Rumen fermentation and splanchnic metabolism affect the relationship between the chemical composition of the feed and the nutrients available to the mammary gland and other peripheral tissues in the dairy cow. Conventional feed evaluation systems don’t allow the nutritionist to design diets based on the demand for specific nutrients, but primarily base predicted animal responses on the energy content of digested organic matter. In a nutrient based feed evaluation system (NBFE) the chemical composition of the feed and monitoring of ruminal variables in real time can be used as input to simulation models describing fermentation and intermediary metabolism. The aim of the system is to analyse/evaluate dietary adjustments according to specific metabolic needs of the dairy cows under specified physiological conditions. It’s mandatory that NBFE systems account for all major nutrient fractions absorbed and metabolised in the dairy cow. Short-chain fatty acids (SCFA) have been particularly troublesome in this respect because it generally has been assumed that a large proportion of ruminally absorbed SCFA is metabolised by the rumen epithelium and therefore is not available to the liver or peripheral tissues. The aim of this presentation is to review the interrelations between ruminal production, portal absorption, and peripheral availability of SCFA in the ruminant and to discuss how the metabolism of SCFA might be incorporated into future NBFE systems.