The addition of certain enzymes (exogenous enzymes) to modern chicken feed not only optimizes the digestibility of long-chain nutrient components in the feed ingredients but also reduces the effects of components that interfere with the digestion and/or absorption of nutrients in the chicken's digestive tract (anti-nutritive factors). This brief article provides a brief overview of the role of exogenous enzymes in the struggle to optimize the performance of modern chickens amidst the challenges of feed availability and quality.
Chicken Gastrointestinal Physiology
Before entering the glandular stomach, also known as the proventriculus, through the lower esophagus (lower esophagus), the feed consumed by the chicken is temporarily stored in the crop. The crop itself is a diverticulum (widening) of the esophagus that serves as the initial softening process for feed with drinking water, saliva rich in amylase enzymes, and supported by the activity of several commensal bacteria.
On the other hand, the proventriculus is the chicken's stomach, rich in glandular cells that produce gastric acid (HCl) and the enzyme pepsin. Because chickens naturally lack teeth in their oral cavity, after the feed undergoes acidification and initial enzymatic breakdown in the proventriculus, it undergoes mechanical grinding of the feed particles in the gizzard, or muscular stomach (Sturkie et al., 2015).
Fundamentally, the chicken's digestive process is similar to that of other monogastric animals. The liver secretes bile, which emulsifies the fat components of the feed, and pancreatic enzymes such as amylase, trypsinogen, pancreatic lipase, chemotrypsinogen, and procarboxypeptidase, convert the feed into chyme, which gradually leaves the duodenum and enters the jejunum.
Several other enzymes, both secreted by the epithelial cells of the small intestine and secondary metabolites of the digestive tract microbiome, such as maltase, isomaltase, sucrase, enterokinase, lipase, and peptidase, also play a significant and indispensable role in the final stages of chicken digestion (Oakley et al., 2014; Oakley and Kogut, 2016).
Chickens have a pair of caecal appendages (ceca), where the resident microbiome ferments feed waste and produces several short-chain fatty acids that can be used by the chicken as an energy source and for gut health.
