Starch is the most abundant source of energy in broiler diets, providing about 50 % of apparent metabolisable energy. Broiler diets generally contain approximately 40 % starch, which is thought to be completely digested within the small intestine. However, the microbiota in the large intestine also plays an important role in starch digestion, producing volatile fatty acids that act as an energy source. The potential consequence of this is an incorrect prediction of the digestible energy values of diets when considering the contribution of starch. In this regard, it is important to understand the kinetics of starch digestion and the degree of disappearance throughout the chicken gastrointestinal tract.
The present study evaluated the effects of different diet types on starch digestion along the gastrointestinal tract of broiler. Birds were offered either a wheat- or corn-based diet, with 12 replicates of six birds per treatment, raised for 35 days. Titanium dioxide was added at 5 g/kg into all diets as an indirect marker to calculate digestibility. On day 35, excreta were collected and pooled per pen, and four birds per pen were randomly euthanized to collect digesta samples from the crop, gizzard, jejunum, ileum and caeca.
The quantity of undigested starch in the gizzard was lower in birds fed the wheat-based diet compared to those fed the corn-based diet. This suggests that the gastro-duodenal reflux of digesta was comparatively greater in the anterior tract of birds fed the corn-based diet. However, the undigested starch in the jejunum was lower in birds fed the corn-based diet, indicating that the likelihood of starch reaching the hind gut for microbial fermentation was greater in birds fed the wheat-based diet. The amount of undigested starch did not change from the ileum to caeca in both diets, demonstrating that starch digestion predominantly takes place in the distal jejunum, irrespective of diet type. There was no difference between the two diets with regards to the quantity of undigested starch present in the excreta.
Table 1 - Undigested starch (g/kg dry matter intake) along the gastrointestinal tract of broilers in response to feeding diets based on either corn or wheat.
In conclusion, the starch from the wheat-based diet was digested more slowly than that from the corn-based diet. Furthermore, it appears that a notable amount of starch from wheat was digested by microbial fermentation in the large intestine, while the majority of starch from corn was digested earlier in the tract, with very little digested after the jejunum.
ACKNOWLEDGEMENT: We would like to thank BASF SE for their support throughout this research.
Presented at the 30th Annual Australian Poultry Science Symposium 2020. For information on the next edition, click here.