The present invention relates generally to a method of treatment and to an animal model for the identification of molecules and genetic sequences useful in method of treatment including inducing or reducing fertility of male animals. More particularly, the present invention contemplates a method for the treatment of infertility or a method of reducing fertility and even more particularly a method for modulating spermatogenesis in an animal or avian species. There is also provided an animal model comprising a mutation in at least one allele of bcl-w or in a gene associated with bcl-w. Such animals fail to undergo productive spermatogenesis and can be used to screen for therapeutic molecules including genetic sequences capable of inducing, enhancing or otherwise facilitating spermatogenesis in said animals as well as a model for molecules and genetic sequences which can induce infertility.