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A Study of the Influence of Thyroxin on Milk Secretion^*

Department of Dairy Husbandry, The Pennsylvania State College, State College, Penn.

ABSTRACT

Two purebred Brown Swiss cows were injected intravenously with thyroxin alternately over three 28 day periods at a rate calculated to increase the basal metabolic rate by 10 per cent.

The quantity of milk secreted was weighed and analyses of the milk were made to determine the specific gravity, the weight of milk fat produced, and the percentages of milk fat, lactose, protein, solids-not-fat, lactalbumin, and lactoglobulin. Body weights were taken each 28 days.

Two purebred Holstein-Friesian cows were given intravenous injections of thyroxin at seven day intervals for three weeks at a rate calculated to increase the basal metabolic rate by 30 per cent. Careful observations were made on the quantity of milk secreted by these cows.

An increase in milk secretion resulted from 25 mgm. thyroxin injections. They were most effective during the period of declining lactation just previous to the last few weeks of the lactation period. They were less effective at the peak of production and at the extreme latter end of the lactation period the effect was hardly significant.

The composition of the milk as shown by the constituents for which analyses were made was not significantly altered.

^* Publication authorized by the Director of The Pennsylvania Agricultural Experiment Station, November 5, 1934, as Technical Paper No. 662.