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-Lactalbumin, Fatty Acids, and Mineral Elements1,2,Department of Animal Science, Cornell University, Ithaca, NY 14853
US Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705
Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061
US Department of Agriculture, Agricultural Research Service, Ithaca, NY 14853
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ABSTRACT
Tissue-specific effects of bovine growth hormone on lactating dairy cows were examined by analysis of milk composition. Milk samples were from 6 cows that received subcutaneous injections of 0, 5, 10, 25, 50, and 100 IU/d of growth hormone in a Latin-square design. Samples from the last 5 d of each 10-d treatment period were pooled for analyses of milk components. Concentration of 
-lactalbumin in milk increased progressively across the treatment range up to 32% above controls (1.30 mg/nl) at the 100 IU dose. Specific -lactalbumin synthesis (expressed as a percent of total milk protein) was also increased. Secretion of de novo synthesized fatty acids (short and medium chain length) in milk was increased, but response plateaued between the 50 and 100 IU/d. Secretion of preformed (long-chain) fatty acids progressively increased across the entire dose range. Thus, the percentage of long-chain fatty acids in milk increased at the highest doses of hormone. Changes in fatty acid composition of milk were apparently related to energy status; the milk response to 50 and 100 IU/d of growth hormone caused cows to be in or near negative energy balance. Exogenous growth hormone did not affect the concentration of calcium, phosphorus, sodium, iron, copper, and manganese in milk. Results are consistent with growth hormone functioning in homeorhesis to coordinate the partitioning of all nutrients to support the increased secretion of milk and milk components.
1 Supported in part by Cornell University Agricultural Experiment Station, American Cyanamid Co., The Upjohn Co., and Monsanto Industrial Chemicals Co.
2 Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the US Department of Agricutlure and does not imply its approval to the exclusion of other products that may also be suitable.
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