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A Comparison of Guernsey Sires

III. Based Upon the Average Persistency of Fat Secretion during the Lactation of the Daughters

Department of Dairy Husbandry, University of Missouri, Columbia, Missouri

ABSTRACT

During the past few years, a number of studies have been made of the changes in the rate of secretion of milk and fat during the lactation. It has been found that many factors which may be considered environmental or physiological, influence the shape of the curves of secretion. These factors include season, nutrition, pregnancy, age and frequency of milking. There are undoubtedly many others which fall into this class.

Another important cause of variation in the shape of the lactation curve is due to the inheritance of the animal. Exactly what part of a cow's milk and fat production is due to environmental factors and what part due to inheritance is difficult to determine. The view is held that faulty nutrition and management may lower production but that it is impossible to increase production above the limit set by inheritance (1).

As yearly or lactational milk yield is a very complicated process, it was thought that a step in the analysis of the complicated mechanism of the inheritance of milk and fat secretion might be made by separating the principal parts of the curve of lactational milk secretion and by studying each part separately.