HORMONAL PROFILES, RUMEN VOLATILE FATTY-ACIDS AND MILK TRANS-C18 1 FATTY-ACIDS IN RELATION TO MILK-FAT CONTENT IN RESTRICTED OR AD-LIBITUM FED DAIRY-COWS/

Plasma levels of insulin, somatostatin, gastrin and oxytocin, rumen vo latile fatty acid (VFA composition and content of trans-C 18:1 fatty a cids in milk fat were studied in relation to milk fat content in 12 da iry cows, Half of the cows were fed restrictedly according to Swedish standards (R) and half were Fed ad libitum GAL). In the previous lacta tion three cows from each treatment had a high milk fat content (HF) a nd three bad a low fat content (LF). Blood and rumen samples were take n in lactation weeks (1w) 8 and 21. In Inr 21, the AL cows had a lower proportion of acetate in the rumen VFA, a higher plasma level of gast rin and a different diurnal pattern of insulin compared with the R cow s, The LF cows had a higher plasma level of insulin after feeding than the I-IF cows in 1w 21. Correlation analysis showed that the plasma l evel of somatostatin was positively related to milk fat content both i n 1w 8 and in 1w 21. In addition, the milk trans-C18:1 fatty acids wer e inversely related to milk fat content in Iw 8, whereas the proportio n of butyrate in rumen VFA was positively related and the proportion o f propionate was inversely related to milk fat content in Iw 21. A rou te by which somatostatin could regulate milk fat synthesis is discusse d.