(Photo: Flickr/David Masters)
Q: My rabbit (dwarf lop-eared breed) gave birth to 4 babies about a month ago. Two were slightly smaller, but one soon caught up to the others. The remaining small one was really energetic before, but now it's not responsive and has a faint clicking noise when it breathes. How can I help?
A: These rabbits (sometimes called Holland lops) are the breed that I raise. When dealing with dwarf rabbits, there is a dwarf gene involved. Each rabbit has 2 genes to determine size; it got one from each parent. We'll call the gene for normal size 'N' and the gene for the small size 'D.' Dwarf rabbits that grow up to be healthy adults have one of each gene, so ND.
If a rabbit gets the N gene from both parents, so it is NN, it will be larger, with a more pointed face, and longer ears. If it gets a D from each parent, so DD, it is in trouble. Such bunnies will be smaller than the others, and among show breeders are often referred to as "peanuts."
Because of how genetics works, when breeding dwarf rabbits, about one-fourth will be DD. Most of them die within the first week after birth. Once in a while, one lives to be 3 to 5 weeks, then the health problems associated with having the double D manifest, and they will die. It is especially sad then because they are at their very cutest.
Your little bunny is most likely a DD, or peanut. That clicking sound you hear indicates a breathing difficulty, probably pneumonia. Because of all the circumstances involved, it is highly unlikely that he will respond to any treatment, but if you wanted to do everything possible, you could take him to a vet.
However, in all my years of rabbit breeding, I've never seen one of these little ones survive to adulthood. I'm so sorry to give you such unpleasant news, but I feel you deserve an honest answer. Here is a link to read more about this condition.
-- Answer from Anna N., a biologist on JustAnswer.