Dietary Protein Moderates Acid-Base Responses to Repeated Sprints in Exercising Horses

Restricting dietary protein may reduce endogenous acid load. Horses were fed diets with 10% supplemental corn oil in experiment one and either 0% or 10% supplemental corn oil in experiment two. Also, low protein (7.5% crude protein, LP) fortified with .5% lysine and .3% threonine or high protein (14.5% crude protein, HP) was fed.

Horses underwent similar interval training and standard exercise tests. In experiment two, horses performed an SET prior to conditioning. The SET consisted of warm ups at the walk and trot followed by six repeated sprints and concluding with a 30 minute recovery at the walk. All sprints were at 10 m/s except the SET prior to conditioning in experiment two, which were at 7 m/s. Blood samples were taken every two weeks and as part of SETs. Samples were analyzed for pH, pCO₂, pO2, Na⁺, K⁺, Cl⁻, lactate, total protein (TP), albumin, creatinine and plasma urea-N (PUN). Bicarbonate, strong ion difference (SID) and total weak acids (Atot) were calculated.

Plasma urea-N concentrations were higher in the HP group. Plasma creatinine was not different in experiment one but was higher in the LPHF group in experiment two. Also, the LPHF group had a low body condition score and the same weight therefore had a higher lean body mass. Plasma albumin was not different in either experiment and TP was not different in experiment one. Total protein was higher in the HF groups in experiment two.

Protein moderated acid-base responses to SETs in both experiments. The LP group had higher pH and bicarbonate levels as well as a tendency for a higher SID in experiment one and in the SET prior to conditioning for experiment two. Lower lactate levels were observed in the LP group in experiment one. Following conditioning in experiment two, the LP group had higher pH and bicarbonate levels but only combined with HF.

Restricting dietary protein can increase pH and bicarbonate levels and high fat has been shown to improve fatty acid oxidation and spare muscle glycogen. Therefore, restricting dietary protein especially in combination with high fat may be beneficial for the exercising horse.