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Effect of Repeated Injection of Estrogen on Milk Yield of Nulliparous Heifers^{1, 2,}

Department of Dairy Husbandry, University of Missouri, Columbia

ABSTRACT

Twelve dairy heifers of several breeds and varying in age from seven months to three years were stimulated to secrete milk by the daily injection of estradiol benzoate (E.B.) for 2 wk at a level of 0.3 mg/100 lb body weight. Hand and machine milking was initiated twice daily and continued for 6 wk. Maximum daily milk yield based on a weekly average was used as an index of the extent of mammary glandular tissue. Although little milk was secreted by the calves, the heifers of increasing age secreted considerable milk. These data further confirm the suggestion that lobular-alveolar growth is stimulated by the secretion of ovarian hormones during recurring estrous cycles.

The ten older heifers were again administered E.B. at the same level for 1 wk starting the 7th wk. At the beginning of the second course of injections, the mean maximum milk yield was 12.7 lb/day, whereas, following restimulation, their mean maximum production increased to 24.5 lb/day, an increase of 92.9%. Four heifers given a third course of injections of E.B. after 15 wk of experimental lactation were stimulated to secrete 22.4% more milk.

¹ Contribution from the Missouri Agricultural Experiment Station Journal Series No. 2788. Approved by the Director.

² Aided in part by a grant from the U. S. Atomic Energy Commission [Contract No. AT (11-1)-301-101]. Syntex Lab. Inc., Palo Alto, California, has generously contributed ovarian hormones.