EFFECTS OF RECOMBINANT BOVINE SOMATOTROPIN ON FATTY-ACID COMPOSITION OF MILK FROM COWS IN LATE LACTATION

To investigate the effects on milk fatty acid composition of recombina nt bovine somatotropin (rBST) administered under South African conditi ons, 26 dairy cows were paired into two groups 84-112 days after calvi ng. At two-weekly intervals the cows in the experimental group were in jected with 500 mg of rBST in a slow-release formulation, while cows i n the control group were injected with the excipient. Milk specimens t aken at two-weekly intervals from 36-40 weeks post partum until drying off were analysed for fatty acid composition. The cows given rBST pro duced milk, with less short-chain (C4), more medium-chain (C-8-C-16) a nd less long-chain (C18) acids. Hexanoic acid content was unaffected. rBST administration did not affect the proportion of unsaturated fats in the milk. Differences in milk composition between cows and through time were larger than those due to rBST administration. Treated and co ntrol cows showed synchronized fluctuations in milk fatty acid composi tion that were larger than the differences due to rBST.