A NOTE ON THE EFFECT OF USE OF BOVINE SOMATOTROPIN ON THE FATTY-ACID COMPOSITION OF THE MILK-FAT IN DAIRY-COWS

Commencing on day 100 +/- 10 of lactation, 10 Italian Friesian cows av eraging 32.6 kg milk per day were injected biweekly with recombinant b ovine somatotropin (BST), while 10 other cows averaging 33.4 kg milk p er day were injected with a placebo. Cows were offered ad libitum a to tal mixed diet throughout the lactation. The experiment lasted 16 week s; milk samples were taken before and 16, 62 and 91 days after the com mencement of BST injection. The objective was to determine the impact of biweekly injections of BST on the synthesis and proportion of milk fatty acids, particularly on cis and trans isomers and on fatty acids with an odd number of carbon atoms (C-15 and C-17). A decrease in the proportion of short-chain (C4 to C-14) fatty acids (P < 0.001) and an increase in the proportion of long-chain (C-16 to C20) fatty acids (P < 0.001) were observed in the first period of the treatment. With rega rd to cis and trans isomers, a considerable increase of the cis isomer s (P < 0-001), particularly C18:1cis9 (oleic acid) was observed, while differences in trans isomers were not statistically significant. Conc entrations of C-15 (pentadecanoic acid) were not affected but heptadec anoic acid (C-17) concentration showed a considerable increase (P < 0. 01) but only in the sample taken after 16 days.