EFFECTS OF TRANSIENT PREPUBERTAL 6-N-PROPYL-2-THIOURACIL TREATMENT ONTESTIS DEVELOPMENT AND FUNCTION IN THE DOMESTIC-FOWL

It has been wed established that thyroid hormones play an important ro le in regulating the onset of puberty and reproductive function in bir ds. In mammals it has been shown that transient hypothyroidism induced with the reversible goitrogen 6-N-propyl-2-thiouracil (PTU) can resul t in tremendous increases in testis size and sperm production and that the timing of hypothyroidism must correspond to the period of Sertoli cell proliferation. As the period of Sertoli cell proliferation is no t precisely known in the fowl, an experiment was conducted to determin e whether chicken testes have a similar window of sensitivity to PTU t reatment. Broiler breeder male chicks (Peterson) were placed in floor pens at one day of age and reared according to the breeder's managemen t guide for the entire 28-wk duration (controls) or up to the point of dietary treatment with PTU (0.1% w:w) for 6 wk that began at 2-wk int ervals (2-8, 4-10, 6-12, 8-14, and 10-16 wk of age); after treatment, birds were returned to feed restriction and photostimulated at 20 wk o f age. Birds were bled and killed, and testes were collected at 4-wk i ntervals. At 28 wk, one testis was fixed for histological examination and one was immediately placed in liquid N-2 for sperm counts. Treatme nt with PTU from 6 to 12 wk of age resulted in a 96% increase in mean testis weight at 28 wk of age (treated 39.3 +/- 4.1 g per testis vs. c ontrol 20.0 +/- 1.6 g per testis). These testes exhibited normal morph ology and increased relative sperm production. Treatment with PTU from either 8 to 14 or 10 to 16 wk of age resulted in approximately a 35% increase in testis mass at 28 wk of age relative to the control value (27.2 +/- 2.0 g and 27.7 +/- 3.6 g vs. 20.0 +/- 1.6 g per testis, resp ectively). However, both of these groups clearly demonstrated precocio us puberty and abnormal spermatogenesis. These results suggest that ap propriately timed PTU treatment may result in permanent increases in t estis size and sperm production in the domestic fowl.