COMBINATIONS OF GROWTH PROMOTERS IN VEAL CALVES - CONSEQUENCES FOR SCREENING AND CONFIRMATION METHODS

This study investigates the influence of low dosages of beta-agonists combined with other growth promoters on screening and confirmation met hods in male veal calves. Five groups of four calves were treated for 6 weeks with combinations of low dosages of beta-agonists (beta AG, cl enbuterol, mabuterol and mapenterol, 0.4 mu g/kg each twice daily) in combination with 17 beta-estradiol (E2, 5 mg per animal per 14 days), methylthiouracil (MTU, 2.857 mg/kg bw twice daily) and dexamethasone ( DEX, 4 mg per animal per 10 days during the last 20 days of treatment) . Another group of four untreated animals served as controls. The weig ht and size of the thymus was reduced in the DEX group, the MTU group showed enlarged thyroids. Histologically the prostates showed vacuolar degeneration in the beta AG animals and metaplasia in the E2 group. S ome vacuolization was also observed in the controls. The testis.showed impaired development in all treatment groups, E2 leading to the most severe changes. DEX led to cortical atrophy of the thymus. MTU induced hyperplastic changes in the thyroid. These results indicate that come dication does not markedly affect the histological changes induced in the hormonal target tissues. For screening purposes histology of the p rostate can be used as a marker for oestrogens, whereas the weight of the thymus and thyroid can be used as an indication for the use of cor ticosteroids and thyreostatics, respectively. Vacuolization in the pro state appeared no reliable indication for beta-agonists. Samples of ur ine, faeces, liver and eye (retina/choroid) were analysed for beta-ago nists. E2 significantly increased the levels of all beta-agonists in t he liver and faeces, whereas DEX significantly reduced these levels. T hese observations show that additional medication with different group s of growth promoters can markedly alter the excretion of beta-agonist s and thus influence (regulatory) control.