The effect of treatment of dairy cows of different breeds with recombinantly derived bovine somatotropin in a sustained-delivery vehicle

Abstract

After calving 16 Friesian, 16 Jersey and 16 Dutch Red and White cows were taken into a 252-day experiment to determine the response in milk production, body weight and feed intake to the administration of somidobove (recombinantly derived bovine somatotropin) in a sustained-delivery vehicle. The experiment was divided into an 84 days preliminary period and six consecutive 28-day treatment periods. Four treatments were used: an untreated control and 3 different levels of somatotropin, 320, 640 and 960 mg in a sustained-delivery vehicle, administered once every 28 days by subcutaneous injection. Animals were housed and individually fed ad libitum a complete diet of 50% concentrates and 50% roughage. For none of the analysed characteristics a significant breed × treatment interaction was detected. The 640-mg dosage gave optimum results: in the treatment period the calculated milk energy output increased on an average 19% in Dutch Red and White, Jersey and Friesian cows by an increase in milk yield (3.3 kg) and fat percentage (0.24%). Treatment with somatotropin did not affect protein and lactose percentage, somatic cell count, calcium, magnesium and phosphorus levels in milk. Nonesterified fatty acids (NEFA) in milk of treated cows tended to be lower than in control cows. Glucose, insulin and thyroxin levels in plasma were not affected by somatotropin treatment. The plasma levels of NEFA tended to be higher after the first 3 injections, and that of 3-hydroxybutyrate after the first injection with the higher and medium dosages. The level of urea tended to be lower in treated cows; somatotropin was significantly higher in treated cows. The fluctuations in milk yield and milk composition over a 28-day period indicate that the release characteristics of the release system should be improved to get a more natural lactation curve for treated animals.