In situ method to compare conversion coefficients of crude protein to metabolisable protein in poultry by-product meal, roasted soybean and fishmeal

The amount of nitrogen obtainable from the slaughterhouse wastes was 22.36 kg per 1,000 head which could be an excellent biological source of nitrogen (protein) in animal nutrition. The poultry by-product meal (PBM) is one of the most important rendering by-product with a high protein content for use to feed ruminants. It has been reported previously that including PBM as protein substitute for soybean meal (SBM) could decrease feed costs in growing hair lambs. However, a better understanding of the chemical composition and protein degradation patterns of PBM would be very useful in improving the accuracy of formulation of animal diet. Among the chemical analysis clearing the protein quality, the evaluation of metabolisable protein of feedstuffs could help in more precise ration formulation especially in protein-rich by-products. Soybean as well as fish meal are two commonly used protein sources in ruminant nutrition. Evaluation and comparison of MP for different protein sources in ruminant nutrition bring this opportunity for replacement the feedstuffs instead of each other. There are different methods to identify the coefficient of crude protein convert in to metabolisable protein. Each method have robustness and weakness as well. This study was carried out to estimate and compare the crude protein to metabolisable protein (MP) conversion coefficients of poultry by-product meal, roasted soybean (RSB) and fish meal (FM) by in situ method.
The experiment was conducted on three male rumen cannulated Ghezel sheep which allocated in Latin Square change over design. The sheep were fed two times daily on 0800 and 1400 h. The basal diet was consisted of 50, 35 and 15% of alfalfa hay, barley and a composition of three experimental feedstuffs (PBM, SB, and FM), respectively. The in situ experiment was done with incubation times on 4, 8, 16, 24, 36 and 48 h. The crude protein for all incubation times were measured. The slow degradable and fast degradable fractions of protein contents were estimated based on in situ experiment. The fractionating of protein based on Cornell net carbohydrate and protein system (CNCPS) was carried out as well. Phosphate buffer soluble nitrogen was measured using phosphate buffer. Neutral detergent insoluble nitrogen and acid detergent insoluble nitrogen (ADIN) were determined as nitrogen content of residual after neutral and acid detergent procedures, respectively. B2 fraction calculated by difference and results were presented as percentage of CP. The degradation profiles were calculated by the nonlinear model described by Ørskov and McDonald (1979). The effective degradability (ED) in the rumen was calculated, ED = a [(b × c)/ (c k)], using NEWAY software; where "a" is the water-soluble fraction, "b" the potentially degradable fraction, "c" degradation rate of parameter "b", and "k" the passage rate of the digesta out of the rumen. Then metabolisable protein estimation as well as rumen degradable and undegradable contents of the protein in different experimental feedstuffs were calculated based on in situ data.
The chemical analysis of the experimental feedstuffs results show that the greatest protein content was for fish meal. The protein content of PBM was obtained 561 g/kg. The protein content of PBM was similar as previous reports. The ether extract of the PBM was however the greatest value among treatments. Because most of the ether extract refusal was included in PBM, so this fraction was greater than that of those observed for FM and RSB. The CNCPS fractionation of different PBM sources clear that except than that of “A” fraction all the fractions were differed among samples. This shows the huge difference for different sub-samples of this byproduct. This suggests to do the chemical abalysis for PBM before using as feedstuff in animal nutrition. Regarding the degradability trail results suggest that the parameter (a) was 76.6, 98.2 and 79.2% for PBM, RSB and FM, respectively (P The results of this study indicated that, lowering the content of ADIN from poultry byproducts through the different forms of processing may improve protein efficiency and consequently cause improvement in CP to MP conversion coefficient. Improving the protein quality of PBM may make it a suitable replacement feeding instead of commonly used protein sources in ruminant nutrition.