Effect of recombinant bovine somatotropin and calcium soaps on milk yield and composition.

The effects of recombinant bovine somatotropin (GH) treatment and added dietary calcium soaps on milk yield and composition (protein and fat percentages, somatic cell counts, fatty acid composition and nitrogen distribution) of lactating dairy cows were investigated. 80 dairy cows averaging 119.128.9 days in milk, were divided into 4 groups: (1) group C (control diet); (2) group SAP (0.5 kg/day added dietary calcium soaps); (3) group GH (control diet + GH); (4) group SAP + GH (0.5 kg/day added dietary calcium soaps + GH). GH, in a prolonged-release vehicle (640 mg), was injected at 28-day intervals for 84 days (3 treatment cycles). Animals were given a total mixed ration. Milk yield was increased by GH treatment (C: 28.78, SAP: 28.79, GH: 30.27, SAP + GH: 30.63 kg/day; P<0.01), whereas it was not affected by calcium soap addition. Milk fat and protein percentage were not affected by treatments. Seven days post-injection, GH lowered milk urea content (C:6.79, SAP:7.09, GH:6.17, SAP + GH:5.81 mmol/l; P<0.05) and increased the proportion of long-chain fatty acids in milk fat (C:33.71, SAP:34.55, GH:35.56, SAP + GH: 37.74%; P<0.05). No significant effects on milk casein content were found.