[Toxicity by relay. II. A method for the asessment of safety to human consumers of carbadox, a growth-promoting additive to the feed of slaughter pigs].

A toxicity by relay. II. A method for the assessment of safety to human consumers of carbadox, a growth-promoting additive to the feed of slaughter pigs. A new methodology called "toxicity by relay" has been used to assess the potential hazard to humans of incorporating an additive into animal feeds. This methodology considers a farm-reared animal as a "relay" between the food additive and the human consumer, and employs laboratory animals as "pseudo-consumers". These laboratory animals are fed throughout their entire lives with the meat or organs of the "relay" animals which have been reared on feeds supplemented with various levels of the additive. In the present study, the toxicity of carbadox was assessed in this way. In pigs, where it is used as a growth promoter, carbadox is metabolised into serveal different products, and so an assessment of its safety using traditional methods of studying the toxicity of a substance and tis known metabolites, would perhaps be subject to error. A safety factor for man, in relation to the safety factors for rats and dogs, was calculated using (a) the comparative consumption of the laboratory animals and man; (b) an assessment of the highest dosage likely to be consumed in normal circumstances compared to the laboratory dosage, and (c) the consideration that in the laboratory there is no period of withdrawal from feeding before sacrifice as is the case with animals for slaughter. Pigs were used as "relays" in the present study by supplementing their feed with carbadox. The meat and/or livers of these animals were then fed daily to (a) rats for a period of 3 generations; (b) rats for 24-25 months, and (c) dogs for 60 months. No abnormalities were observed at the termination of the experiments. We may therefore conclude that there is no hazard for the human consumer from the use of carbadox as a pig-feed additive.