Effect of Diet on Serum Electrolytes, Blood pH and Markers of Bone Remodeling in Horses
High dietary acid load (DAL) has been associated with metabolic acidosis in many species. Racehorses are typically fed grain-rich diets, which represent high DAL that may decrease blood pH to result in calcium mobilization from bone as a buffer. In young racehorses under the pressures of growth and bone remodeling due to high impact exercise, high DAL may hinder normal bone development and predispose these athletes to injury. This paper describes two studies investigating a possible association between grain consumption and acidosis, alterations in serum electrolytes, and bone remodeling in horses.
Study 1: Thirty-nine racehorses and 11 pastured horses were used in a pilot study. Data was collected at a single time point and included grain intake (kg), work status, age, gender, breed, blood pH, iCa, HCO3, TCO2, BE, BEecf, K, Cl, PTH and Osteocalcin (OC). Grain intake was not significantly associated with lower pH, but lower mean pH and increased HCO3 and TCO2 were observed with grain consumption. Significant differences between working and sedentary horses were seen in iCa, BE, BEecf, TCO2 and HCO3. Together with the observed increase in blood pH after exercise, this suggested grain-induced acidosis may be offset by exercise-induced alkalosis. A tendency for higher grain intake to result in increased OC was also noted. This suggested increased bone turnover may be associated with grain consumption.
Study 2: Ten sedentary horses were used in this 24 hour study, 5 fed grass hay only and 5 fed grain and grass hay. Data collected included hourly measurements of blood pH, iCa, HCO3, TCO2, BE, SID, K, Cl, Na, glucose and OC. Mean pH in the grain group relative to the control group was significantly lower after eating, but was significantly higher at later collections. Grain consumption was significantly associated with lower HCO3, TCO2, and BE. SID was significantly lower in the grain group near the time of decreased buffer and pH, supporting DAL as causal.
These data support that high DAL significantly affects blood pH and acid-base balance; however, no evidence of increased bone turnover was seen, as demonstrated by lack of significant increase in iCa and OC. Further research using a more sensitive indicator of bone turnover and/or a longer time frame and/or exercising horses may help determine if high DAL plays a role in bone turnover in the horse.