Dietary Factors Affect The Determination Of True Phosphorus Digestibility For Broiler Chickens

Poultry production has been raised more rapidly than other meat producing animal industry,because of higher consumer demand and lower cost.Broilers are used as meat purpose as they are the ideal protein supplier to humans,but their production faces many nutritional problems due to feed formulation and nutrients requirements.Phosphorus(P)is an essential macro-mineral nutrient required for body growth,bones development,and genomic functions.The main components of broilers diets are the plant origin feedstuffs,which contain anti-nutritional factors like phytic acid or phytate.The phytate phosphorus(PP)digestibility and utilization is low in the gut of birds,resulting in decreased digestibility of other nutrients and increased fecal excretion of P,which causes challenges to the entire ecosystem.Scientists observed that the apparent prececal digestibility(APD)was affected by dietary factors and cause large endogenous P losses(EPL).Scientists further suggested that the true prececal digestibility can reflect actual digestion and absorption of P.Therefore,understanding the effects of dietary factors on P digestibility and precisely determining the true phosphorus digestibility(TPD)in chickens is helpful for formulating an eco-friendly diet.The dietary calcium to phosphorus(Ca:P)ratio,protein source,and P source have been recognized as important dietary factors influencing APD,but little information is about their effects on TPD of chickens.Hence,the main objective of the present study is to investigate the effects of above-mentioned dietary factors on TPD in a broiler model using linear regression method.To achieve our goals,four trials were designed.The 1st experiment was conducted to evaluate the TPD of P in soybean meal(SBM)for broiler chickens fed diets with different Ca:P using the regression method.A total of 768 male Ross(708)broilers were allocated to 12 dietary treatment groups according to a randomized complete block design in a 4×3 factorial arrangement.The 4 levels of dietary Ca:P ratios(0.8,1.2,1.6,2.0)and 3 levels of SBM(34.0,47.0,60.0%).The results showed that the body weight(BW)gain,feed intake,feed efficiency,and dry matter(DM)digestibility was affected by dietary SBM levels(P<0.05).The BW gain,feed intake,feed efficiency,and DM digestibility increased linearly with increasing SBM level independent of Ca:P ratio(P<0.05).Furthermore,there were linear increases in prececal P output,prececal digested P,and APD in each dietary Ca:P ratio(P<0.05).Chickens fed diets of Ca:P ratio of 0.8 and 1.2 the prececal digested P and APD of P increased quadraticaly(P<0.05).Birds fed the diets at Ca:P ratio of 0.8 exhibited higher TPD of P in SBM than birds fed diets with other Ca:P ratios(P<0.05).In conclusion,the low dietary Ca:P ratio(0.8)increased the true prececal digestibility of P for broiler chickens.The 2nd experiment was conducted to determine the TPD of P fed diets with high or low P levels for broiler chickens by using the regression method.A total of 384 male Ross(708)broiler chicks were assigned into 6 diets of a randomized complete block design.The 6 dietary treatments in a 2×3 factorial arrangement consisted 2 dietary P levels(1.03 to 2.35 and 2.46 to 3.68 g/kg)and 3 graded SBM levels(14.0,25.0,36.0 g/kg).The results showed that the dietary P levels and SBM levels have affected the body BW gain,feed intake,the ratio of gain to feed and prececal DM digestibility(P<0.05).When chickens fed low and high P diets.,there were linear increases in BW gain,feed intake,feed efficiency,prececal P output,and prececal digested P(P<0.05).Furthermore,chickens fed low P diet had quadraticaly increased APD as dietary SBM level increased(P<0.05),whereas the linearly increased APD,was observed in chickens fed with high P diet(P<0.05).The predictive value of TPD for chickens fed low P diets was higher than the birds fed high P diets(P<0.05).In summary,the TPD of P in SBM for broiler chickens were higher fed low-P diet.The 3rd experiment was conducted to compare the regression driven estimates of TPD of P in SBM for broiler chickens fed diets with or without casein supplementation at moderate or low total phosphorus concentration.A total of 768 male Ross(308)broilers were allocated to 12 diets in a 2x2x3 factorial arrangement of two total P concentration(moderate-P or low-P),two diet types(with or without casein)and three SMB levels(low,medium or high).The results showed that the dietary casein supplementation improved BW gain,feed intake,and feed efficiency of broilers(P<0.05).Broilers fed the moderate-P diets had greater dietary total P intake,prececal flow and total tract output of P,prececal digested P and total tract retained(TTR)P compared with birds fed the low-P diets(P<0.05).Broilers fed the moderate-P diets had a linear increase in APD and TTR of P(P<0.05).Regression of prececal digested P showed that chickens fed the moderate-P diets had lower estimates of TPD of P in SBM than that for chickens fed the low-P diets(P<0.05),while dietary casein supplementation had no effects on the determined values of TPD of P.In conclusion,the dietary total P concentration affects the estimates of TPD of P determined by regression approach.The 4th experiment was designed to estimate the TPD fed diets at low and adequate crude protein(CP)levels.A total of 384 male broilers were assigned into 6 diets in a 2x3 factorial arrangement.There were 2 dietary CP levels and 3 dietary total P levels.The results showed that the BW gain,feed intake feed efficiency,and DM digestibility was affected by the dietary CP level(P<0.05).Furthermore,the prececal P output and prececal digested P linearly increased for the chickens fed low and adequate CP diets(P<0.05).There were no differences in the estimates of TPD of P between chickens fed the low and adequate CP diets.In summary,the dietary CP levels have no effects on the TPD of P for broiler chickens.Dietary factors,which contain Ca:P ratio,P level,casein supplementation,and CP level,were included in four trials to test the dietary effects on TPD of broiler chickens by using the linear regression method.In this study,broilers fed a diet with lower Ca:P ratio or lower P levels resulted in increased TPD of P.Dietary casein supplementation and crude protein level had no effect on the TPD of P.Furthermore,the supplementation of Ca,P,casein,and crude protein in diet improved the phosphorus digestibility and growth performance of broilers and decreased the P fecal excretion,which is eco-friendly for the poultry industry.