Dietary protein influences acid-base balance in sedentary horses

Abstract

Summary The objective of this study was to evaluate acid-base balance of sedentary horses fed 2 levels of dietary protein to determine if protein intake influences acid-base balance. Ten horses of Thoroughbred type were randomly assigned to 2 daily rations with different overall protein concentrations (7.5% low protein [LP] and 12% high protein [HP]). Their rations consisted of 3 meals of a LP or HP concentrate along with grass hay (timothy/orchard grass). Horses were fed to maintain body weight and condition. They were housed in box stalls during the day and turned out in a dry lot at night over an 8-week period. Body weights, body condition score, and venous blood samples were taken every 2 weeks. Plasma was analyzed for total protein, albumin, creatinine, urea-N, pH, lactate, potassium (K+), sodium (Na+), chloride (Cl−), and partial pressure of carbon dioxide (pCO2). Bicarbonate, strong ion difference (SID), and total weak acids (Atot) were calculated. Diets did not have differences in dietary cation-anion difference (DCAD); however, protein intake was different. Horses fed the LP diet had lower urea-N (P = .001), higher blood pH (P = .037), and higher HCO3− (P = .011) compared with the HP group. The LP group had higher SID at the last sampling period (P = .029) and higher K+ at day 42 (P = 0.011). No difference was found for body weight or body condition score. No differences due to diet were found for plasma total protein, albumin, creatinine, lactate, Na+, Cl−, pCO2, and Atot. The difference in pH appeared dependent on SID, with no effect of pCO2 or Atot on pH; however, this may not completely explain the lower pH in the HP group. Since there was no difference in DCAD between the diets, the effect on acid base may be due to dietary protein intake. Excess intake of protein results in oxidation of amino acids and an overall amino acid imbalance that contributes to the acid load and lowering of blood pH as observed in this study.