Effects of dietary calcium : phosphorus ratios on apparent absorption of calcium and phosphorus in the small intestine, cecum, and colon of pigs

Thirty-two crossbred barrows were used to investigate the effects of dietar y Ca:total P (tP) ratios in phytase-supplemented diets on the apparent abso rption of P and Ca in the small intestine, cecum, and colon. Three Ca:tP ra tio treatments (1.5:1, 1.3:1, or 1.0:1) were created by adjusting the amoun t of ground limestone added to the basal low-P grower (.39% tP including .0 7% added inorganic P) and finisher (.32% tP without added inorganic P) diet s. All low-P ratio diets were supplemented with Natuphos phytase at 500 uni ts/kg. A positive control diet without phytase supplementation contained ad equate P and Ca to meet dietary requirements. At 123 kg, the pigs were slau ghtered and the contents of ileum, cecum, and colon were collected. Lowerin g the dietary Ca:tP ratio in the diets containing phytase linearly increase d (P < .01) the apparent absorption (% and g/d) of P in the small intestine , but Ca absorption was not affected. Pigs fed the low-P diet with a Ca:tP ratio of 1.0:1 had an apparent absorption (g/d) of P or Ca similar to that of pigs fed the control diet, which was adequate in Ca and P. Averaged acro ss all diets, the apparent absorption of P was highest when measured at the cecum, and the apparent absorption of Ca was highest when measured at the colon. In conclusion, lowering the dietary Ca:tP ratio to 1.0:1 in a low-P diet containing phytase increased the apparent absorption of P in the small intestine, Furthermore, a significant amount of P was absorbed in the cecu m.