Genetics and Health

When we got Beasley (in ‘97), we were aware that there was a genetic problem within the breed known as copper toxiosis (CT), our breeder assured us that the problem was not in her lines. Trusting, gullible fools were we. Beasley almost made 8, one of his litter brothers a bit beyond. The others we do not know.

Our understanding was, if we test for CT, and breed from only “clear” dogs, all will be well. That was the advice and assurance of established breeders at the time. Late ‘90’s, early ‘00’s.

Recent events, including our import of a “breeding” bitch from an assured breeder in the UK, with a heart murmur and other issues (of a genetic origin), has had us considering the possible impacts of a (probably), very limited gene pool here in Australia.

We are now developing a familiarity with new language, new ideas and developing our understanding of terms such as coefficient of inbreeding (COI), how to calculate it and why it is important. The average COI in the UK over the last 10 or so years for Bedlingtons, is 12, breeders (in the UK), regardless of breed, are encouraged to use dogs in their breeding program with a COI lower than the national average for that breed. The UK uses 10 generations to calculate COI. In doing a few COI’s on pedigrees we know (over 5 gens) COI’s have all been higher than the UK average.

Effective population size (EPS) is another indicator of genetic diversity. At lower than 100 a breed is considered to be critical, at less than 50, the breed is determined to be at risk of extinction. EPS in the UK is 48.3! With considerably less dogs in Australia it is highly likely that our EPS is significantly lower.

DNA profiling is another option that could be used to identify the loss of diversity among our breeding population. Variation across gene pairs (alleles) is an indicator of diversity. We have had profiles done for a number of our dogs (88 genetic “data” points) with heterozygous/different results on only 18 of the 88 at best. One result was only 7/88, less than 10%.

We believe that there is an urgent need to determine where Bedlingtons are in regards to health risks related to a lack of diversity beyond our established practice of DNA testing for CT.

We feel it is important to do what we can to ensure that we know what our COI’s are at a minimum. And to willingly share that information with others as a means of at least maintaining and, if possible, increasing genetic diversity, EPS, and reducing COI values to maintain and improve the health of our dogs.

A note on closing, a long term study of a different breed found that dogs with a COI of 6.25 or less were living, on average, 4 years longer than dogs of the same breed with a COI of 25 or more.

Same Same but Different

As per previous discussions I have been concerned regarding the limited gene pool in Bedlington Terriers in Australia for some time. Recently I have become interested in contributing factors such as Effective Population Size (EPS), Coefficient of Inbreeding (COI) and Loss of Genetic Diversity.

As mentioned in the previous post, Eric, our Swedish boy is heterozygous on 19/88 (21%). Missy from New Zealand, 14/88 (16%), Gemma 15/88 (17%), Raven 9/88 (10%) and the pups from Raven x Gemma 8 – 12/88 or (9 – 13%) heterozygous. This represents a loss of more than 50% of our genetic diversity (in some cases), across just two generations. Interestingly, the COI for this paring is only 2.15%, much lower than the COI (12 – 16+), I have calculated for a number of other people for mating purposes and the pups they have.

Some researchers have estimated the genetic diversity (heterozygosity) “between breeds” is around 27.5%. As expected, intra-breed percentages are much lower as a consequence of breeding for phenotype (same-same) without consideration for maintenance of genetic diversity (but different).

Loss of genetic diversity occurs through chance. Where two dogs heterozygous on the same DNA point, eg, A/T for both the sire and the dam, there is the potential for pups to inherit an A or a T from each parent. Possible combinations in this example are; A/A, T/T or A/T. If the pup inherits an A from both parents, then their result for that genetic trait becomes homozygous, the same if the pup inherits the T from both parents, ie, A/A or T/T (same same). It is only when the pup inherits an A from one and a T from the other that heterozygosity is maintained with a result of A/T (but different). Probability for this combination is 50% homozygous (A/A or T/T) and 50% heterozygous (combining an A from one parent and a T from the other).

Interestingly “same same” will result in “different”. Where both parents are homozygous on a trait but with difference, eg, A/A and T/T the result will be that all pups are now heterozygous for that trait, ie, must inherit an A from one parent and a T from the other resulting in an A/T heterozygous result. Heterozygosity can be increased where the breeding pair are known to be homozygous on the same trait but with different results as indicated above.

The pups from our recent litter have a “potential” for 19 heterozygous results. I will be submitting samples for the two pups I have yet to have DNA profiles done for but on “probability” alone I am not expecting better than 12 of the potential 19.

We may get lucky, but that is a bit like winning lotto, rarely going to happen.