capacity =K₃W^.73.

The bearing of the working maintenance and live weight relation is discussed in comparison of four energy-size indexes or efficiency formulas. For practical utility as a biological measure of comparative dairy development preference is expressed for the formula FCM/IW in which FCM is milk energy yield for some suitable uniform period (such as the 3d-245th days) of the lactation, and IW (initial weight) is live weight of the cow at the start of the period.