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Studies in Milk Secretion

XI. Relation between the Butterfat percentage of one lactation and the Butterfat percentage of a Subsequent Lactation in Guernsey Advanced Registry Cattle¹

Maine Experiment Station, Orono, Maine

ABSTRACT

This paper presents data to show the reliability of an advanced registry record of Guernsey cattle in predicting what the cow's butterfat percentage will be in a subsequent advanced registry retest for other lactations. The principle facts resulting from this study may be briefly stated as follows.

Unlike milk yield, the butterfat percentage of these Guernsey advanced registry cows shows no increase on retest. It remains approximately the same in the retest as in the first test.

The variation of the butterfat percentage is closely similar to that of other breeds of cattle.

The relation of the butterfat percentage of one lactation to that of another is high, ranging from 0.637 to 0.893 in terms of the correlation scale. The average correlation coefficient is 0.792. This average is 1 1/10 times as high as that for milk yield of these same cows, or a butterfat percentage record may be more accurately predicted from a previous test than can a record for milk yield be predicted from a previous test. Comparison of these results with records of a pure-bred Jersey herd for the relation of one lactation to another indicates that the advanced registry records predict a subsequent advanced registry performance more accurately than would be expected to be the case for all Guernsey cows.

A comparison of the value of a month's egg record in predicting the other eleven months' record with Guernsey butterfat percentage records shows that a Guernsey butterfat percentage record predicts more accurately the subsequent butterfat percentage record than does an egg record predict the subsequent performance of the hen.

Comparison of scoring as a method of selecting cattle for milk yield or butterfat percentage with an advanced registry record for selecting milch cows shows the advanced registry record to be several times more valuable than the score card.

Equations are presented to determine from one lactation's advanced registry butterfat percentage record what the probable butterfat percentage record at a subsequent lactation will be.

¹ Paper from the Biological Laboratory of the Maine Agriculture Experiment Station, No. 145. This paper is one of a series of investigations in animal husbandry the continued prosecution of which has been made possible by a grant to the author from The Rockefeller Institute for Medical Research.