Effect of treating dairy cows of three breeds with recombinantly derived bovine somatotropin for three years

Abstract

Jersey, Friesian (Fr) and Dutch Red and White (DRW) dairy cows were treated over three lactations with BST, recombinantly derived bovine somatotropin (somidobove), in a sustained-delivery vehicle injected subcutaneously once every 28 days. In the first data set (indoor+pasture trials: 243 lactations from 126 cows) the response to BST treatment in milk energy production was similar for the breeds: Jersey 7.4, Fr 8.5 and DRW 8.9 MJ day -1, respectively, was slightly higher in cows than in heifers: 9.5 and 7.1 MJ day -1, respectively; and was higher on concentrates than on roughage-based diets: 10.6 and 6.0 MJ day -1, respectively. Control cows gained more body weight (5–17 kg) in the treatment period than treated cows. Using the second data set (indoor trials: 163 lactations from 93 cows) the response to BST treatment during the treatment period of 168 days was 9, 1 and -2 MJ net energy (NE) day -1 for energy intake, 14.0, 12.2 and 10.6 MJ day -1 for milk energy production, and 7, -11 and -9 kg for body weight during the first, second and third successive lactations respectively. In this period, plasma 3-hydroxybutyrate levels were higher in treated than in control cows: 204, 188 and 266 μmol l -1 in the three successive lactations, respectively, as were plasma free fatty acid (NEFA) levels at 13, 76 and 72 μmol l -1, respectively. This indicated a higher body fat mobilization in treated cows, especially in the second and the third successive lactations. Somatic cell count in milk from treated cows was respectively 136, 54 and 25 × 10 3 cells ml -1 higher than in milk from control cows for lactations 1, 2 and 3. The repeatabilities of the maximum response to BST treatment for milk energy production between periods within lactations and between lactations were low: 0.25 and 0.57 respectively. Calves from treated cows had a 5% lower birth weight than calves from control cows. Over a 3-year period no differences in fertility traits, disease frequency and reasons for culling were found between control and treated cows.