Effects Of Feed Intake And Phosphorus Level On Estimating Standard Total Tract Digestibility Of Phosphorus In Growing Pigs

The present study was conducted to investigate the effect of dietary phosphorus（P）level and feed intake level on the estimation of standard total tract digestibility（STTD）for growing pig fed corn-and soybean meal（SBM）-based diet.Experiment 1: Fifty-six growing pigs（average initial body weight of 30.9±0.1 kg）were randomly divided into seven treatments.There were 8 replicates in each treatment with one pig per replicate.The 7 treatments were respectively composed of 7 different diets,where there is a P-free diet and 6 corn-and SBM-based diets that contained the assay ingredients of150,300,450,600,750 and 900 g/kg.Corn and SBM was mixed in the ratio of 3:2.Endogenous phosphorus loss（EPL）for growing pig was determined by feeding the P-free diet.The apparent total tract digestibility（ATTD）and STTD was calculated by the total collection procedure.The result showed that,with increasing P level in diets,ATTD of P had no significant effect（P > 0.05）,however,there was a liner increase in STTD of P（P < 0.01）.Experiment 2: Seventy-two growing pigs（average initial body weight of 41.2±0.8 kg）were divided into 9 treatments used in a randomized complete block design with 3×3 factorial arrangement.There were 8 replicates in each treatment with one pig per replicate.The experiment design contained 3 diets（P-free diet,low-P diet and moderate-P diet）and 3 feed intake（FI）levels（3%,4% and 5% of body weight）.The P-free diet was based on cornstarch.The low P diet and the moderate P diet were based on corn and SBM.Cornstarch was added into the low P diet to decrease the dietary total P level to 50% of the moderate P diet.Corn,SBM and dicalcium phosphate was the mainly dietary P source.The different treatments involved the P-free diet were used to estimate the value of EPL for growing pigs.The result indicated that daily basal EPL of growing pigs increased linearly with increasing FI level（P <0.05）,and the values of dietary P intake,fecal P output and digested P increased linearly in each diet（P < 0.01）.When growing pigs fed the low-P diet,dietary P intake,fecal P output,ATTD and STTD of P were significantly lower than in pigs fed the moderate-P diet（P < 0.01）.Despite of the P concentration in diets,increasing FI intake level led a markedly decrease in ATTD（P < 0.01）and STTD（P < 0.1）of P.With increasing FI level,there were a linearly decreases in ATTD and STTD of P for pigs fed the moderate-P diet（P < 0.01）,while there were no significant effects on ATTD and STTD of P for pigs fed the low-P diet（P > 0.1）.In conclusion,the STTD of P in low-P diet treatments was not affected by the increasing FI level,while the STTD of P in moderate-P diet group was significantly decreased with the increase of FI level.