Study was conducted on egg laying productivity and egg fertility of Muscovy duck in conventional and biological breeding of the fowls. The higher biological degree in the breeding method has lead to signifi cantly higher values of all the studied characteristics: 4-week prolongation of the laying season, higher values in the laying peaks, greater egg weight (85.32 versus 78.36 g ***) and egg fertility (97.81 versus 96.18% *). Summer spells of hot weather and the
high laying capacity in the peak did not exert a negative effect on the egg weight and fertility in biological breeding of the layers.
