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

Abstract

Plasma levels of insulin, somatostatin, gastrin and oxytocin, rumen volatile fatty acid (VFA) composition and content of trans‐C18:1 fatty acids in milk fat were studied in relation to milk fat content in 12 dairy cows. Half of the cows were fed restrictedly according to Swedish standards (R) and half were fed ad libitum (AL). In the previous lactation three cows from each treatment had a high milk fat content (HF) and three had a low fat content (LF). Blood and rumen samples were taken in lactation weeks (lw) 8 and 21. In lw 21, the AL cows had a lower proportion of acetate in the rumen VFA, a higher plasma level of gastrin and a different diurnal pattern of insulin compared with the R cows. The LF cows had a higher plasma level of insulin after feeding than the HF cows in lw 21. Correlation analysis showed that the plasma level of somatostatin was positively related to milk fat content both in lw 8 and in lw 21. In addition, the milk trans‐C18:1 fatty acids were inversely related to milk fat content in lw 8, whereas the proportion of butyrate in rumen VFA was positively related and the proportion of propionate was inversely related to milk fat content in lw 21. A route by which somatostatin could regulate milk fat synthesis is discussed.