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Factors Influencing the Amount of Milk "Let-Down" Hormone in the Posterior Lobe of Jersey Cattle¹

Ruakura Animal Research Station, Hamilton, New Zealand, and the Missouri Agricultural Experiment Station, Columbia

ABSTRACT

The milk let-down hormone content of the posterior pituitary glands of dairy-cattle has been estimated. The cattle ranged in ages from 1 mo. to 5 yr. Eighteen calves between the ages of 1 and 5 mo., two 15-mo. old heifers and five cows ranging from 2 to 5 yr. were included in the study. The weight of the dried, defatted posterior lobe, its total milk let-down activity, activity per unit weight of dried gland and the activity per unit of body weight were determined. The total milk let-down activity rises with age in calves, while the mature cows show a decline. The activity per unit of body weight rises in calves until at about 3 mo. the figure reaches a fairly steady level. Mature cows show a much lower relative level. The weight of dried defatted posterior lobe shows no trends with increasing age in calves but appears to fall in mature cows.

¹ Contribution from the Department of Dairy Husbandry, Missouri Agricultural Experiment Station, Journal Series no. 1306.

² Fulbright Research Scholar.