The relationship between protein and phosphorus digestion and retention in growing pigs and broiler chickens

Xue, Pengcheng. Ph.D., Purdue University, December 2016. The Relationship between Protein and Phosphorus Digestion and Retention in Growing Pigs and Broiler Chickens. Major Professor: Dr. Layi Adeola. The objective of this study was to investigate the relationship between protein and P digestion and retention in growing pigs and broiler chickens. The methodology of determining the digestibility of AA and P and the effect of dietary N and P on the digestion and retention of these two nutrients were investigated. An experiment was conducted in growing pigs to investigate the additivity of AID or SID of CP and AA in mixed diets containing multiple protein sources. Using the determined AID or SID for CP and AA in corn, SBM, DDGS, and canola meal, the AID or SID for 4 mixed diets was predicted and compared with determined AID or SID, respectively. Eighteen growing pigs (initial BW = 61.3 ± 5.5 kg) with surgically fitted T-cannula were assigned to a duplicated 9 × 4 incomplete Latin square design with 9 diets and 4 periods. A nitrogen-free diet was included to estimate basal ileal endogenous loss of AA; 4 semi-purified diets to determine the AID and SID of CP and AA in the 4 ingredients; and 4 mixed diets to test the additivity of AID and SID. The results substantiate the notion that SID of AA are more accurate than AID for predicting ileal digestibility of AA in mixed diets containing multiple protein sources. To determine the TTTD of P in triticale DDGS for growing pigs with or without phytase using the regression method, six diets were formulated in a 3 × 2 factorial arrangement, including 3 levels of triticale DDGS (300, 400, or 500 g/kg) and phytase (0 or 500 FTU/kg of diet). A total of 48 barrows (initial BW 22.2 ± 1.3 kg) were assigned to the 6 diets in a randomized complete block design. There was a 5-d adjustment period followed by a 5-d total collection of feces. The results indicated that phytase improved ATTD of P in triticale DDGS (P \u3c 0.001). In diets without added phytase, the ATTD of P in triticale DDGS was 65.0, 67.7, and 63.2% for the diets with 300, 400, and 500 g/kg triticale DDGS, respectively; the corresponding values for diets with added phytase were 77.3, 76.3, and 75.7%.The TTTD of P was estimated at 75.4% for triticale DDGS or 81.1% with added phytase, respectively. The difference between the TTTD with or without phytase was not statistically significant. For triticale DDGS, the supplementation of 500 FTU/kg phytase in the diet could increase the ATTD of P (P \u3c 0.001), but not the TTTD of P. The effect of dietary CP concentrations on ileal P digestion in growing pigs was investigated in the third study. A total of 18 ileal-cannulated pigs (initial BW 44.2 ± 3.2 kg) were used in a duplicated 9 × 3 incomplete Latin Square design, with 9 treatments and three 7-d experimental periods giving 6 replicates per treatment. The 9 treatments consisted of 1 nitrogen-free diet to estimate basal endogenous loss of AA, and 8 corn-soybean meal-based diets in a 2 × 4 factorial arrangement, which included 2 CP concentrations (6.9 or 13.4%) and 4 ATTDP concentrations (0.09, 0.16, 0.24, or 0.32%). Low CP diets limited ileal digested P (g/kg•DMI) (P \u3c 0.05). The ileal digested P (g/kg•DMI) increased linearly (P \u3c 0.01) with increasing ATTDP concentrations in the low CP group, but the pattern was linear (P \u3c 0.01) and quadratic (P \u3c 0.01) in the high CP group. In the low and high CP diets, the determined true ileal digestibility of P in mono-calcium phosphate was 54.4% and 75.6%, respectively. In conclusion, this research indicated that the ileal digestion of P could be limited by protein deficiency. Thus dietary CP concentration should be considered in P digestibility related studies. The quantitative relationship between N and P digestion and retention in broiler chickens and growing pigs was determined in the last two studies. In the broiler chicken study, a total of 384 14-d-old male broiler chickens were used in a randomized complete block design with 8 treatments and 6 replicates per treatment in a 7-d experimental period. There were 8 corn-soybean meal-based diets in a 2 × 4 factorial arrangement, which included 2 CP concentrations (10.7 or 21.5%) and 4 ATTDP concentrations (0.18, 0.32, 0.45, or 0.59%). Results showed that low dietary CP concentration limited growth performance (P \u3c 0.01), pre-cecal digestion and total tract retention of P (P \u3c 0.01), and NaPi-IIb gene expression ( P \u3c 0.05). Pre-cecal digestion and total tract retention of P (g/kg DM intake) linearly increased (P \u3c 0.01) with increasing ATTDP concentrations in both low and high CP groups. In conclusion, this study suggests an interrelationship between N and P digestion such that CP deficiency decreased the growth performance of birds consequently reducing pre-cecal P digestion in broiler chickens. Total tract retention of CP and P are linked with each other and body tissue growth may be a driver of the deposition of these two nutrients. In the growing pig study, a total of 72 growing pigs (initial BW 20.9 ± 0.8 kg) were used in a randomized complete blocked design, with 9 treatments and four 10-d experimental periods giving 8 replicates per treatment. The pigs were blocked by BW and allotted to 9 treatments with a 3 × 3 factorial arrangement consisting of 3 CP concentrations (5.5, 9.7, or 13.9%) and 3 ATTDP concentrations (0.11, 0.19, or 0.27%). The determined TTTD of P in MCP for the 5.5, 9.7, and 13.9% CP diets were 80.5, 82.6, and 87.9%, respectively. There were no statistical differences among the three TTTD estimates. In the nitrogen utilization results, increasing dietary P level decreased the urine nitrogen output (P \u3c 0.05). In conclusion, the results indicated that dietary CP deficiency may limit total tract P digestion and retention. Yet the quantitative relationship between total tract N and P retention remains unclear. In summary, the SID of most AA in corn, SBM, canola meal, and DDGS, are additive in complete diets. The regression method can be used to determine the true P digestibility and retention in feed ingredients for growing pigs and broiler chickens. Dietary CP deficiency can limit ileal and total tract P digestion. In broiler chickens, the retention of P is correlated with the retention of N. Yet in growing pigs this relationship has not been observed. Body weight gain might be the driving factor for the correlation between N and P retention in growing pigs and broiler chickens