The thing with fawns,regardless of any lethal genes is to breed young.If you wait til after 12 weeks you'll struggle to get pregnancies and will be very unlikely to have large litters or multiple litters from one doe.I think they are a variety that does well being left in with the buck. The lethal gene reduces litter size by 25 % but I don't have any problems breeding them.Youth is the key.Breed early and don't keep does after two litters,they rarely produce again.The tan outcross isn't essential for breeding,just improves type and produces winners for showing.