The Swedish Vallhund breed can be born either with a full tail or with a naturally shorter tail. The length of the shorter tail can range from almost a full tail, half a tail, a bob tail to no tail at all.
The gene for this natural short tail is called 'T-box transcription factor T gene (C189G)'. It is a simple dominant gene which means if a dog has 1 copy of the T gene it will have a shorter tail. Unlike the unknown recessive tailless gene in a few breeds the dominant T gene does not have the associated risk of spinal problems. However the T gene is known as a dominant lethal gene, this means that embryos which inherit two copies of the T gene are not viable and will normally be reabsorbed. There is however risk of these non-viable embryos growing and being carried to term how common this risk is I can't say, I have seen reports of one case in this breed and two cases in Corgis. But as full tails are accepted and bred from in this breed to avoid the risk of non-viable embryos completely a breeder can breed short tail dogs to full tail dogs. Doing this there will never be any risk of non-viable embryos as the puppies will only be able to inherit one copy of the T gene.
So due to the fact that one copy of the T gene will not cause any health problems the short tail trait of this breed does not pose the health risks that the recessive tailless trait can.
The gene for this natural short tail is called 'T-box transcription factor T gene (C189G)'. It is a simple dominant gene which means if a dog has 1 copy of the T gene it will have a shorter tail. Unlike the unknown recessive tailless gene in a few breeds the dominant T gene does not have the associated risk of spinal problems. However the T gene is known as a dominant lethal gene, this means that embryos which inherit two copies of the T gene are not viable and will normally be reabsorbed. There is however risk of these non-viable embryos growing and being carried to term how common this risk is I can't say, I have seen reports of one case in this breed and two cases in Corgis. But as full tails are accepted and bred from in this breed to avoid the risk of non-viable embryos completely a breeder can breed short tail dogs to full tail dogs. Doing this there will never be any risk of non-viable embryos as the puppies will only be able to inherit one copy of the T gene.
So due to the fact that one copy of the T gene will not cause any health problems the short tail trait of this breed does not pose the health risks that the recessive tailless trait can.