Dietary protein and fat effects on protein status in Arabian horses during interval training and repeated sprints

This study tested the hypothesis that decreasing dietary protein quantity while increasing protein quality may reduce the undesired effects of excess protein without risking protein deficiency in exercising horses. Twelve horses were assigned to a 2 × 2 factorial experiment: 2 fat levels, 3% low-fat (LF) or 13% high-fat (HF), and 2 protein levels, 7.5% low-protein (LP) or 14.5% high-protein (HP) crude protein (CP). Horses were fed the diets for a 4-week period, then underwent a standardized exercise test (SET). Horses were then trained for 11 weeks, and then underwent another SET. Blood samples were taken every 2 weeks and during SETs. Plasma concentrations of albumin, total protein, urea nitrogen, and creatinine were determined.

The plasma urea nitrogen concentration was higher for horses in HP groups during the experiment, as well as during SET-1. An interaction existed for plasma urea nitrogen during SET-2 but was higher for HP only in combination with HF. During SET-2, higher total protein was associated with HP. An interaction developed during SET-2 for creatinine but was higher for LP only in combination with HF.

These observations indicated no detrimental effect of LP on protein status and suggest that improving protein quality by limiting amino acids while limiting protein quantity in combination with fat may improve the amino acid profile of the diet, contributing to improved protein utilization, which may aid in supporting muscle mass and minimizing excesses of amino acids.