Aspects of Phosphorus Nutrition in Swine
Scott R. Baker
2010
Three experiments were conducted to evaluate aspects of phosphorus nutrition in pigs. The first 2 experiments were conducted to determine the proper methodology for determining the utilization of P in pigs. The relative bioavailability procedure that uses a slope ratio method was compared with the total tract digestibility method. The 2 experiments were carried out to compare the relative bioavailability (RBV) values of P in dicalcium phosphate (DCP) and distillers dried grains with solubles (DDGS) with the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of the same ingredients. In Exp 1, eighteen growing pigs (initial BW; 34.93 ?? 1.04 kg) were allotted to 3 cornstarch-based diets and housed individually in metabolism cages. One diet was a P-free diet that was used to determine endogenous P losses (EPL). Two additional diets in which DCP or DDGS was the sole source of P were also formulated. Results showed that the ATTD of P in DCP and DDGS were 86.1 and 58.8%, respectively. The EPL was determined to be 174 mg/kg DMI and the STTD of P was calculated to be 93.1% in DCP and 63.1% in DDGS. In Exp 2, forty two pigs (initial BW: 29.02 ?? 2.03 kg) were allotted to 7 diets and housed individually. A basal diet (0.22% P) was formulated and 3 additional diets were formulated by adding 0.04, 0.08, or 0.12% P from DCP to the basal diet. The remaining 3 diets were formulated by adding 0.04, 0.08, or 0.12% P from DDGS to the basal diet at the expense of cornstarch. The animals were fed their respective diets for 28 d and they were then euthanized. The third and fourth metacarpals were removed from the front right foot of the animals. Metacarpal bone ash and bone P were regressed against P intake for each ingredient using the slope ratio method. It was determined that the bioavailability of P in DDGS was 60% relative to that in DCP. It was concluded that there was good agreement between values for RBV and STTD values. In Exp 3, the effect of BW on EPL and nutrient digestibility was determined. A semi-purified P-free diet was formulated to determine EPL. Three additional diets containing soybean meal (SBM), DDGS, and corn as sole source of P were also formulated. Twenty-four barrows (initial BW: 9.66 ?? 0.67 kg) were allotted to the 4 diets and placed in metabolism cages for five 12-d collection periods. Pigs had an average BW of 9.66 ?? 0.67, 22.29 ?? 2.57, 53.77 ?? 9.91, 92.73 ?? 16.17, and 129.23 ?? 18.55 kg at the start of each collection period. Pigs were fed the same diet during all collection periods, but between collection periods they were fed a corn-soybean meal-DDGS diet. During the collection periods fecal samples were collected quantitvely from d 6 to 11 and values for ATTD, EPL, and STTD of P and ATTD of Ca, GE, CP, ether extract, ADF, NDF, and ash were calculated. There was no effect of BW on EPL and the average EPL was 220 mg/kg DMI. The ATTD and STTD of P in SBM and corn increased (linear, P 0.05) of BW on the ATTD of ADF, NDF, and Ca. For the DDGS diet, there was an increase in the ATTD of GE, NDF, and CP (linear and quadratic, P 0.05) of pig BW on the ATTD of GE, ether extract, or Ca. It was concluded that the ATTD and STTD of P in corn and SBM, but not in DDGS, increases as the pig BW increases, but EPL of P is constant regardless of pig BW. The influence of pig BW on the ATTD of GE and nutrients is dependent on the diet
