a1 Molecular Biology and Animal Physiology Department, Faculty of Agronomy, 13 Avenue Maréchal Juin, B-5030 Gembloux, Belgium
a2 Microbiology Department, Faculty of Agronomy, 6 Avenue Maréchal Juin, B-5030 Gembloux, Belgium
a3 Chemistry Department, Faculty of Agronomy, 2 Passage des Déportés, B-5030 Gembloux, Belgium
Growth-promoters are banned by the European Community, but different hormonal cocktails are still illegally used. This experiment was therefore conducted to evaluate the effects of one of the most currently used cocktails on some hormonal parameters and spermatogenesis in finishing bulls in an attempt to provide a suitable screening technique for their illegal use. Sixteen double-muscled Belgian White Blue finishing bulls (mean ivcight: 535 (s.d. 37) kg) were blocked into control (C; no. = 7) and treated (Dex; no. = 9) groups. Animals were treated i.m. with the hormonal preparation (dexamethasone isonicotinate and phosphate, chlormadinone acetate and ethinyl oestradiol) on day 0, day 15 and day 30. Animals were slaughtered on day 45. Three h before each treatment and just prior to slaughter, jugular blood samples were collected to monitor the testosterone (T) response to an i.v. injection of gonadotropin releasing hormone (GnRH) (0·5 fig GnRH per kg body weight). Testicular tissue was also collected at slaughter. Plasma T and insulin-like growth factor-1 (IGF-1) concentrations were measured by radioimmunoassay. IGF-binding proteins (IGFBPs) were evaluated using Western ligand blotting. Daily weight gains were lower in the control group (1·29 (s.d. 0·13) kg for C v. 1·60 (s.d. 0·39) kg for Dex) but the difference ivas not significant. After treatment, spermatogonia, spermatocytes, spermatids and spermatozoa disappeared from the testis and seminiferous tubules consisted only of Sertoli cells; these observations suggest that treated animals were sterile. Moreover, plasma T concentrations in response to GnRH stimulation were suppressed fP < 0·001) in the Dex group between day 15 and day 45 (mean maximal responses: 5·4 to 7·9 μg/l in C group v. < 0·2 μg/l in Dex group at day 15, 30 and 45). Treatment did not show any prominent effect on plasma IGF-1 levels but increased IGFBPS band intensity. In conclusion, treatment with a cocktail containing dexamethasone esters, chlormadinone acetate and ethinyl oestradiol for a short period induced a number of changes in finishing bulls luhich might be possible to develop as a screening method for the identification of illegally treated animals.
(Received November 08 1993)
(Accepted March 18 1994)