Review of microbiological and biochemical effects of skatole on animal production

Skatole, a compound formed by the bacterial degradation of tryptophan, has harmful consequences for the beef and pork industries. Skatole causes acute bovine pulmonary edema and emphysema (ABPE) in cattle and is responsible for boar taint in pigs. Many ruminants are susceptible to ABPE, a disease in which skatole acts as a very selective pneumotoxin that causes the degeneration of certain lung tissues. Skatole passes through the rumen, is absorbed into the blood, and is then bioactivated by cytochrome p450s of the MFO (mixed-function oxidase) system or the PHS (prostaglandin H synthetase) system to form a toxic intermediate. Skatole also affects the production of serotonin and, in high concentrations, can hemolyze bovine erythrocytes. Pigs are not afflicted by skatole, but the off-odor (boar taint) given off by their meat on cooking is offensive to consumers. Skatole is produced in the intestine by bacterial degradation and absorbed into the blood. If it passes through the liver without being metabolized, it accumulates in adipose tissue, the liver and the kidneys. Several factors are known to influence skatole deposition rates in fat, but one of the most important is believed to be genetic. Skatole is also toxic to many microorganisms. It has a fairly broad bacteriostatic effect and is toxic to rumen ciliated protozoa and to Tetrahymena. The fermentation of tryptophan may produce various compounds, including indole, indoleacetic acid and 3-methylindole (skatole), and may be influenced by chemical factors and the physiological and psychological status of the host. The bacterium responsible for the production of skatole is Lactobacillus sp. strain 11201. It is not pathogenic and is an integral part of the normal intestinal flora. Skatole production is not a constitutive function of this bacterial strain. The enzyme responsible for skatole formation is not thought to be cytosolic; it may be bound to the cell wall, exist as an aggregate enzyme or be a particulate enzyme. Skatole acts as a non-competitive inhibitor of the enzyme responsible for its formation.