Digestibility and availability of nutrients in feed ingredients

This chapter provides clarity for determination of values for digestibility by discussing different methods, terminologies, and specific considerations. It reviews digestibility and availability of amino acids (AA), carbohydrates, lipids, minerals, and vitamins. The ileal digesta contain undigested dietary AA along with endogenous AA that are secreted into the intestinal tract of pigs. The endogenous proteins mainly originate from mucoproteins, epithelial cells, digestive enzymes including gastric secretions, pancreatic juice, and bile acids, and serum albumin in forms of peptides, free AA, amines, and urea. Lipid digestibility in diets fed to pigs may be affected by several factors including lipid analysis, chemical and physical characteristics of fatty acids, dietary factors, and animal factors. Calcium in swine diets is mostly provided by limestone, dicalcium phosphate, and monocalcium phosphate because most grains and oilseed meals have low Ca concentration. Vitamins are essential nutrients that are required for normal metabolic function of the body.