Zeranol and estradiol induce similar lesions in the testes and epididymides of the prepubertal beef bull.

Testes and epididymides of three groups (N = 4) of 6-month-old crossbred beef bulls implanted with a placebo or 150, 300, and 600 mg of estradiol-17 beta at birth, 2, and 4 months of age, respectively, or 36 mg of zeranol at birth only were examined for histologic changes and development. There was a reduction (p less than 0.01) in paired testicular weight and seminiferous tubular diameter (mean +/- SE) of zeranol- and estradiol-implanted bulls compared with control bulls, 29.0 +/- 1.3, 20.6 +/- 1.8 vs 48.1 +/- 5.9 g and 70.9 +/- 0.6, 73.7 +/- 1.2 vs 125.9 +/- 2.0 microns, respectively. The basement membranes of seminiferous tubules (mean +/- SE) were thicker in zeranol-implanted bulls (3.34 +/- 0.07 microns) than those in estradiol-implanted bulls (2.74 +/- 0.06 microns), both of which were thicker than those of control bulls (1.05 +/- 0.03 micron) (p less than 0.01). Supporting cells lining the basement membranes in zeranol- and estradiol-implanted bulls were predominantly undifferentiated whereas most supporting cells had differentiated into Sertoli cells in control bulls. Interstitial cells typical of adult Leydig cells and germinal cells in advanced stages of differentiation were abundant in control bulls, but scarce in both zeranol- and estradiol-implanted bulls. The epididymal epithelium was poorly differentiated, lacked microvilli, and was dysplastic, especially in the cauda epididymidis, in both zeranol- and estradiol-implanted bulls. The epithelium was lower in height (p less than 0.01) in both the caput and cauda epididymidis of treated animals than in that of controls.(ABSTRACT TRUNCATED AT 250 WORDS)