Combinations of Growth Promoters in Veal Calves: Consequences for Screening and Confirmation Methods

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Abstract
Summary: This study investigates the influence of low dosages of β‐agonists combined with other growth promoters on screening and confirmation methods in male veal calves. Five groups of four calves were treated for 6 weeks with combinations of low dosages of β‐agonists (βAG, clenbuterol, mabuterol and mapenterol, 0.4μg/kg each twice daily) in combination with 17β‐estradiol (E2, 5mg 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 weight 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 βAG animals and metaplasia in the E2 group. Some 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 comedication does not markedly affect the histological changes induced in the hormonal target tissues. For screening purposes histology of the prostate 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 corticosteroids and thyreostatics, respectively. Vacuolization in the prostate appeared no reliable indication for β‐agonists. Samples of urine, faeces, liver and eye (retina/choroid) were analysed for β‐agonists. E2 significanthy increased the levels of all β‐agonists in the liver and faeces, whereas DEX significantly reduced these levels. These observations show that additional medication with different groups of growth prómoters can markedly alter the excretion of β‐agonists and thus influence (regulatory) control.