Physiology and Reproduction

Experiments were conducted to address recent reports of precocial testis development or testicular hypertrophy induced by the anti-thyroid agent 6-N-propyl-2-thiouracil (PTU) in domestic fowl and rodents. In three experiments, PTU was administered to male turkeys during different stages of development. The PTU was given in the feed at a concentration of either 0.1 or 0.5% and effects on thyroid hormones were measured. Periods of PTU treatment were 8 to 16 or 10 to 18 wk of age (Experiment 1); 0 to 8, 0 to 16, and 8 to 16 wk of age (Experiment 2); and 8 to 16 and 20 to 35 wk of age (Experiment 3). Data were collected to determine the effect of PTU treatment on testicular growth (weight), sexual maturation (semen onset and plasma testosterone concentrations), and early adult testicular function in terms of semen quantity (semen volume and sperm concentration) and quality (sperm viability and fertilizing ability). The 0.1% PTU treatment at 8 to 16 wk of age in Experiment 1 resulted in greater testis weights and sperm production than those of untreated controls at 24 wk of age. The difference was absent by 36 wk of age. Likewise, in Experiment 2, onset of semen production was advanced by about 2 wk by the 8 to 16 wk treatment as compared to untreated controls (23.3 vs 25.9 wk), although, at 32 and 36 wk of age neither the quantity nor quality of semen were significantly affected. Also in Experiment 2, 0.1% PTU treatment from 0 to 8 or 0 to 16 wk of age delayed the onset of semen production and depressed semen volumes at 32 and 36 wk of age without affecting semen quality. In Experiment 3, the mean age at the onset of semen was not significantly affected by 0.5% PTU treatment from 8 to 16 or 20 to 35 wk of age. In addition, semen volume and quality at 32 and 36 wk of age was similar to controls. It was concluded that antithyroid treatment with PTU was dependent on dose and time of treatment for effects on both sexual development and early reproductive performance. Precocial development and associated hypertrophy of the testes occurred but was transient. Thereafter, during initial reproductive function, semen quantity and quality were normal. (