Protein quality assessment of feed ingredients for poultry is often achieved using in vitro or in vivo testing. In vivo methods can be expensive and time consuming. Protein quality can also be evaluated using less expensive and time consuming chemical methods, termed in vitro. These techniques are used to improve the user’s efficiency when dealing with large sample numbers, and some mimic the physiological and chemical characteristics of the animal digestive system to which the ingredient will be fed. The pepsin digestibility test is the in vitro method of choice for quick evaluation of protein sample during quality control and in most research settings. Even though the pepsin digestibility test uses enzymes to liberate the amino acids from the protein, it does not mimic normal in vivo digestive conditions. The results obtained with this method may be misleading if the samples tested contain fats or carbohydrates which they often do. Multi-enzyme tests have been proposed to overcome the problem encountered when using the pepsin digestibility test. These tests use a combination of enzymes in one or multiple steps customized to simulate the digestive process of the animal. Multi enzyme assays can predict animal digestibility, but any inherent biological properties of the ingredients on the animal digestive tract will be lost.

It is difficult to obtain in vivo digestion kinetics data of high protein ingredients using chickens. Collecting kinetics data requires repeated sampling of digesta from the small intestine during the digestion process, which is not easily accomplished due to the anatomical structure of chicken digestive tract. An in vitro technique is proposed for measuring the digestion kinetics of protein sources fed to chickens. The method has a 30 min gastric and 3 h intestinal phase. Five hundred milligram crude protein (CP) equivalent of each meal sample (CP = % N × 6.25) was digested with pepsin (28,260 units) in 50 mL polyethylene centrifuge tubes for 30 min in a shaking water bath (150 strokes/min; 30 mm stroke length) at 41 °C. The 6.5 mL pancreatin was selected as the enzyme concentration for the intestinal phase, during which time 500 μL aliquots were collected at 0, 15, 30, 45, 60, 90, 120, 150, 180 and 240 min. Samples were diluted 1:820 with HCl and sodium acetate buffer, and then mixed with ninhydrin reagent (2:1) at 100 ± 2 °C for 15 min and spectrometric readings taken at 568 nm. To validate the assay, 5 replications of soybean meal (SBM), corn gluten meal (CGM), corn distillers dried grains with solubles (CDDGS), porcine meal (PCM), fish meal (FM) and casein (CA) were digested. The digestion data were modeled with PROC NLIN procedure, and the intra coefficient of variation (CV) assessed using PROC MEANS of SAS 9.4. The digestion values at 180 min were SBM 95 ± 4, FM 93 ± 3, PCM 68 ± 4, CGM 82 ± 3 and CDDGS 70 ± 2. Intra CV for SBM, CGM, CDDGS, PCM and FM were 5%, 5%, 12%, 10% and 2%, respectively. The estimated fractional digestion rates for SBM, CGM, CDDGS, FM and PCM were 0.023, 0.013, 0.009, 0.024 and 0.013, respectively. In conclusion, the proposed in vitro technique estimated the rate and extent of the digestion of CP for the meals with low intra CV.

The rate and extent of protein digestion are relevant to broiler performance and health, but information is lacking on the rate of digestion and the

High dietary protein and the use of poorly digested protein sources have been suggested to negatively impact broiler health, possibly because of prot