Biotransformation of Aflatoxin B1 and Its Relationship with the Differential Toxicological Response to Aflatoxin in Commercial Poultry Species

Aflatoxin B1 (AFB1) is a highly toxic compound (LD50 = 1-50 mg/kg) for most animal species, although it is extremely toxic (LD50 < 1 mg/kg) for some highly susceptible species such as pigs, dogs, cats, rainbow trouts, and ducklings. The toxic effects of AFB1 are both dose and time dependent and two distinct forms of aflatoxicosis, namely acute and chronic, can be distinguished depending on the level and length of time of aflatoxin exposure. In many species acute poisoning is characterized by an acute hepatotoxic disease that manifests itself with depression, anorexia, icterus, and hemorrhages. Histologic hepatic lesions include periportal necrosis associated with bile duct proliferation and oval cell hyperplasia. Chronic aflatoxicosis resulting from regular low-level dietary intake of aflatoxins causes unspecific signs such as reduced weight gain, reduced feed intake, and reduced feed conversion in pigs and poultry, and reduced milk yield in cows. Another effect of chronic exposure is aflatoxin-induced hepatocellular carcinoma, bile duct hyperplasia and hepatic steatosis (fatty liver). However, these effects are species-specific and not all animals exposed to aflatoxin develop liver cancer. For example, the only poultry species that develops hepatocellular carcinoma after AFB1 exposure is the duck. Differences in the susceptibility to acute and chronic AFB1 toxicosis have been observed among animals of different species. Animals having the highest sensitivity are the duckling, piglet, rabbit, dog and cat, while chickens, mice, hamsters, and chinchillas are relatively resistant. Further, mature animals are generally more resistant to AFB1 than young ones and females are more resistant than males. In general, in commercial poultry species, intake of feed contaminated with AFB1 results primarily in liver damage (the target organ of AFB1 is the liver), associated with immunosuppression, poor performance, and even mortality when the dietary levels are high enough. However, there is wide variability in specific species sensitivity to AFB1 and the susceptibility ranges from ducklings > turkey poults > goslings > pheasant chicks > quail chicks > chicks (Leeson et al., 1995). Even though there is still no clear explanation for this differential sensitivity, differences in susceptibility could be due to differences in AFB1 biotransformation pathways among species. The aim of the present chapter is to review the current knowledge on AFB1 biotransformation, with emphasis on