Friday, November 7, 2014

Are We Breeding the Genetic Diversity Out of the Icelandic Horse?

From Wikipedia
Some recent research has indicated that perhaps there may be too much emphasis on breeding to only well known Icelandic stallions at the risk of losing the genetic diversity within the breed.  

Hreiðarsdóttir et al published a study "Analysis of the history and population structure of the 
Icelandic horse using pedigree data and DNA analyses" this year.  The genetics of this study is way over my head.


Problem to examine: "Breeding programs and the use of reproductive technology can increase the use of relatively few 'superior' individuals, usually select stallions, which in turn lowers the effective population." 

Historic Background: Horses were brought to  Iceland by the Norse settlers and no known import of new genetic material has happened since.  There was a genetic bottleneck when the eruption of Laki in 1784 to 1785 reduced the horse population to 8000 to 9000 individuals.  Sixty years later the population was up to 40,000.

Results:  Researchers found that horses from certain districts in Iceland remained relatively isolated in a genetic sense, horses in other areas were such as Skagafjörður were bred to more frequently, etc.  One chart shows how different districts contributed to the breeding in other districts.

"Inbreeding decreases as the pedigree is traced back suggesting a time dependent increase in population-wide inbreeding." Another chart shows how much total genetic contribution certain well know breeding horses have in the current population.  For example, Hrafn fra Holtsmuli contributes .106 (I believe that means he shows up in over 10 % of modern Icelandic horse pedigrees) in Icelandic bred horses.  The mare Síða from Sauðárkrókur is second on the list at .066.  Other influential stallions are, in order,  Orri from Þúfa, Ófeigur from Flugumýri, Fengur from Eiríksstaðir, Þáttur from Kirkjubær , etc.

Researchers conclude that "Inbreeding is on the rise, although that might partly be explained by an increase in pedigree completeness and lack of pedigree information in the early part of the 19th century."  Compered to other breeds, "The Icelandic horse has lower levels of genetic diversity and theta values than many much 
smaller breeds such as the Irish Draught (est. population size of 1000 individuals), Lusitano (6000 individuals), and Kerry Bog Pony (200 individuals)" but more genetic diversity than the Norwegian breeds such as the Fjord, Nordlund, Dale.  

Conclusion:  "Genetic diversity is the necessary fuel for a successful and sustainable breeding of any population and one of the goals of population management is therefore to maintain genetic diversity at a 
high level and inbreeding at a low level (Fernandez et al. 2005, Frankham et al. 2010). Genetic 
diversity is the necessary fuel for a successful and sustainable breeding of any population and one of the goals of population management is therefore to maintain genetic diversity at a high level and inbreeding at a low level 
(Fernandez et al. 2005, Frankham et al. 2010)."

No comments:

Post a Comment