Written by: Dr. Jacquie Jacob, University of Kentucky
Antinutritional factors are substances that when present in animal feed or water reduce the availability of one or more nutrients. It is important to have knowledge of antinutritional factors because they can adversely affect the health of your poultry flock.
Plants contain starch polysaccharides and non-starch polysaccharides (NSPs). A polysaccharide is a chain of sugar molecules (also known as monosaccharides) linked together. Polysaccharides are identified based on the carbon atoms of each sugar involved in the bond and the orientation of the hemiacetal oxygen atom (alpha/α or beta/ß). Some polysaccharides are antinutritional factors.
Starch is made up of glucose molecules connected together in what is referred to as an α-glycosidic link. In starch, the glucose molecules are connected by α-(1→4) linkages with a few α-(1→6) linkages. The α-(1→4) and α-(1→6) linkages in starch are easily broken by endogenous enzymes in birds and mammals. The α-(1→2) linkages between glucose and fructose in sucrose and the ß-(1→4) linkage between glucose and galactose in lactose also are easily broken during digestion. All other glycosidic bonds are resistant to endogenous digestive enzymes of animals. They can, however, be digested by microbe-derived enzymes.
NSPs contain sugars other than glucose and/or have linkages other than the α-(1→4) and α-(1→6) linkages common in sugar. An example of an NSP is cellulose. Like starch, cellulose is a chain of glucose molecules, but the molecules have ß-(1→4) linkages between them. The different orientation of the ß-links (compared to α-links) makes them resistant to digestion by endogenous digestive enzymes of animals. NSPs are part of plant cell walls and are closely associated with other polysaccharides or non-carbohydrate materials such as protein and lignin. These associations affect the behavior of the NSPs, especially with regard to solubility. NSPs generally are categorized as water-soluble or insoluble. Plants generally contain a mixture of both water-soluble and insoluble NSPs; the ratio of the two types changes with type and stage of maturity of the plant. Cellulose is insoluble in water and is considered fiber. Arabinoxylans and beta-glucans, two other NSPs, are partially soluble in water. Most NSPs adversely affect digestion in animals consuming them. Soluble NSPs affect the viscosity of the material in the digestive tract. This action, in turn, affects the ability of the digestive enzymes to reach their target. Absorption of any released nutrients is also reduced. This reduction in nutrient absorption results in reduced feed efficiency. The sticky nature of the digestive material also can result in the collection of sticky material around the vent of a chicken.
Common antinutritional factors include the following substances:
- Cyclopropenoid fatty acids
- Protease inhibitors