What are the Risks?
In nature, inbreeding can cause some very deadly effects to individuals. It can decrease vigor, which is similar to the overall health of the animal. Body weight, fertility, and disease resistance can all suffer because of the effects inbreeding has. The same effects could be said for inbred rabbits as well, right? While it is true that highly inbred rabbits can have malformations, or misshaped parts, many of these malformations are lethal and the kit will either be stillborn or die shortly after birth (within a few days).
As stated before, malformations occur more frequently in highly inbred rabbits. But what is 'highly inbred'? In a laboratory setting, full sibling pairs have been mated for a number of generations (up to 20 generations in one line). Malformations begin to occur most commonly in the much later generations, normally around the 10th or 11th full sibling mating. They can range from cervical fusion (the backbone fusing together), an incomplete or very fragile skull, or scoliosis and deformations of the ribs (Chai and Degenhardt, 1962).
Other, genetic, issues can also occur much more frequently. The easiest example to see is malocclusion, or overgrown teeth, because while this issue is life threatening if not treated on a regular basis, it will not kill the kits before they mature. Other genetic issues may be present, but often inbred kits are few in number and die of other causes (such as malformations) before genetic issues can come to light.
Fertility rates can also be effected by intensive inbreeding. In Chai and Degenhardt's inbred lines, they noticed a decrease in kits per litter within the first several generations. However, the number of kits/litter did recover slightly in later generation matings. The rabbits they were working with were a medium sized breed (dutch x New Zealand) who averaged 7-9 kits/litter before inbreeding. They decreased to about 3-4 kits/litter within the first five generations of sibling mating.
In nature, inbreeding can cause some very deadly effects to individuals. It can decrease vigor, which is similar to the overall health of the animal. Body weight, fertility, and disease resistance can all suffer because of the effects inbreeding has. The same effects could be said for inbred rabbits as well, right? While it is true that highly inbred rabbits can have malformations, or misshaped parts, many of these malformations are lethal and the kit will either be stillborn or die shortly after birth (within a few days).
As stated before, malformations occur more frequently in highly inbred rabbits. But what is 'highly inbred'? In a laboratory setting, full sibling pairs have been mated for a number of generations (up to 20 generations in one line). Malformations begin to occur most commonly in the much later generations, normally around the 10th or 11th full sibling mating. They can range from cervical fusion (the backbone fusing together), an incomplete or very fragile skull, or scoliosis and deformations of the ribs (Chai and Degenhardt, 1962).
Other, genetic, issues can also occur much more frequently. The easiest example to see is malocclusion, or overgrown teeth, because while this issue is life threatening if not treated on a regular basis, it will not kill the kits before they mature. Other genetic issues may be present, but often inbred kits are few in number and die of other causes (such as malformations) before genetic issues can come to light.
Fertility rates can also be effected by intensive inbreeding. In Chai and Degenhardt's inbred lines, they noticed a decrease in kits per litter within the first several generations. However, the number of kits/litter did recover slightly in later generation matings. The rabbits they were working with were a medium sized breed (dutch x New Zealand) who averaged 7-9 kits/litter before inbreeding. They decreased to about 3-4 kits/litter within the first five generations of sibling mating.
The figure above (from Chai and Degenhardt, 1962) shows scoliosis and rib malformations in highly inbred rabbits.
References:
Chai, C.K. and Degenhardt, K.H. 1962. Developmental Anomalies in Inbred Rabbits. Journal of Heredity. 53(4): 174-182.