Abstract
BackgroundGiven that no influence of inbreeding on life expectancy could be demonstrated in Irish Wolfhounds in a previous study, it was decided to test the influence of inbreeding and other parameters on fertility in this breed.MethodsThe study was based on all Irish Wolfhound litters registered in Sweden between 1976 and 2007 (n = 822 litters) as provided by the Swedish Kennel Club (SKK) and combined with a pedigree database going back to 1862. Analyses were performed using linear regression in a Generalised Linear Model and other tests in the SAS system®.ResultsMean number of pups per litter was 6.01 ± 2.65, with a maximum of 13. There were no significant differences in either the number of litters or the number of pups between years of birth. Males were used for breeding at a significantly earlier age than females. Mean number of litters per parent was 2.96 ± 3.14 for males and 1.59 ± 0.87 for females. No influence of Wright's inbreeding coefficients over 5, 10, 20 and 30 generations and/or Meuwissen's inbreeding coefficients on litter size was detected. In the Generalised Linear Model, highly significant, but weak (coefficient of determination (R2) = 0.0341) influences were found for maternal age at mating as well as maternal inbreeding measured by Wright's inbreeding coefficient over 30 generations and Meuwissen's inbreeding coefficient. Paternal inbreeding coefficients over 5, 10, 20 and 30 generations and calculated after Meuwissen, as well as maternal inbreeding coefficients over 5, 10 and 20 generations did not have significant effects on litter size.ConclusionThe low coefficient of determination (R2) value of the Generalised Linear Model indicates that inbreeding does not have a strong influence on fertility in Irish Wolfhounds, which is consistent with earlier results and the breed's genetic history. These results likely reflect the aforementioned genetic history and should not be extrapolated to other breeds without prior breed-specific research.
Highlights
Given that no influence of inbreeding on life expectancy could be demonstrated in Irish Wolfhounds in a previous study, it was decided to test the influence of inbreeding and other parameters on fertility in this breed
Two models explaining inbreeding depression can be currently found in the literature: The partial dominance model, which states that the depression is due to recessive deleterious alleles that occur more frequently in a homozygous genotype in inbred populations, and the overdominance model, which states that the inbreedingassociated decrease in heterozygosity has a negative effect in itself even in the absence of deleterious alleles [6]
We considered the year of birth of the litters and the ages of both sire and dam at the time of mating, as well as dam parity and season as possible influences on litter size in our population
Summary
Given that no influence of inbreeding on life expectancy could be demonstrated in Irish Wolfhounds in a previous study, it was decided to test the influence of inbreeding and other parameters on fertility in this breed. Inbreeding is a major concern in purebred dog populations, and detrimental effects of inbreeding on fitness and the incidence of hereditary diseases have been demonstrated in several breeds Inbreeding depression in a population can only occur if allelic effects are not strictly additive – some degree of dominant-recessive interaction is necessary. Two models explaining inbreeding depression can be currently found in the literature: The partial dominance model, which states that the depression is due to recessive deleterious alleles that occur more frequently in a homozygous genotype in inbred populations, and the overdominance model, which states that the inbreedingassociated decrease in heterozygosity has a negative effect in itself even in the absence of deleterious alleles [6]. Current research seems to favour the partial dominance model, a contribution according to the overdominance model cannot be ruled out [7]
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