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

Sixteen Quarter Horse weanlings were used in a split-plot design experiment to determine the effects of dietary cation-anion difference (DCAD) on mine ral metabolism, osteocalcin concentration and variables of growth. Horses w ere blocked by age and sex and then randomly allotted to two treatment grou ps (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 di et L with calcium chloride. The DCAD was calculated as meg (Na + K) - (Cl S)/ kg of diet DM. The 25-week trial consisted of three 72 h collection pe riods 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-feed ing during each collection period. Venous blood sample!; were taken for ana lysis of serum osteocalcin concentration. Weekly measurements were taken to monitor skeletal growth. Representative samples of feed, feces and urine w ere analyzed for mineral content and apparent mineral balances were calcula ted by difference. Although osteocalcin concentration did not differ signif icantly between diets H and L at 150 and 330 d of age, it was higher (P<.05 ) at d 240 in horses consuming diet H versus diet L. No difference (P>.05) was detected between treatments in any skeletal growth variable measured. P hosphorus balance and digestibility did not differ significantly between tr eatments across d of age. However, digestibility of P was lower (P<.05) at d 240 and 330 compared to d 150 in both treatments. Horses consuming diet L experienced an increased (P<.05) urinary and a decreased (P<.05) fecal exc retion of Ca compared to horses consuming diet H. Apparent daily Ca balance was higher (P<.05) in horses consuming diet L than those on diet H at 240 and 330 d of age. Furthermore, Ca digestibility decreased significantly bet ween d 150 and d 240 and 330 in horses consuming diet H. Horses consuming d iet L experienced no difference (P>.05) in Ca digestibility across d of age . These findings suggest that horses consuming a low DCAD diet are able to co mpensate for the increased urinary excretion of Ca by enhancing intestinal Ca absorption and thereby increasing daily Ca balance and digestibility.