Properties of gizzard erosion-inducing substance in fish meal

Heated whole fish meal, produced from mackerel, was proved to induce gizzard erosion in broiler chicks by feeding for 6 days. The constituents of the water-soluble fraction of fish meal were suspected to be the cause of this lesion. Of them, histidine, histamine and nucleotides were examined. When added to milk casein and heated, histidine appeared to be the most toxic. It seemed, however, that histamine and IMP (inosine 5'-monophosphate) might be less toxic even when treated in the same way a histidine. Feeding of a large amount of histamine alone resulted in giving rise to a much disturbed profile of body weight gain, while a low incidence of gizzard erosion was observed in this case. Both heated fish meal and a heated mixture of casein and histidine were easily reduced in toxicity by acid hydrolysis. The latter was more sensitive to this treatment. On the contrary, papain had an action to diminish the toxicity of heated fish meal at all. Even after treated with papain, the heated casein-histidine mixture was still effective to induce gizzard erosion. These results might have come from different structural changes caused by heating of the two samples.