ABSTRACT
The objective of this experiment was to test the hypothesis that increasing dietary phytase reduces basal endogenous loss of Ca and increases P balance in pigs. Seventy barrows (initial body weight: 17.66 ± 1.69 kg) were allotted to seven Ca-free diets using a randomized complete block design with two blocks and five pigs per diet in each block. All diets were based on corn, potato protein concentrate, and full-fat rice bran. A positive control (PC) diet was formulated to contain P at the requirement for standardized total tract digestible (STTD) P by 11 to 25 kg pigs. Six negative control (NC) diets were formulated by reducing the provision of digestible P by 0.15% and adding 0, 250, 500, 1,000, 2,000, or 4,000 phytase units/kg diet. Pigs were housed individually in metabolism crates that allowed for total, but separate, collection of urine and feces. Daily feed allowance was 3.0 times the maintenance requirement for metabolizable energy and was divided into two equal meals. Diets were fed for 12 d with the first 5 d considered the adaptation period. Urine collections started on day 6 in the morning and ceased on day 10 in the morning. Fecal markers were also included in the morning meals on day 6 and day 10 and feces were collected according to the marker-to-marker procedure. Results indicated that the apparent total tract digestibility of dry matter was not affected by dietary P or phytase levels. The basal endogenous loss of Ca was not affected by dietary P, but exponentially decreased (P = 0.030) as phytase level increased in the diets. Phosphorus retention (g/d) and standardized total tract digestibility of phosphorus were greater (P < 0.05) in pigs fed the PC diet compared with pigs fed the NC diet with no phytase. The STTD of P exponentially (P < 0.001) increased as phytase level increased in the diets, but because of the lack of Ca, retention of P (% of absorbed) linearly decreased (P = 0.006) as phytase increased. In conclusion, basal endogenous loss of Ca decreased as dietary phytase increased demonstrating that endogenous Ca can be bound to phytate in the intestinal tract of pigs. However, STTD of P increased as phytase level in the diets increased.
Phytate in plant-based ingredients limits the amount of phosphorus available for absorption and can form indigestible complexes with endogenous calcium. However, breakdown of the phytate molecule by phytase increases digestibility of phosphorus and may also reduce endogenous loss of calcium. Therefore, the objective of this experiment was to test the hypothesis that level of phytase influences the utilization of phosphorus and basal endogenous loss of calcium in growing pigs fed calcium-free diets. Results demonstrated that total tract digestibility of phosphorus increased as phytase increased in the diets, but not all of the absorbed P was retained in the pigs due to a lack of calcium. Dietary concentration of phosphorus did not affect basal endogenous loss of calcium, but increasing concentrations of microbial phytase reduced basal endogenous loss of calcium. These results demonstrate that some endogenous calcium is bound to phytate, but including microbial phytase in diets helps release this calcium and therefore reduce endogenous loss of calcium.
