True Digestibility of Phosphorus in Different Resources of Feed Ingredients in Growing Pigs

To determine the true digestible phosphorus (TDP) requirement of growing pigs, two experiments were designed with the experimental diets containing five true digestible P levels (0.16%, 0.20%, 0.23%, 0.26% and 0.39%) and the ratio of total calcium to true digestible P (TDP) kept at 2:1. In Experiment 1, five barrows (Duroc×Landrace×Yorkshire) with an average initial body weight of 27.9 kg were used in a 5x5 Latin-square design to evaluate the effect of different dietary P levels on the digestibility and output of P and nitrogen. In Experiment 2, sixty healthy growing pigs (Duroc×Landrace×Yorkshire) with an average body weight (BW) of 21.4 kg were assigned randomly to one of the five dietary treatments (12 pigs/diet), and were used to determine the true digestible phosphorus (TDP) requirement of growing pigs on the basis of growth performance and serum biochemical indices. The results indicated that the true digestibility of P increased (p 0.05) among the five diets, with the average nitrogen output of 12.14 g/d and nitrogen retention of 66% to 74% (p>0.05), which suggested that there was no interaction between dietary P and CP protein levels. During the 28-d experimental period of Experiment 2, the average daily gain (ADG) of pigs was affected by dietary TDP levels as described by Eq. (1): y = -809,532x4+788,079x3-276,250x2+42,114x-l,759; (R 2 = 0.99; p<0.01; y = ADG, g/d; x = dietary TDP, %), F/G for pigs by Eq. (2): y = 3,65l.lx4-3,480.4x 3 +1,183.8x 2 -172.5x+10.9 (R 2 = 0.99; p<0.01; y = F/G; x = dietary TDP, %), and Total P concentrations in serum by Eq. (3): y = -3,311.7x 4 +3,342.7x 3 -1,224.6x 2 +195.6x-8.7 (R 2 = 0.99; p<0.01; y = total serum P concentration and x = dietary TDP, %). The highest ADG (782 g/d), the lowest F/G (1.07) and the highest total serum P concentration (3.1 mmol/L) were obtained when dietary TDP level was 0.34%. Collectively, these results indicate that the optimal TDP requirement of growing pigs is 0.34% of the diet at a total Ca to TDP ratio of 2:1.