[Growth in broiler chickens after the regulation of sex differentiation using tamoxifen].

We studied the influence of an embryonal application of antiestrogen tamoxifen on gonad differentiation and sex dimorphism during the growth of Slovgal chickens. A single application of 500 micrograms tamoxifen to the incubated eggs before the onset of gonad differentiation induced in pullets the growth of the right gonad, which usually develops only in cockerels. Comparing the size of both gonads it is clear that the above dose of antiestrogen had the 22.31% masculinizing effect. Morphological changes observed just after hatching correlated with the testosterone concentration in plasma. The pullets masculinized by tamoxifen had a significantly higher level of male hormone. The changes in sex differentiation were reflected in the altered growth of pullet bodies. With respect to the higher growth rate and more effective feed conversion, their growth can be appreciated as masculinized. The higher body weight at the end of seven-week fattening (4.25% in comparison with the control group of pullets) was due to the higher trunk weight. The growth was stimulated by tamoxifen application also in cockerels (5.57% increase in body weight) but it was not accompanied by any changes in feed conversion.