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Nutritional Implications of Somatotropin for Lactating Cows¹

Center for Animal Health and Productivity, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348

ABSTRACT

Milk yield, feed intake, physiology, health, and reproduction of cows supplemented with somatotropin are like those of genetically superior cows. Lactation curves are shifted upward and are more persistent Holsteins, Jerseys, Brown Swiss, and Ayrshires respond. In most cases, responses in primiparous and multiparous animals are similar. Milk composition, ration digestibility, maintenance requirements, and the partial efficiency of lactation are not affected by somatotropin. More nutrients are directed to milk synthesis. Initially, body stores of fat, protein, and glycogen provide these nutrients, but after a few weeks, feed intake increases. Cows supplemented with somatotropin should be fed like high producing cows. When ration energy density is increased by feeding grain, buffers such as sodium bicarbonate should be included to prevent alterations of hydrogen balance in the rumen and tissues. Ration energy density can also be increased with ruminally inert fat like calcium salts of fatty acids. Rations should be balanced for rumen degradable and undegradable protein. Rations for high milk yields are expensive, but income over feed costs are greater. Cows should be moved to rations with lower nutrient densities on the basis of body condition and milk yield. Current feeding recommendations can be used for cows supplemented with somatotropin.

¹ Invited paper presented at the 83rd annual meeting of the American Dairy Science Association, University of Alberta, Canada.