Heat increment as affected by protein and amino acid nutrition

The activity of feeding and the metabolism caused by digestion and assimila tion of food increase an animal's heat production. This increased heat prod uction has been referred to as specific dynamic effect, specific dynamic ac tion or heat increment (HI). HI is much larger when protein is a source of energy than when carbohydrate or fat are the sources of energy. HI for prot ein is much greater when the animal's ambient temperature is high than when it is low. Metabolisable energy is used more efficiently, thus having less HI, for maintenance than for production. A suggested explanation is that h eat resulting from digestion and assimilation of food can substitute for th e heat production in fasting when food provides energy equal to, or less th an, maintenance requirements. When energy intake is large enough to support production, HI from anabolic processes becomes a waste product that cannot substitute for a fasting or maintenance function. The same rationale can b e applied to the observation that dietary protein has a greater HI when an animal is at high temperatures. At low temperatures protein would be used f or maintenance. At high temperatures the same amount of energy from protein would be enough to support production. As a result, HI of the protein woul d be increased at high temperatures. The high HI of protein or amino acids when at a high level in the diet can be at least partially explained. Prote in synthesis requires a large amount of energy. Some energy is required to excrete nitrogenous waste. In addition, dietary protein stimulates protein turnover. Research findings have suggested that HI should be lowered by dec reasing dietary protein. For non-ruminant animals this could be accomplishe d by discovering the essential amino acid requirements for an ideal protein . The ideal protein should result in a minimum HI. Research to date general ly fails to document improved feed efficiency as a result of feeding an ide al protein.