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Digestible phosphorus requirement of 20-kg pigs – A cooperative study
A 28-d cooperative study involving 10 experiment stations was conducted to determine the standardized total-tract digestible (STTD) P requirement of 20-kg pigs using broken-line regression analysis. Six concentrations of STTD P were fed to 1,032 pigs with an average initial BW of 19 kg in 240 pens (120 each of barrows and gilts). Monocalcium phosphate was added to a corn-soybean meal-based diet at the expense of cornstarch to establish the 6 concentrations of STTD P, ranging from 1.54 to 5.15 g/kg of diet, in increments of 0.62 g/kg. Limestone was added to maintain a constant Ca:total P at 1.5:1.0 among all diets. Average daily gain, ADFI, and G:F increased (P < 0.05) with increasing STTD P concentration for d 0 to 14, 14 to 28, and 0 to 28. From d 0 to 28, ADG and G:F increased (P < 0.01) from 639 to 809 g and 492 to 561 g/kg, respectively, as STTD P increased from 1.54 to 5.15 g/kg of diet. Barrows gained and ate more (P < 0.05) than gilts during d 14 to 28 and d 0 to 28. There was no interaction between gender and STTD P concentration for any of the growth performance response criteria. Metacarpal bone ash, Ca, and P increased (P < 0.01) from 45.6 to 52.6%, 17.6 to 19.9% and 8.0 to 9.6%, respectively, with increasing STTD P concentration. Furthermore, Ca and P in metacarpal ash, as well as metacarpal and femur mineral density and content increased (P < 0.01) with increasing STTD P concentration. The STTD P requirement determined by broken-line regression using ADG as a response variable was estimated to be 4.21, 3.45, and 3.87 g/kg of diet for pigs from d 0 to 14 (19 to 28 kg BW), d 14 to 28 (28 to 40 kg BW), and d 0 to 28 (19 to 40 kg BW), respectively. Using G:F, the corresponding estimates of STTD P requirement were 4.34, 3.71, and 4.06 g/kg of diet. The STTD P requirement (g/kg of diet) using mineralization response for metacarpus and femur ranged from 3.50 for P in metacarpal ash to 4.28 for femur mineral density. Using an average of the estimates derived from ADG and G:F, the mean STTD P requirement of pigs from 20 to 40 kg was determined to be 3.97 g/kg of diet.
Keywords: Phosphorus, pigs, standardized total tract digestible, requirement