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Effect of Exogenous Bovine Somatotropin on Pubertal Mammary Development in Heifers¹

National Institute of Animal Science, Research Centre Foulum, DK-8833 Orum Sonderlyng, Denmark

R. Michael Akers

Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061

Dale E. Bauman²

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

² Reprint requests.

ABSTRACT

Nine pairs of identical twins were used to examine the effect of exogenous bovine somatotropin on mammary growth and development in dairy heifers. One twin received a daily subcutaneous injection of somatotropin (20 IU) and the other received excipient. Treatments commenced at 8.0 mo of age (179 kg live weight) and continued for 15.6 wk, at which time heifers were slaughtered and mammary development evaluated. Treatment with somatotropin resulted in an increase in mammary parenchyma and a decrease in extraparenchymal tissue and weight of mammary glands. Increases in parenchyma were 46% as determined by computer assisted x-ray tomography and 18% as determined by dissection. Differences between the two techniques related to the ability of computer assisted x-ray tomography technique to exclude fat deposits and connective tissue fromparenchymal estimates. Chemical composition (39% water, 7% protein, and 54% fat) as well as histological and cytological appearance of the mammary parenchyma were not affected by the treatment. Therefore, treatment with exogenous somatotropin around puberty enhances the growth rate of mammary parenchymal tissue. Additional studies are required to examine whether this enhanced mammary development will increase milk yield during subsequent lactations.

¹ Supported in part by Bergsoe Foundation, Cornell University Agricultural Experiment Station, Danish National Agricultural and Veterinary Research Council, Danish National Institute of Animal Science, Virginia Polytechnic Institute and State University Agricultural Experiment Station, and The Upjohn Company. Preliminary data in this study were presented at the 34th Annual Meeting of European Assoc. Animal Production, October 3 to 6, 1983, Madrid, Spain.

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