REASONS FOR PERFORMING STUDY : The carrier prevalence of severe combined immunodeficiency (SCID), lavender foal syndrome (LFS) and cerebellar
abiotrophy (CA) in Arabian foals in South Africawas determined in order to quantify the potential impact of these conditions locally. Furthermore, the carrier
prevalence of SCID prior to and following the introduction of a genetic test was compared to evaluate the effect of testing in the population.
OBJECTIVES : To estimate the carrier prevalence of SCID, LFS and CA in registered purebred Arabians born in South Africa in the 2004/5 and 2009/10 foaling
seasons and compare the changes in prevalence in these disorders between the 2 groups of foals.
STUDY DESIGN : Cross-sectional survey.
METHODS : Samples were collected from individuals randomly selected from 2 populations of purebred Arabian foals born during the 2004/5 and 2009/10
foaling seasons. Genetic testing for SCID, LFS and CA was performed on DNA extracts using specific polymerase chain reactions, with the products being
analysed using fragment analysis on a genetic analyser.
RESULTS : The carrier prevalence of LFS and CA for the 2009/10 season was 11.7% (95% confidence interval [CI] 7.6–17.0%) and 5.1% (95% CI 2.5–9.1%),
respectively, with no statistically significant change in prevalence between the 2004/5 and 2009/10 foaling seasons. However, the carrier prevalence of SCID
was found to have decreased significantly from 6.4% (95% CI 4.8–8.3%) in the 2004/5 foals to 3.4% (95% CI 2.2–5.1%) in the 2009/10 foals (P = 0.009).
CONCLUSIONS: The results of this study indicate that genetic screening of Arabian horses for SCID may have played a role in significantly reducing the carrier
prevalence within the breeding population and thereby reducing the birth of clinically affected individuals. This study provides an indication of the positive
effect of genetic screening for specific conditions in horses.