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Inbreeding Coefficients

As I research Welsh Ponies of Cob Type pedigrees I often see inbreeding Coefficients above what is considered optimal.

What is inbreeding and what are the consequences?

According to Dr. David W. Silversides at the University of Montreal : "When two animals that share common ancestors are bred together, a condition of inbreeding exists in the offspring. This inbreeding has two consequences for the phenotype of the offspring:

  1. Increased uniformity of “type”(i.e. phenotype) within the offspring, with increased “prepotency”, i.e. the ability of parents to transmit or fix a phenotype in the next generation. This uniformity of type is desirable to breeders.

  2. Inbreeding depression, which includes a reduction of vitality, reduced weight, reduced fertility, reduced rate of growth; increase rates of congenital anomalies, increased mortality, increased rates of recessive genetic diseases; a shortened life span. Inbreeding depression is cumulative: with increased inbreeding and over time there is an increase in inbreeding depression.

So, what is an inbreeding coefficient?

The inbreeding coefficient represents a numerical percentage, based on the analysis of a pedigree, that estimates the loss of genetic variation in an individual caused by the fact of having common ancestors on both the paternal and the maternal sides of the pedigree.

Here are some guidelines about inbreeding

General recommendations for breeding from Dr. David W. Silversides :

  1. Choose crosses that will reduce the inbreeding coefficient of the resulting offspring relative to the average for the breed (if this is available).

  2. If possible, avoid using an animal with common ancestors within its pedigree, at least not within the 3 to 4 most recent generations.

  3. Avoid incestuous breedings, with inbreeding coefficients of 12.5% and above.

  4. Keep inbreeding coefficients below 10%.

  5. Try to keep inbreeding coefficients below 5%.

  6. Think about sacrificing a bit of “type” for the sake of preserving the genomic health of your breed.

How can you find out the inbreeding coefficient of your Welsh Section C?

I joined All Breed Pedigree. Once you join you can click on "Reports" in the top left corner and either see what your pony's inbreeding coefficient is or make a hypothetical mating and see that proposed inbreeding coefficient. You can join from $10 for a month (plenty of time to run all your ponies through and print out the results) up to $50 for a year. You can also see inbreeding coefficients on Canadian Livestock Records if you have ponies that are Canadian Registered Welsh.

Our Section C Breeding Herd at Tegan Welsh

We have inbreeding coefficients that are generally around 3% for our stallions and a little higher for some of the mares. We do have one mare at 12% and it is not one that you would ever guess to be that high from reading her pedigree alone. Knowing these breeding coefficients helps us make breeding decisions especially when confronted with our limited genetic diversity among full Section C Welsh. I admit that I love Synod William, Synod Roy Rogers, Synod Roger and Nebo Bouncer in my pedigrees. But, I and my mad pony partners at Tegan Welsh also add in some super movement and super temperament / train-ability from other lines to make sure we keep our herd's genetic diversity at a healthy level. If you want to learn more I recommend Horse Genetics 4.0: Evolution, Breeds, Breeding Strategies and Inbreeding.

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