Abstract: A method of manufacturing and a raw material and its useage are disclosed for increasing the percentage of mammalian offspring of either sex. The process of use utilizes a male-specific antibody coupled to a solid-phase immunoabsorbent material to effect a separation of sex-determining spermatozoa derived from a semen suspension. The male-specific antibody selectively binds male-determining spermatozoa, while the female-determining spermatozoa remain not bound and are recoverable. A male specific antibody that is monospecific is prepared from male cells subjected to a multistep process which includes using said cells for the hyperimmunization of a female species and the preparation of an antiserum which is purified as to specificity by a multiplicity of absorptions against female cells. The antiserum is fractionated to yield male specific monospecific immunoglobulin which may be used to effect a separation of sex determining spermatozoa.