221 In Vitro Prediction of Standardized Total Tract Digestibility of Phosphorus Among Sources of Animal Protein Meals. (10th April 2018) - Zhu, J
Abstract: In vitro digestibility of phosphorus (P) was determined in 13 sources of animal protein meals (2 blood meals, 1 chicken meal, 1 chicken byproduct meal, 2 feather meals, 2 meat meals, 3 meat and bone meals, 1 poultry by-product meal, and 1 poultry meal), and a mathematical model was developed to estimate the economic benefit of formulating diets with a more accurate P digestibility values of ingredients. In vitro enzymatic hydrolysis was conducted using a two-step assay in which pepsin and pancreatin were used to mimic gastric and small intestinal digestion. The amount of total P released by enzymatic digestion was analyzed by the ascorbic acid method. All assays were repeated 6 times. Data of in vitro P digestibility were analyzed using the GLM procedure in SAS. A simple linear regression analysis was conducted between in vitro P digestibility data and in vivo standardized total tract digestibility (STTD) of P, which was calculated based on apparent total tract digestibility in pigs from their respective sources from a previous experiment. Chicken meal had lower ( P < 0.01) in vitro P digestibility (42.98%) compared with chicken by-product meal (62.24%), and there were no differences ( P > 0.10) between poultry meal (33.52%) and poultry byproduct meal (32.21%). The average in vitro P digestibility of 3 sources of meat and bone meal was 33.21 ± 0.24%, and the average of 2 meat meal sources was 35.99 ± 1.56%. Animal protein meals with greater Ca:P tended to have a lower in vitro digestibility of P ( in vitro P digestibility, % = -30.14 × Ca:P + 91.18; R 2 = 0.89). There was also a high correlation between in vitro P digestibility and in vivo STTD of P (STTD of P, % = 1.00 × in vitro P digestibility + 1.33; R 2 = 0.91). The mathematical model showed that when P digestibility is overestimated by 10% compared to its actual value in an ingredient, pigs fed P deficient diets may have a 30 g less average daily gain than pigs fed diets formulated with more accurate values from the in vitro assay. When P digestibility of ingredients is underestimated by 10% compared to its actual value, the cost of the feed may increase by $0.55/pig. These results suggest that the 2-step in vitro P digestibility assay can be used to reasonably predict in vivo P digestibility of animal protein by-products fed to swine.