Digestion dynamics in broilers fed rapeseed meal

Abstract

Rapeseed proteins are described to be poorly digestible in chickens. To further identify some molecular locks that may limit their use in poultry nutrition, we conducted a proteomic study on the various chicken digestive contents and proposed an integrative view of the proteins recruited in the crop, proventriculus/gizzard, duodenum, jejunum, and ileum for digestion of rapeseed by-products. Twenty-seven distinct rapeseed proteins were identified in the hydrosoluble fraction of the feed prior ingestion. The number of rapeseed proteins identified in digestive contents decreases throughout the digestion process while some are progressively solubilized in the most distal digestive segment, likely due to a combined effect of pH and activity of specific hydrolytic enzymes. Fifteen chicken proteins were identified in the hydrosoluble proventriculus/gizzard content, including chymotrypsin-like elastase and pepsin. Interestingly, on the 69 distinct proteins identified in duodenum, only 9 were proteolytic enzymes, whereas the others were associated with homeostasis, and carbohydrate, lipid, vitamin and hormone metabolisms. In contrast, chicken proteins identified in jejunal and ileal contents were mostly proteases and peptidases. The present work highlights the relevance of using integrative proteomics applied to the entire digestive tract to better appreciate the protein profile and functions of each digestive segment.

Figure 1

pH of the digesta within each digestive segment (Crop, Proventriculus/gizzard, Duodenum, Jejunum and Ileum). Means followed by distinct lowercase letters differ significantly (P < 0.05, refer to Methods).

Figure 2

Protein concentration of hydrosoluble fractions in each digestive segment (a) and relative content of the insoluble fraction (b). Protein concentration (mg/mL) of each insoluble fraction (group A only) was determined using Dc-Biorad Assay (Bio-Rad, Marnes-la-Coquette, France) as described in Methods. The remaining insoluble fraction obtained after centrifugation was expressed as a percentage of the initial weight (group A only).

Figure 3

SDS-PAGE analyses (a) and gelatin zymographies (b) of digestive contents (hydrosoluble fraction) along the chicken digestive tract. SDS-PAGE were performed under reducing/denaturing conditions (40 µg proteins). Zymographies were conducted under non-reducing/non-boiling conditions (5 µg of proteins) at physiological pH (pH = 5.3 for crop; 4.0 for prov./giz; 5.3 for duo., 6.2 for jejunum and 8.2 for ileum). A, B, C correspond to group A (t = 0 after the end of feeding), B (t = 1h30 after the end of feeding) and C (t = 3 h after the end of feeding), respectively. Prov./giz, proventriculus/gizzard; Duo., duodenum; Jej. Jejunum. Crop/PG/Duo samples and Jej/Ile samples were run on two separate gels, and one empty lane was included between two sets of A, B, C groups to avoid any contamination from one set of samples to another.

Figure 4

Comparative analyses of proteins identified in each digestive segment by proteomics. The total number of Gallus gallus proteins and Brassica napus proteins identified in each digestive content is presented in (a,b) respectively. Proteins (c, Gallus gallus, and d, Brassica napus), which were identified in at least two compartments (all A, B, C groups included) and those that were compartment-specific are shown in hatched and grey, respectively.

Figure 5

Radar diagram illustrating the kinetics of appearance/disappearance of proteases and other proteins along the digestive tract. This representation is extracted from supplementary dataset 1.

Figure 6

Diagram describing the experimental design and analyses performed on collected samples.