Developmental Changes During the First Year of Life in Plasma Tryptophan Concentration of the Foal

Circulating tryptophan (TRP) levels can influence protein synthesis in various tissues during early stages of life. It is important to investigate factors that influence TRP dynamics to evaluate results of TRP use in equines. Previous studies have demonstrated that plasma TRP levels in the first periods of life are indicative of brain serotonin synthesis and that in horses there may be breed differences in the behavioral response to TRP administration. Current research has investigated the pattern of plasma TRP concentration in growing foals of two different breeds: Anglo-Arabian (AA) and Sicilian Oriental Purebred (PSO). Blood samples were collected from 10 clinically healthy colts, ages 1 to 12 months old. Plasma TRP concentrations were determined by high-performance liquid chromatography. Two-way analysis of variance showed age- and breed-related differences. A positive significant correlation was found between age and TRP concentration (r = 0.6, P < .001). After weaning (7th month of age) TRP levels were significantly higher than in previous months. PSO colt foals had TRP levels significantly higher than AA colt foals in the 1st, 2nd, and 12th months of life. These findings suggest that plasma TRP dynamics in growing horses are influenced by age and breed and should be taken into consideration for TRP experiments in equines.