EFFECT OF DIETARY CATION-ANION BALANCE ON MINERAL BALANCE IN ANAEROBICALLY EXERCISED AND SEDENTARY HORSES

Eight geldings and four mares were randomly assigned treatments within three 4x4 Latin square design experiments to study the effects of die tary cation-anion balance (DCAB) on mineral balance and dry matter dig estibility in sedentary and anaerobically exercised horses. Four diets with an average DCAB (calculated as meq ((Na+K+) - Cl-)/kg of diet dr y matter) of +24 (Low, L), +127 (Medium Low, ML), +227 (Medium High, M H) and +352 (High, H) were fed for a 21 day adjustment period followed by a 72 hour collection period. Diets consisted of a pelleted base co ncentrate of corn, soybean meal and cottonseed hulls fed with either n ative prairie grass or bermuda grass hay in a 60:40 ratio. Diet L was formed by adding calcium chloride and ammonium chloride to the base co ncentrate, diet ML was formed by adding calcium chloride, and diet H w as formed by adding potassium citrate and sodium bicarbonate. Diet MH received no supplementation and served as the control. Representative samples of feed, feces and urine were analyzed for mineral content and mineral balances were calculated by difference. Fecal output was grea ter (p <.05), and thus, dry matter digestibility was lower in exercise d horses consuming diet L versus diet H. Sodium balance was greater (p <.05) in sedentary horses consuming diet MH as compared to those cons uming diets ML and L Sodium balance was greater (p <.05) in exercised horses consuming diet H as compared to those consuming diets ML and L. Potassium balance was greater (p <.05) in sedentary horses consuming diet H as compared to those horses consuming diet ML, however, potassi um balance was not affected by DCAB in exercised horses. No significan t differences were detected in chloride or magnesium balances in the s edentary horses, although chloride balance was greater (p <.05) and ma gnesium balance was lower (p <.05) in exercised horses consuming diet L as compared to all other diets. In sedentary horses, phosphorus bala nce was reflective of intake with differences (p <.05) observed betwee n all treatments. However, in exercised horses, phosphorus balance was lower (p <.05) only for those consuming diet L. Calcium balance decre ased significantly as DCAB decreased between all treatments in sedenta ry horses, while calcium balance in exercised horses was greater (p <. 05) for horses consuming diet H as compared to those consuming diet L. Previous research from our laboratory has shown that both exercised a nd sedentary horses consuming diets with a low DCAB experience a nutri tionally induced metabolic acidosis. The current data indicate that an aerobically exercised and sedentary horses consuming these diets excre te significantly more calcium in the urine resulting in decreased calc ium balances. Prolonged consumption of diets with a low DCAB may lead to a significant demineralization of bone and a subsequent weakening o f the skeleton.