To understand the ways in which ruminant animals utilise the organic acids which are the products of microbial metabolism of feed carbohydrate.

The underlying thrust of this teaching module has been to emphasise the very distinctive nature of ruminant usage of feed carbohydrate. The consequence of this is that ruminants have very distinctive patterns of intermediary metabolism in liver, muscle, adipose tissue and lactating mammary gland where the products of ruminal metabolism are used for particular purposes.

The organic acids are first taken up from the reticulo-rumen fluid into the cells of the rumen mucosal epithelium. From here they pass into the hepatic portal venous drainage and are substantially taken up by the hepatocytes as the portal circulation flows via the liver sinusoids to the centrilobular venous drainage system. Lactate and propionate are almost wholly removed from the blood during passage through the liver (first pass effect).  In contrast a high proportion of the acetate is not taken up by hepatocytes but passes into the systemic circulation to be utilized by peripheral tissues such as skeletal muscle, adipose tissue, myocardium and the lactating mammary gland. The pattern of butyrate usage is also distinctive; it is extensively metabolised in the cells of the rumen mucosa, at the time of uptake from the rumen fluid, to form ketone bodies, and only a small proportion of butyrate reaches the liver where it is effectively cleared as occurs with lactate and propionate during the first pass through the liver.