Relationship of Plasma Free Fatty Acids to Other Blood Components in Ruminants under Various Physiological Conditions1,2,3,4

Abstract

Experiments were conducted with cows and goats to determine the normal concentrations of plasma free fatty acids (FFA) and their relationship to blood sugars and blood ketones. Plasma FFA concentrations in cows and goats were within the ranges reported for nonruminant species (100–2,000 μeq/liter), but under normal non-fasting conditions were lower (200–300 μeq/liter) than values reported for nonruminants. The plasma FFA concentration tended to be depressed 4 to 6 hr after feeding, at which time blood sugars were also depressed and blood ketones increased. Upon fasting, the plasma FFA concentration increased, whereas the blood sugars were depressed and blood ketones increased. The response of all blood components to feeding or fasting was much greater in milking than in dry animals. Correlations under fed and fasting conditions, respectively, were sugar vs. ketones, −.54, −.63; sugar vs. FFA, .01. −.75; ketones vs. FFA, .10, .81. This suggests that blood sugar is a controlling factor in ketogenesis, under both fed and fasting conditions, but that plasma FFA are a primary source of ketones only under fasting conditions. The plasma FFA concentration was elevated at parturition, but was not consistently higher at the time of peak milk production.