Genetic analysis of conformation traits in Icelandic horses

lcelandic horses are popular riding horse in many countries. The official breeding goal accepted internationally aims for lcelandic horses with multi-riding ability and excellent temperament. Breeding evaluation is performed on eight conformation traits and nine riding ability traits. A Best Linear Unbiased Prediction method with a multivariate animal model is used to estimate breeding values (EBVs). The conformational traits should facilitate performance of gaits, a good head carriage and be aesthetically pleasing. Heritability estimates (h2) of conformation traits in lcelandic horses range from 0.22 to 0.46.
We performed a genome wide association study on the conformation traits: head; neck, withers and shoulders; back and croup; proportions and harmony; leg quality; mane and tail gracefulness; leg correctness and hooves. EBVs of 349 lcelandic horses (mainly from Sweden and the Netherlands) available in WorldFengur database and 33,577 SNPs (post quality control) were used in a mixed model method in the GenABEL package in R. A significant association of a SNP on chromosome 20 (p-value: 5.51x1ff7 ) and a borderline significant
association of a SNP on chromosome 4 (p-value: 8.60x10-6) were observed for the trait "head" (À= 1.01). Bonferroni significance level was 1.49x10-6• The breeding goal aims for a beautiful, delicate head; thin ears; large, open and alert eye; thin skin and fine hair; light jaws with straight nose profile and flared nostrils. Head is subjectively assessed and the heritability has been estimated at 0.33 in a previous study on lcelandic horses. The head size is one of the most important factors for the head assessment. In a study on Pantaneiro horses, the head size measurements have been shown to have moderate to high heritability
• (h2 is 0.55 for length and 0.27 for width). We also performed a genome wide association study on body length measurements for 64 lcelandic horses with 38,486 SNPs where a strong association (p-va/ue: 1.84x1ff5) to a SNP 113
on chromosome 1 (i\ = 1.01) was observed. The bonferroni significance level was 1.29x1ff6. The heritability for body length has been shown to be high (e.g. h2 is 0.72 in the Pantaneiro horse). Through preliminary results of this study we observed a genomic region significantly associated to head conformation and strongly associated to the body length in lcelandic horses. Further details on head conformation and body measures will be collected by a questionnaire and these phenotypic data will be subjected to a subsequent genome wide
association study.