Influence of Feeding and Fasting on Plasma Free Amino Acids in the Equine

The influence of feeding and fasting on plasma free amino acid (PFAA) concentrations was evaluated using six mature geldings. Blood samples were obtained at feeding time (0 hr.) and at 2-hr. post feeding intervals through 12 hr. post feeding and at 6-hr. intervals throughout a 48-hr. fast. Analysis of PFAA indicated no significant diurnal variation nor difference between days. PFAA increased upon feeding; essential amino acids peaking at 132% of basal 2-hr. post feeding with a relatively rapid return to basal levels while nonessential amino acids tended to rise to a lower plateau of about 120% of basal but remained at an elevated level through 8 hr. post feeding. Both essential and nonessential amino acids tended to fall to near a basal level at 18 to 30 hr. of fast with a succeeding rise in most essential amino acids to 130% of basal at 48 hr. of fast. Nonessential amino acids exhibited much less of a fasting rise to 121% of basal at 48 hr. of fast with the exception of alanine and glycine which rose to 154% and 133% of basal, respectively, at 48 hr. of fast.