In Vitro Methods of Assessing Protein Quality for Poultry.

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.

The influence of indigestible protein on broiler digestive tract morphology and caecal protein fermentation metabolites.

Indigestible dietary protein fermentation products have been suggested to negatively influence broiler performance due to their impact on health and digestive tract morphology. This study evaluated the digestive tract morphology and caecal protein fermentation metabolites of broiler fed 3 dietary protein levels (24%, 26% and 28%) with low or high indigestible protein (LIP, HIP). Two completely randomized 3 × 2 factorial trials were conducted with protein level (PL) and indigestible protein (IDP) as the main factors. In both trials, birds received six diets (24-LIP, 24-HIP, 26-LIP, 26-HIP, 28-LIP and 28 HIP) formulated with no medication. On day 5, trial 1 birds were vaccinated with Coccivac-B52, while trial 2 received no vaccine. Tissue and caecal samples were collected and caecal contents analysed for fermentation metabolites. Differences were considered significant when p ≤ .05. The LIP treatment caecal content in trial 1 at 14 days had greater histamine, agmatine and cadaverine levels, while HIP diets resulted in increased serotonin, tryptamine and spermidine. Histamine, serotonin and tryptamine at day 28 were not affected by IDP, and ammonia was not affected by treatments at day 14 or day 28. At day 14, HIP birds had lower total short-chain fatty acids, higher caecal pH and heavier pancreas, proventriculus, gizzard, jejunum and ileum weights. The same effects of IDP found in trial 1 were observed for histamine, agmatine, cadaverine, serotonin, tryptamine and spermidine at day 21 in trial 2. Trial 2 had a PL-by-IDP interaction influencing tyramine, spermidine (28-LIP > 24-LIP) and spermine with values increasing with PL for LIP diets and remaining constant for HIP diets. An interaction between PL and IDP was found for ammonia level and was similar to interactions for biogenic amines. In conclusion, dietary PL and IDP influence broiler caecal protein fermentation metabolites and those effects varied with coccidiosis vaccination and rearing environment.

Effect of protein sources on performance characteristics of turkeys in the first three weeks of life.

The effect of nutrition during the early life of turkey poults has a long-lasting impact on bird performance. This study assessed the digestibility of 5 high protein feed ingredients (soybean meal [SBM], corn gluten meal [CGM], canola protein concentrate [CPC], fish meal [FM], and porcine meal [PCM]) in broiler chickens, as well as their use in turkey pre-starter diets fed to 21 d of age. The first experiment (5 × 2 factorial arrangement) determined nitrogen corrected apparent metabolizable energy (AMEn) and apparent ileal amino acid digestibility (AIAAD) of each ingredient in broiler chickens at 5 and 21 d of age, using 6 replications of 30 and 8 chicks, respectively. In the second experiment (completely randomized design), 4 replication pens, containing 23 d-old poults, were randomly assigned to one of 5 dietary treatments. The diets were formulated based on the AMEn and AIAAD values derived in the first experiment, and consisted of a high SBM control diet, and 4 additional diets with either CPC, FM, PCM or CGM replacing 25% of the protein supplied by SBM in the control diet. Statistical analysis was completed using Proc Mixed in SAS 9.3. Planned contrasts were used to compare treatments in the second experiment. Trends were identified at P < 0.10 and significant differences identified at P ≤ 0.05. Bird age did not affect CPC, FM, CGM, and SBM AMEn, but the PCM value at d 5 was higher than that at d 21. Apparent ileal amino acid digestibility increased with age for most amino acids (AA), but the response was AA and protein source dependent. The largest average increase in AIAAD between 5 and 21 d of age was observed for CGM. Inclusion of CPC, FM, PCM, or CGM increased body weight up to 14 d, in comparison to poults fed the SBM diet, but feed efficiency and water consumption were not affected. Terminal ileum digesta moisture values were higher for birds fed SBM when compared to those fed PCM. These results demonstrate that combining SBM with CPC, FM, PCM, or CGM improves poult performance during the first 14 d of life in comparison to feeding SBM alone.

Development of an in vitro protein digestibility assay mimicking the chicken digestive tract.

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.