Nutrient digestibility in poultry

Practical Recommendations

• Regular analysis of all dietary components is recommended for a reliable nutrient profile of feed rations.
• To optimise the use of home-grown feed, the nutrient content of forage should be considered in diet formulation (Figure 1).
• High quality protein fulfils amino acid (AA) requirements, particularly lysine, cysteine and methionine.
• Diets formulated on digestible amino acids (DAA) are more effective than those formulated using total AA content.
• Digestibility of AAs is affected by dietary fibre content and the presence of anti-nutritional factors and protease inhibitors.
• Adding permitted enzymes to the diet can stimulate the digestibility of all nutrients, particularly protein and complex carbohydrates. They may also help birds to break down anti-nutritional feed components
• Starch (simple carbohydrates) is the primary energy source for poultry and is generally well digested.
• Complex carbohydrates in grains (wheat, barley, rye and oats) increase viscosity which negatively affects digestive processes and nutrient absorption.
• Fibre is poorly digested but helps to slow down the passage rate of other nutrients in the gut, improving digestion of all nutrients. A high intake of fibre can risk a reduction in total intake so restriction may be necessary.
• Fat digestibility is linked to the presence of other dietary components, and minerals in particular.
• Fat improves feed palatability and is required for energy and the absorption of fat-soluble vitamins A, D, E, and K.
• Age of bird influences fat digestibility with older birds being better able to digest fat than younger birds.
• As with fibre, fat can reduce feed passage rate (influenced by fat type and quantity) through the gut, enhancing digestion of all nutrients.
• Processing feeds can improve overall digestibility although finely milled feed reduces protein digestibility and pancreatic enzyme activity compared to coarser feed (Figure 2).
• Heat treatments can reduce anti-nutritional factors and, e.g., steam pelleting, can improve carbohydrate digestibility.