Comparative digestibility and retention of calcium and phosphorus in normal- and high-phytate diets fed to gestating sows and growing pigs

The objective of this research was to test the hypothesis that calculated values for standardized total tract digestibility (STTD) and retention of Ca and P are not different between gestating sows and growing pigs. A total of 32 gestating sows (day of gestation = 40) and 32 castrates (body weight = 19.8 kg) were placed in metabolism crates. Two diets were formulated to contain 9.8 or 29.4 g/kg phytate. Diets were formulated based on corn, soybean meal, Ca carbonate, and dicalcium phosphate and the high-phytate diet also contained 400 g/kg full-fat rice bran. A Ca-free diet and a P-free diet were used to determine basal endogenous losses of Ca and P. Feces and urine were collected for 4 days after 4 days of adaptation. Results indicated that basal endogenous losses of Ca and P from gestating sows were greater (P < 0.05) than from growing pigs. The digestibility of dry matter was not affected by the physiological state of the animals, but was greater (P < 0.001) in the normal-phytate diet than in the high-phytate diet. Phytate level did not affect the STTD of Ca or Ca retention by gestating sows, but the STTD of Ca and Ca retention were greater if growing pigs were fed the normal-phytate diet than if they were fed the high-phytate diet (physiological state × phytate level interaction; P < 0.001). The STTD of P was greater for the normal-phytate diet than for the high-phytate diet, but the difference was greater for growing pigs than for gestating sows (physiological state × phytate level interaction; P = 0.002). Phosphorus retention by growing pigs fed the normal-phytate diet was greater than if they were fed the high-phytate diet, but P retention by gestating sows was not affected by phytate level (physiological state × phytate level interaction; P < 0.001). Regardless of phytate level, gestating sows had reduced (P < 0.001) STTD of Ca and P and reduced retention of Ca and P compared with growing pigs. In conclusion, gestating sows have reduced digestibility and retention of Ca and P, but increased basal endogenous losses of Ca and P, compared with growing pigs. Response to dietary phytate is different for STTD and retention of Ca and P between gestating sows and growing pigs. It may, therefore, not always be accurate to formulate diets for gestating sows using digestibility values for Ca and P that were obtained in growing pigs.