NEFA, BHBa, UREA and Liver Enzyme Variation in the Bloodstream of Weaned Foals up to 18 Months of Age

SIMPLE SUMMARY: Energy balance assessment of the growing horse requires a complex nutritional evaluation. Some biochemical parameters can be of clinical importance to prevent the onset of metabolic disorders. The adequate nourishment of body tissues in the growing foal may represent an issue in the practice, given the dynamic change of body composition, in view of the potential mobilization of fat from tissue depots and increasing lean mass. As such, the maintenance of adequate body weight and body measures over time (optimal growth curve accomplishment) and the fulfillment of nutrient requirements are cornerstones of individual feeding plans for the expression of the athletic potential of the future sport horse. In this scenario, the metabolic evaluation of growing foals turned out to be a valuable tool to consider the energy distribution within the animal body. In view of those particular conditions, non-esterified fatty acids (NEFA), beta-hydroxybutyric acid (BHBa), UREA and liver enzymes showed to serve as indicators to monitor energy balance and health in growing foals from weaning to 18 months of age. ABSTRACT: The pattern of selected metabolites for interpreting homeostasis during the growth of foals can be used as an indicator of energy balance state and liver health. Against this background, the literature on circulating parameters of foals across growth stages is scanty. We hypothesized that circulating metabolites indicating energy distribution such as non-esterified fatty acids (NEFA), β-hydroxy-butyric acid (BHBa), UREA and liver enzyme-like γ-glutamyl-transferase (γ-GT) [interpreted in the light of circulating total bilirubin (TBIL), alanine aminotransferase (ALT) and aspartate aminotransferase (AST)] may be used to monitor the energy balance of growing foals. A total of 12 Anglo-Arab (AA) foals from the same stable were enrolled in this trial. All foals were serially weighed on a digital scale and sampled for total blood at weaning, at 12 and 18 months of age. Feeding and keeping conditions were similar for all the foals involved. Animals appeared healthy and no signs of poor growth performance were pointed out. The peak of circulating NEFA mobilized from body depots was reached at one year of age but markedly dropped at 18 months, when BHBa increased (p < 0.001) alongside with liver enzyme. BHBa and γ-GT levels turned out to positively correlate (p = 0.051). However, at 6, 12 and 18 months, γ-GT dropped in the physiological reference range for the horse, thus showing no prognostic value. ALT and UREA significantly increased (p = 0.008 and p = 0.006, respectively) when NEFA also increased (p = 0.001). Liver enzyme increase could be associated with fat mobilization and ketone bodies production meanwhile amino acid transamination for energy purposes led to the increase of UREA in the bloodstream. However, no prognostic value to liver enzyme could be attributed in this trial.