Have you ever wondered how to go about selecting the right cats for your breeding program? Well, picking wanted traits will always remain a personal choice but perhaps we can provide some insight here on what you should steer clear from. The following outline expands on our experiences and the benefits of Burmese outcrossing and introduces using a pedigree as a means for determining ordinary from pragmatic.
When selecting any breeding pair you can choose from what’s right there in your back yard, what you might research and obtain from another breeder, and from wider ranging possibilities of selecting from overseas sources. Each approach has a path and each path will contain complexity. This selection process pretty much works no matter which path you choose.
Thanks to our myopic registries, our Burmese friends invariably form an exclusive pool. No matter how large our longstanding this pool has become – our national pool is by no means diverse. The resultant genetic loading can only represent the difference between our fittest genotype and the average fitness of our entire population. This diversity level has narrowed over time with the overall average diversity really only heading one way – down. This means our average fitness standing (overall health vigour and ability) can only remain stable or deteriorate. A decade ago one might have claimed our Burmese were holding their own. The evidence more recently; smaller litter sizes, increased neonatal death, increased rates of flat chests, higher frequency of genetic diseases or impaired immunity, suggests otherwise. This evidence is very much pointing to a deteriorating pool of genes.
Natural selection is the survival mechanism for any species and a primal reason for why our cats would get this right, if left to their own devices. Any individual cat will carry a loading of four or five genes which manifest as defects and are therefore susceptible to fatal disease or mutations. Generally, this level of genetic loading will not significantly affect an individual cat because the defects exist as a single allele, or form of gene. But if you heedlessly mate such a cat with its relatives, the odds for matches within those four or five alleles increases – as does the risk for disease or mutation. By analysing pedigrees you can defend against some of the obvious problems and so create your very own form of natural selection.
To further illustrate the demise arising from inbreeding, look no further than the kings of the Spanish Habsburg dynasty from the 1500s. The family line eventually disappeared but while it existed the dynasty was given to frequently venture into consanguineous unions. Their extended pedigree of 16 generations, involving around 3000 persons, shows an inbreeding coefficient moved strongly over the generations from 0.025 for King Phillip I, the founder, to 0.254 for Charles II. It has been determined that two distinct and separate disorders existed most likely the result of recessive alleles at unlinked loci. Although this illustration represents a historical conclusion, on what can only be described as a complex clinical profile, the death of Charles II at the age of 38 led to the extinction of the dynasty.
Coming back to our Burmese friends, it goes without saying that cats with desirable traits will continually be used to propagate such traits. Over time, genes upholding those traits will skew the gene pool and become more common. As will the equivalent four or five defective genes. The result can manifest as accelerated loss in alleles and increased problems showing up in progeny. Males are more susceptible because it only takes one gene on a chromosome A useful defence to such an outcome is to conduct meticulous analysis of pedigrees and adopt an unswerving discipline. So exactly how do you use a pedigree to stand up this defence?
There is no real way of knowing a defect exists with any cat unless a breeder opens up on a linked trait. The things to look out for are both predictable and logical. First up, note the name of catteries behind each Sire and Dam so as to determine if they have a reputation for producing high quality Burmese. DM is a title used that is associated with good breeding outcomes. Look for how many cats in the bloodline have this classification. Any preponderance of sires or dams within the generations needs careful consideration. If the cat is of low quality, obviously frequent appearances should be a cue to eliminate from further consideration. If the cat is of high quality, then proceed with caution based on what you intend to mate. Relatedness comes with desirable traits but it could also bring into existence mutation. Where possible, diversity will always de-risk your selection.
If a foundation population of Burmese cats produces a high rate of deleterious recessive genes you will find a response manifests as conditions propagating into progeny. The real, hard facts show the problem you will encounter is breeders cover up any conditions. Because so much effort, time and cost are invested into bloodlines, they would choose to see that investment continue and not be wasted. This means breeders will be entirely reluctant to openly discuss any problems which may present. For this reason any due diligence needs to come from you.
Some key points then. If most of the males show a condition, it will represent a dominant disorder, meaning that one of the parents has that disorder. If a 50/50 ratio of Sires or Dams shows a condition then an autosomal disorder exists. This means the condition manifests further back in the bloodline as a recessive disorder, and neither parent might show the condition. The more frequent the same cat appears within a pedigree the higher the risk for recessive genes to jeopardise your breeding program. Inbreeding is inbreeding. Whether is appears at generation 4 or commenced at generation 12, the fact remains you will take on the same risk. Look for catteries that encourage outcrossing and diversity because no matter how frequent, this simple contribution acts to mitigate risk of manifestation into conditions mentioned above. Pedigrees show up to 4 generations of bloodlines. The onus is on the consumer to research into earlier generations to confirm an acceptable risk exists based upon the above observations. After reading this passage it will become abundantly clear why Burmese breeding in Australia is not straight forward. Once you review even a few pedigrees you will soon find that conditions exist to confound sound selections. When looking for potential breeding options within Australia the opportunity to look internationally might just appear rosier.