Milk lipoprotein lipase activity during long-term administration of recombinant bovine somatotropin

The effect of long-term administration of recombinant bovine somatotropin to dairy cows on milk lipoprotein lipase activity was investigated. Recombinant bovine somatotropin was administered daily to 32 cows (8/treatment). Treatments were 0 (control), 12.5, 25.0, and 50.0 mg/d or recombinant bovine somatotropin administered in once daily intramuscular injections. Treatments began at 28 to 35 d of lactation and continued until 294 d of lactation. Recombinant bovine somatotropin treatments had no significant effect on milk lipoprotein lipase activity; enzyme activity for each treatment was 97.87, 108.96, 99.96, and 92.43 units/ml of milk, respectively. A significant effect of the stage of lactation was unrelated to recombinant bovine somatotropin administration. Enzyme activity peaked at approximately 20 wk of the treatment or 25 wk postpartum. These results indicate that long-term administration of recombinant bovine somatotropin does not alter the processes that lead to lipoprotein lipase activity in milk.