Some words about breeding

This text comes from Per-Erik Sundgren
doctor of agricultural sciences in pet genetics
and translated by Adriane DeWolfe

If on average you succeeded in holding the increase of inbreeding in the race under 0.5% per generation, the risk for unknown problems with hereditary diseases and defects could be held under control, and could even be reduced.  Roughly calculated, if the average inbreeding level of the offspring, calculated over 5 generations, is under 2.5%, then the strain is relatively well protected from future problems.  A groundrule is to never breed closer than cousins or the equivalent.  Pairing cousins increases the inbreeding level by 6.25%\.

If you succeed in creating a pairing which, calculated 5 generations back, gives an inbreeding level of zero for the offspring, then this should be regarded as very favourable.  If the race is generally healthy and you create such pairings, then no hereditary variation is lost and the race will, if all pairings fulfi these conditions, continue to be healthy.  There is no point in going further back in time when it applies to pedigrees.  For one thing, we can not do anything about what has already happened.  With individual pairings it is senseless to calculate long into the past, pedigrees become more unreliable the longer they are.  This is partially because not all animals are correctly recorded, and partially because inheritance occurs randomly.  This random inheritance of genes means that you can not know for certain that an animal a little further back in the pedigree in fact contributed genes to a particular offspring in every individual characteristic.  A highly d!
eveloped mammal such as the cat, has around 20-40,000 pairs of genes.  Even animals long back in the pedigree will contribute some of those genes to the future offspring - though only providing that the pedigree is correct.  Much of the discussion about cat breeding, however, revolves around the risk for the inheritance of individual defects or hereditary diseases.  In many cases they follow comparitively simple inheritance patterns, or in other words, they are controlled by few gene pairs.  In these cases, it becomes even more uncertain if a particular cat further back in the pedigree contributed any genes at all to those exact pairs of genes that cause the defect or disease.  With simple inheritance we even know with certainty that not all grandparents contribute genes to such a characteristic. It is therefore meaningless to eliminate breeding stock in the hunt for individual cases of such diseases a long ways back in a pedigree.  You will reduce the genetic variation !
Without having any certainty that it contributes to the reduction of the frequency of damaged genes.  The average relationship between animals is probably correct if all animals are correctly recorded in the pedigree, but for characteristics that are inherited through few gene pairs, such information about relationships can be misleading. Therefore, as a rule it is enough to concentrate on parents and grandparents, or at most one generation after that.  Breeding works like driving a car, it is admittedly a good idea to check the rearview mirror, but the most important thing is to direct your gaze forward in order to stay on the road. 
 

There is no such thing as a genetically flawless animal.  What we can do through breeding is to reduce the risk of damaged genes being doubled up together so that particular individuals suffer from genetic problems.  Through simple measures, such as never using sick or defective animals in breeding, never overusing a particular individual and seeing that there are enough individuals used for breeding to contribute to the next generations breeding stock, the strain is held automatically fresh.  Not only that, but the frequence of genetic diseases and defects will successively decrease, providing you can hold the future average inbreeding at a low level.  Animal strains in nature are held fresh for hundreds and thousands of years through such simple means.   It is only when the number of individuals sinks below critical levels that wild animal strains are also affected by the type of genetic damage that is so common among domestic animals since breeders go against fundamental! Conditions for how breeding can be conducted without harming the animals.

Within cat breeding there is also a small, unique problem.  It is not easy to keep unneutered males to a large enough extent to create the numbers needed for breeding.  A common solution for this problem is that breeders conciously collaborate with other breeders to reach a reasonable number of breeding males in each generation.  This would have much more favourable results for breeding than ambitious programs with extensive veterinary examinations of each particular individual used for breeding.  But it is of course often more difficult to achieve such collaborations than to individually pay high veterinary expenses. 

© Gentica

Kittens

  index