Mating of related individuals produces an inbred progeny, with an inbreeding coefficient that is one-half the additive relationship between its parents. One of the consequences of inbreeding is reduction of the mean phenotypic value or inbreeding depression, particularly for reproductive and fitness characters. Another consequence of inbreeding is reduction in additive genetic variance within lines or increasing homozygosity and higher risk for the incidence of lethal or deleterious recessive alleles. In recent years many studies show that inbreeding reduces reproduction and fitness capacity, for example Inbreeding depression in reproductive and productive traits has been reported by Flock et al (1993), Smith et al (1998), Klemetsdal (1998), Thompson et al (2000a,b) and Nwagu et al (2007).

The purpose of this study was to investigation recent trends in inbreeding in Iranian Native Fowls and relationship between increase in inbreeding and decreases in economic traits including body weight, age at first egg, egg production and egg weight.