The effect of zearalenone on growth rate, organ weight and muscle fibre composition in growing rats.

The effect of prolonged zearalenone administered to growing rats on body and organ weight as well as on muscle fibre composition has been studied. Two muscles, M. longissimus dorsi and M. vastus lateralis, were selected for fibre analyses, and the different fibre types were identified by histochemical staining. Zearalenone caused retarded growth and reduced carcass weight in both sexes. With low daily doses female growth was retarded more than male growth, with higher doses the effect was the opposite. The most evident effects of zearalenone treatment on organ weight were enlargement of the liver in both sexes and of adrenal glands and the spleen in males. No effects were found on heart, kidney, testes or uterus. No significant changes of fibre number or diameter occurred in male rats after prolonged zearalenone feeding. In female rats, however, there was a 40% decrease in the number of alpha R fibres in vastus and a corresponding increase of alpha W fibres. Simultaneously the alpha R fibre size increased with 25%. No significant changes could be found in the activity of two enzymes in vastus, cytochrome oxidase and lactate dehydrogenase, as a consequence of the zearalenone treatment.