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Responses of Dairy Cows to Exogenous Bovine Growth Hormone Administered During Early Lactation¹

Department of Animal Science, Cornell University, Ithaca, NY 14853-4801

⁴ Reprint requests.

ABSTRACT

Bovine growth hormone was administered to eight Holstein cows during two 10-d periods (commencing 20 and 60 d postpartum). Treatments involved daily subcutaneous injection of excipient (control) or of 50 IU growth hormone. Feed intake and yields of milk and milk components were measured during the last 5 d of treatment. In the first injection period, milk yield of treated cows was 6% greater than that of controls (36.2 kg/d). Fat content of milk was increased by treatment with the result that fat yield was elevated by 25%. Protein content was not altered. In the second period, milk yield increased by 12%, but composition of milk was not changed. As a result, milk energy secretion was increased by a similar amount in each treatment period (4.4 versus 4.5 Mcal/d). Feed intake was not changed in either period. During early lactation the ability of cows to increase milk yield in response to exogenous growth hormone may be limited by the supply of glucose for lactose synthesis rather than by ability to mobilize body reserves in support of lactation.

¹ Supported in part by Cornell University Agricultural Experiment Station and The Upjohn Co., American Cyanamid Co., and Monsanto Co. The authors gratefully acknowledge R. F. Olsen, The Upjohn Company, for donation of the bovine growth hormone.

² Department of Dairy and Animal Science, The Pennsylvania State University, University Park, PA.

³ On leave from Department of Animal Science, Massey University, Palmerston North, New Zealand.

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