Generally, domestic cats have better immune systems than domestic dogs. I emphasise ‘generally’ because you have to drill down to individual animals (are they purebred or random bred, for instance?). I am referring to purebred dogs and cats and their proportion of the overal population. The proportion of purebred dogs in relation to the total population is much higher than for cats. The American Kennel Club recognises 195 dog breeds. The Cat Fanciers’ Association recognises 45 cat breeds.
The cat has excellent natural defences which are better than the dog’s because they been compromised much less than for the dog. This is because the dog has been domesticated for upwards of 40,000 years, although the scientists are unsure exactly when the first domestic dog existed. It is believed that the first domestic cats existed around 10,000 years ago but it may have been a little earlier.
The duration of domestication is important because it means that in a basic sense cats have not been subjected to selective breeding to the same extent as have dogs. And selective breeding undermines the animal’s defences to disease. It’s called inbreeding depression, a subject about which I have written and which you can read by clicking on this link. To be clear, selective breeding is inbreeding and it means paring together closely related animals. This is done to create a purity in the appearance of a cat or dog breed so the animal is to ‘type’ i.e, in line with the breed standard. The trade off is a decline in vigour or general weakness.
To quote Robinson’s Genetics, “loss of vigour is associated with the homozygosity of an increasing number of genes with harmful effects. Inbreeding exposes recessive genes which can be harmful to the health of the animal. To quote a cat breeder with a PhD, Heather Lorimer, “[Cat Breeders] must be careful not to “fix” immunodeficiency when we are trying to ‘fix’ type”. ‘Type’ means appearance in this context.
Among other things, inbreeding can result in a greater proneness to illness at any stage of development. The reason why dogs were domesticated well before cat is because they are more utilitarian. They are and were working dogs.
It’s actually more than just about when the cat and dog were domesticated. It’s about when selective breeding took place for the first time and for dogs selective breeding probably took place quite soon after the wolf was first domesticated. For cats we know that organised selective breeding of the domestic cat commenced around the middle of the 19th century i.e. from about 1850 onwards. This highlights the large difference between dogs and cats in terms of selective breeding.
And cats have been selectively bred for their appearance primarily and occasionally in conjunction with their character. Whereas dogs, as mentioned, were mainly bred for their working ability. Latterly it is for their appearance.
To add some more detail, there is an interesting article on the website: The Institute of Canine Biology. The author discusses the relationship between the immune system and inbreeding. They start out by saying the intricacies of a dog’s immune system depends on “exceptionally high diversity in the genes that run it”. The relative lack of genetic diversity in inbred dogs compromises the immune system.
The lack of genetic diversity also results in higher rates of autoimmune disorders. If an immune system does not turn all properly the animal is immuno-suppressed whereas if the immune system is over-sensitive or doesn’t turn off analogy auto-immune disease commences. Please comment if you have any queries and I will do my best to respond.
SOME MORE ON SELECTIVE BREEDING:
