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The Effects of Hourly Milking with the Aid of Intravenous Injections of Oxytocin¹

Dairy Husbandry Department, University of Minnesota

ABSTRACT

Milking hourly with oxytocin brought about increases in the rates of secretion of several milk constituents, particularly during the latter part of the trials. The fat secretion rate was particularly high after an early period of low secretion. It would appear that several milk constituents are independently formed in, or transported to, the lumen of the alveoli as seen in the independent hourly variation of total milk, milk fat (content and composition), the members in the nitrogen partition fraction, and lactose. Although most of these fractions fluctuated closely about a mean value, others fluctuated more widely and, therefore, did not closely approach the mean value in a 12-hour sample because of hourly random variability. Only total milk yields and butterfat content formed a definite time-production pattern related to the experimental routine, and these patterns were considerably different from one another. When the intervals between milkings were increased step-wise up to 16 hours, fat secretion was considerably above the rate seen in hourly milkings. Total milk secretion rate was not changed from the hourly rate until the intervals reached 16 hours, when the rate was still above the pre-experimental rate.

¹ Paper No. 3057, Scientific Journal Series, Minnesota Agricultural Experiment Station.

² Present address: Dairy Department, University of Georgia, Athens.