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Insect bite hypersensitivity (IBH) is the most common allergic skin disease in horses and is caused by bites of Culicoides spp. IBH reduces welfare of affected horses and at present no effective preventive measure or cure exists. Aim of our research was to increase knowledge of the genetic background of IBH in horse populations and to explore opportunities to reduce IBH prevalence through selection and breeding.
Data on Shetland pony and Friesian horse mares were gathered at obligatory inspections. IBH prevalence was 7.5% in Shetland pony mares and 18.2% in Friesian horse mares. Data were analyzed to identify risk factors. Combined effect of month and year of IBH scoring, region within the Netherlands and inspector were associated with IBH in both breeds. IBH prevalence significantly differed with coat colour and withers height category in Shetland pony mares. Moreover, prevalence was higher in Shetland pony mares with high body condition score (9.4%).
Quantitative genetic analyses revealed substantial genetic variation for IBH in both breeds. Heritability on the observed scale and on the underlying scale was 0.08 and 0.24 respectively in Shetland pony mares, 0.07 and 0.16 respectively in Friesian horse mares. Therefore, IBH is a heritable phenotype in both breeds. Repeatability was 0.30 in Shetland pony mares and 0.89 in Friesian horse mares. Maternal effect (0.17) was estimated in Friesian horse mares only.
To identify genomic regions contributing to the genetic variance, Shetland pony mares and Icelandic horses were selected according to a matched case-control design. Odds ratios of allele substitution effects of the unfavourable allele were between 1.94 and 5.95. Also, 13 and 28% of genetic variance was explained by all SNPs in respectively Shetland pony mares and Icelandic horses. Significant associated genomic regions across breeds suggest interesting candidate regions on ECA3, 7, 11, 20 and 23 contributing to genetic variance. Results support that ELA class II region on ECA20 is involved in IBH etiology, although follow-up studies are needed to confirm this and to identify genes in the other regions.
The general discussion explored possibilities to reduce IBH prevalence through breeding and discussed implications of using clinical symptoms or diagnostic test results. Simulated selection was based on EBV, which included own performance, progeny performance or genomic data. Selection on IBH clinical symptoms should be based on testing at least 10 but preferably more progeny, accompanying strict selection in sires to achieve reasonable genetic gain. Expected genetic gain per year in genomic selection outperformed other strategies, although implementation of genomic selection requires a considerable investment in a reference population. A diagnostic test for IBH (yet unfeasible to perform on a large sample) has the potential to increase genetic gain
|Qualification||Doctor of Philosophy|
|Award date||12 Dec 2012|
|Place of Publication||S.l.|
|Publication status||Published - 2012|
- animal breeding
- genetic analysis
- insect bites
- frisian (horse breed)
- shetland pony