To investigate the effect of dietary supplementation of sulfamethazine (SMZ) on growth performance, gonadal
development and hormonal changes, male and female Japanese quails (Coturnix japonica) were fed a control diet with or
without SMZ (0.2%) from one day post hatching until 6 weeks of age. In male quail, the deviation in growth performance
between SMZ and control chicks started at the 3rd week, and the disparity was significant at the 5th and 6th weeks. Hormonal
analysis revealed a substantial increase in the pituitary and circulating LH (at the 5th and 6th weeks), testicular and circulating
testosterone (at the 6th week) and plasma ir-inhibin (at 5th week) levels following feeding of the diet containing SMZ. The
testicular size and weights were significantly larger at the 5th week, and histological analysis demonstrated an enlargement
of seminiferous tubules, filling of the luminal fluid with spermatozoa and a number of interstitial cells. In female quail, the
body and ovarian weights were considerably increased at the 6th week. The SMZ supplemented group showed a significant
elevation in pituitary LH content (from the 4th week), plasma LH (at the 5th and 6th weeks), ir-inhibin (at the 3rd and 6th
week) and progesterone (at the 2nd, 5th and 6th weeks) as compared with control chicks. These results indicated that SMZ
was able to stimulate the secretion of gonadotropins and accordingly the gonadal hormones and that was associated with an
early gonadal function in male (at the 5th week) and female (at the 6th week) Japanese quail.