Effect of dietary cation-anion difference on mineral balance, serum osteocalcin concentration and growth in weanling horses

Abstract

Summary Sixteen Quarter Horse weanlings were used in a splitplot design experiment to determine the effects of dietary cation-anion difference (DCAD) on mineral metabolism, osteocalcin concentration and variables of growth. Horses were blocked by age and sex and then randomly allotted to two treatment groups (High or Low). Experimental diets with a DCAD of +325 (High, H) and −52 (Low, L) were formed by supplementing diet H with sodium bicarbonate and diet L with calcium chloride. The DCAD was calculated as meq (Na+K)−(Cl+S)/kg of diet DM. The 25-week trial consisted of three 72 h collection periods at 150, 240 and 330 d of age during which a complete urine collection was taken. Multiple fecal grab samples were collected to represent every 2 h post-feeding during each collection period. Venous blood samples were taken for analysis of serum osteocalcin concentration. Weekly measurements were taken to monitor skeletal growth. Representative samples of feed, feces and urine were analyzed for mineral content and apparent mineral balances were calculated by difference. Although osteocalcin concentration did not differ significantly between diets H and L at 150 and 330 d of age, it was higher (P .05) was detected between treatments in any skeletal growth variable measured. Phosphorus balance and digestibility did not differ significantly between treatments across d of age. However, digestibility of P was lower (P .05) in Ca digestibility across d of age. These findings suggest that horses consuming a low DCAD diet are able to compensate for the increased urinary excretion of Ca by enhancing intestinal Ca absorption and thereby increasing daily CA balance and digestibility.