The present invention includes methods for artificially inseminating animals using an improved artificial insemination device that prevents contaminants from entering the opening at the end of an insemination sheath during insertion through the reproductive tract of an animal. A thin protective cover or membrane is provided at the tip of the sheath to seal it, the membrane being designed to rupture under the pressure from the seminal fluid being applied by the plunger used to eject the semen from the insemination gun. The protective cover can be an integrated portion of the sheath itself, or a material applied to the tip of the sheath. The protective cover is minimal in size as to not increase the diameter of the artificial insemination device so that there is no loss in tactile sensitivity to the breeder who must maneuver the invention through the animal's reproductive tract.