An in vitro model for caecal proteolytic fermentation potential of ingredients in broilers

Fermentation of protein in the caeca of chickens may lead to the production of potentially detrimental metabolites, which can reduce gut health. A poor precaecal digestion is expected to increase protein fermentation (PF), as more proteins are likely to enter the caeca. It is unknown if the undigested protein that enters the caeca differs in fermentability depending on their ingredient source. In order to predict which feed ingredients increase the risk of PF, an in vitro procedure was developed, which simulates the gastric and enteric digestion, subsequent caecal fermentation. After digestion, amino acids and peptides smaller than 3.5 kD in the soluble fraction were removed by means of dialysis. These amino acids and peptides are assumed to be hydrolysed and absorbed in the small intestine of poultry and therefore not used in the fermentation assay. The remaining soluble and fine digesta fractions were inoculated with caecal microbes. In chicken, the soluble and fine fractions enter the caeca, to be fermented, while insoluble and coarse fractions bypass them. The inoculum was made N-free to ensure bacteria would require the N from the digesta fractions for their growth and activity. The gas production (GP) from the inoculum, therefore, reflected the ability of bacteria to use N from substrates and was an indirect measure for PF. The Maximum GP rate of ingredients averaged 21.3 ± 0.9 ml/h (mean ± SEM) and was in some cases more rapid than the positive control (urea, maximum GP rate = 16.5 ml/h). Only small differences in GP kinetics were found between protein ingredients. Branched-chain fatty acids and ammonia concentrations in the fermentation fluid after 24 hours showed no differences between ingredients. Results indicate that solubilised undigested proteins larger than 3.5 kD are rapidly fermented independent of its source when an equal amount of N is present.

The effects of coarse and wet feeding on performance parameters, gastrointestinal tract and tibia traits, and digesta phytase activity in egg-type pullets, either fed a low or moderate phosphorus diet

In a 2 × 2 × 2 factorial design, the effects of dietary non-phytate phosphorus (NPP) levels, 0.17% (low) and 0.33% (moderate), diet moisture (dry and wet), and diet particle size (coarse and fine), were studied on egg production, characteristics of gastrointestinal tract (GIT) and tibia, digesta pH, and phytase activity in layer pullets (16 to 28 wk of age). The low NPP diet increased average daily water intake (ADWI) to ADFI ratio (4.2%) from 16 to 17 wk, but decreased this ratio (2.8%) from 23 to 27 wk. It decreased ADFI (1.5%) and egg mass production (3.8%) from 19 to 22 wk. It decreased egg weight (0.29 g) and ADWI (2.1%) from 23 to 27 wk. At 22 wk, the GIT relative empty organ weights were (g/kg BW) higher for proventriculus + gizzard (0.96), duodeneum (0.94), and jejunum + ileum (1.95) with the low vs. moderate NPP diet. The low NPP diet decreased digesta phytase activity in crop and proventriculus+gizzard at 28 wk. The wet diet increased ADFI, ADWI, and ADWI/ADFI ratio from 16 to 27 wk, egg mass production (3.0%) from 19 to 22 wk, and egg weight (0.45 g) from 23 to 27 wk. The wet diet also increased digesta phytase activity in proventriculus+gizzard. The coarse diet decreased ADFI from 19 to 22 wk (1.7%) and 23 to 27 wk (1.2%). The coarse diet caused reduced egg mass production (2.6%) from 23 to 27 wk. Egg shell breaking strength was increased on the coarse diet (0.9 Newton). The coarse diet increased ADWI/ADFI ratio from 16 to 27 wk, and increased relative gizzard weight by 1.95 and 0.81 g/kg BW at 22 and 28 wk, respectively. The coarse diet increased jejunal/ileal pH with 0.16 units at 28 wk. None of the tested parameters affected tibia characteristics. It was concluded that a low NPP diet did not clearly affect the studied parameters. The wet diet increased ADFI, ADWI, and egg production. The coarse diet increased ADWI, egg shell breaking strength, relative gizzard weight, and reduced ADFI and egg production.