We investigated the effects of letrozole as a contraceptive on egg production and serum sex hormones in laying quails. Avian contraception is used for therapeutic reasons. Chronic egglaying, dystocia, salpingitis, prolapse of the cloaca or ovarian cysts are indications for the use of contraceptives. Medical therapeutic approaches as well as surgical contraceptive techniques are used to prevent continued ovarian activity and ovulation. One hundred 5-wk-old laying quail (Coturnix coturnix japonica) were randomly divided into five treatments, with five replicates of each treatment. Four quails were housed per cage as a replicate. The experimental treatments included control water, control multivitamin, 0.125, 0.25 and 0.5 mg/ml of letrozole. Egg production was significantly decreased in the letrozol groups, compared with the control groups. All quails receiving letrozole showed cessation of egg production only on the fourth day of treatment. A new productive cycle was observed on the 7-9th day of post- medical withdrawal in all letrozole groups and it reached a peak after 3 weeks. Mean estrogen concentration was significantly lower in the letrozole groups than in the control groups. Serum testosterone and progesterone concentrations were significantly higher in the treatment groups than in the control groups. Gross inspection of the birds revealed that the letrozole groups had a severely atrophied reproductive tract. Absence of yellow follicles was the common observation of letrozole groups. Administration of letrozole for 4 days causes cessation of egg production with regression of the reproductive tract and may be used as a contraceptive to prevent continued ovarian activity.
