HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gaines, W. L. Articles by Overman, O. R. Search for Related Content PubMed Articles by Gaines, W. L. Articles by Overman, O. R.

Interrelations of Milk-Fat, Milk-Protein and Milk-Energy Yield

Illinois Agricultural Experiment Station, Urbana, Illinois

ABSTRACT

The data examined consist of the 305-day partial lactation yields of 130 cows with respect to milk fat, milk protein and milk energy. The yields were determined by continuous milk weights and complete chemical analysis of 3-day samples at 5-week intervals.

Where only the milk yield and fat yield are known milk energy yield may be estimated more accurately (r = .985) than can protein yield (r = .755). The accuracy of estimate of energy yield from milk and protein yield is intermediate (r = .832). These correlations are between actual and estimated yields, at a given milk yield.

While the correlation between fat percentage and energy per kilogram of milk is much higher (r = .985) than that between protein percentage and energy (r = .832) the protein-energy relation is regarded as the more significant biologically. This point of view is based on the fact that energy yield tends to be a simple multiple of protein yield. If there is no elaboration of milk protein there are no lactation energy transformations and there is no milk secretion. On the other hand, elaboration of milk fat may be zero without interrupting milk secretion. The elaboration of milk fat requires the elaboration of milk protein additional to that of fat-free milk secretion. In general, the total (and often enormous) energy transformations of milk secretion depend on and are proportioned to the elaboration of milk protein or nitrogen metabolism of the mammary gland in lactation.

According to the above interpretation it appears futile to try to modify the protein calorie ratio of milk by selective breeding. The protein calorie ratio has a low variability (C.V. = 5) and as between successive lactations of the same cow it shows a low correlation (r = .18). Hence, to increase the proportion of food value (calories) present in the milk as protein, by breeding, would be exceedingly difficult.