Application of Synovex?H in veal calves: Steroid release and residues

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Abstract
Four experiments were carried out with veal calves which were implanted subcutaneously with Synovex‐H. Testosterone in blood plasma and also total oestrogens in plasma, urine and faeces during the trial and in liver, kidney and muscle after slaughter (62–75 days after implantation) were determined. Prepurification methods and radioimmunoassays for faeces and tissue samples were elaborated and validated. Variables between or within the trials were the sex, the dose (four pellets versus eight pellets; 25 mg testosterone propionate + 2.5 mg 17β‐oestradiol‐3‐benzoate per pellet) and the implantation site (either on the base of the ear or on the middle of the pinna). Results from the blood plasma and the excreta showed that using four pellets implanted in the middle of the pinna guaranteed a continuous release in order that oestrogen levels were maximally doubled in comparison to controls. On the other hand, application of the same dose at the base of the ear was characterized by an accentuated burst during the first three days (10‐fold elevation over controls). In plasma and excreta of male controls, higher oestrogen concentrations were measured as compared to the corresponding substrates of females. Comparing all groups, untreated males showed the highest testosterone levels. In all animals, residues of total oestrogens were of the same order of magnitude (kidney and liver 01–1.5 ng/g; muscle 0–32 pg/g) with somewhat higher means in the treated groups. Since all results are within the physiological scope, no risk for the consumer is visible after correct use of Synovex‐H.

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