The rancher should do test crosses between normal sized cattle and dwarf cattle in order to identity which normal cattle are heterozygotes. Heterozygous cattle will produce 50% dwarf, 50% normal offspring while homozygous normal cattle will produce only normal offspring. By identifying the heterozygotes and then eliminating them from the herd (along with the dwarf cattle), the rancher will rid the herd of the allele causing dwarfism.
