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How disease affects nutrient requirements of pigs

During disease a metabolic alteration from anabolism to catabolism is considered essential for the success of the immune system response, as nutrients must be redistributed away from growth to the support of immune system functions to control the pathogenic infection. However, today there is very little quantitative data to enable nutritionists to formulate diets specifically for sick animals.

Immune system responses

It is widely understood that exposure to pathogens triggers the animal’s immune system, which in response releases a host of pro-inflammatory cytokines that modulate not only the immune response, but also, overall metabolism. Research has demonstrated clearly that activation of the immune system by these cytokines (even at subclinical levels) depresses appetite and reduces muscle protein synthesis, while increasing muscle protein degradation. Thus, the metabolic state of the diseased animal switches from anabolism (growth) to catabolism (muscle loss).

Naturally, when the immune system is activated, metabolism is directed towards the synthesis of immune system compounds. As it happens, nutrient requirements for these processes are quite different than requirements for normal growth. Today, there is a real lack of meaningful information regarding the nutrient requirements of diseased animals. All “standard” nutrient requirements have been traditionally derived from dose-titration experiments with relatively healthy pigs reared under near optimal conditions.
Amino acids

The immune system has its own unique set of amino acid requirements, which differ from that required for growth. For instance, acute-phase proteins produced by the liver in response to cytokines have a different amino acid composition than skeletal muscle proteins: the aromatic amino acids (phenylalanine, tyrosine, and tryptophan) are found in larger concentrations in acute phase proteins, which are produced in massive quantities in the liver at the onset of disease. It has actually been suggested that excessive muscle degradation is due to the differences in amino acid profile between muscle protein and acute phase proteins.

In addition, threonine is a major component of immunoglobulin-G and obviously higher dietary concentrations of threonine are required for antibody production than for body growth in pigs. Additionally, immunological stress causes an increase in amino acid maintenance needs as a proportion of total requirement. Overall, it appears that requirements for many amino acids may be increased in challenged pigs, whereas lysine requirements could be much lower.

You can read more about the necessary amount of minerals and vitamins in the diets for sick pigs in the full version of the article in the magazine “Profitable Pig Production” issue 1, 2013.

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