Document Type : Full paper (Original article)
Department of Animal Sciences, College of Agriculture, University of Shiraz, Shiraz, Iran
Effect of propylthiouracil (PTU)-induced hypothyroidism during the prepubertal period, at a dose of one
g per kg of the diet, on serum testosterone level and seminal characteristics of Fars indigenous chickens was
studied. PTU was fed between 7th to 13th weeks of age and semen was collected at weekly intervals, starting at 21st week of age and continued for seven weeks. The effect of PTU treatment on serum testosterone level and body weight was significant (P<0.05). The effect of age on all parameters, including body weight, semen volume, sperm motility, percentage of live sperm, sperm concentration, total number of live sperm, and serum testosterone and thyroxine (T4) levels was also significant (P<0.01). The interaction effect of PTU treatment and age on semen volume, sperm motility, and percentage of live sperm was not significant (P>0.05); but it was significant for body weight, sperm concentration, total number of live sperm, and serum testosterone and T4 levels (P<0.01). At weeks 11 and 13 of age, serum T4 concentration in PTU birds was significantly lower but serum testosterone level was higher than in the control group. Sperm concentration in PTU birds was generally higher than in the control group, although the differences between the two groups were significant at weeks 20, 23 and 24. The total number of live sperm produced by PTU birds at week 21 of age was about 60% of the control group (P<0.01). A positive correlation (P<0.01) was found between testosterone level and body weight (r = 0.54 and 0.36 for the control and PTU groups, respectively). A small but significant positive correlation was found between T4 levels and body weight in the PTU group (r = 0.23; P<0.01), but not in the control group (P>0.05). The correlation between testosterone and T4 levels was not significant. Transient prepubertal PTU-induced hypothyroidism resulted in an increase in sperm concentration and production at certain stages after treatment, but the effect did not seem to last for a long period. The potential for increased efficiency associated with raising smaller birds which pass a neonatal hypothyroidism and eat less feed and produce normal semen, may be economical.