Genetic parameters for chronic progressive lymphedema in Belgian Draught Horses.

This research looks into the genetic parameters associated with Chronic Progressive Lymphedema (CPL) in Belgian Draught Horses. The study reveals that while several physical traits were associated with CPL, these markers were not sufficient to diagnose the disease, and suggests using the Estimated Breeding Values derived from repeated clinical examinations for more effective selective breeding.

Overview of the Study

• The research focuses on Chronic Progressive Lymphedema (CPL), a progressive and incurable disease that affects Belgian Draught Horses. The study seeks to identify genetic parameters associated with CPL.
• The study utilized a multitrait animal model approach, observing variables such as CPL clinical scores, skinfold thickness, and hair diameter from each horse.
• Due to uncertainty in diagnosing CPL in horses under three years old, the researchers created two data sets: a complete data set (D_full) and a restricted one (D_3+) that excluded records from younger horses.
• The research incorporated fixed variables such as age, gender, coat colour, and limb hair pigmentation, as well as random variables such as the permanent environment and date of recording.

Key Findings

• The research found that the certainty of CPL clinical diagnosis (CPLclin) increased when horses under three years were excluded (D_3+), increasing heritability coefficients and genetic correlations between traits.
• A significant proportion of CPLclin variance was attributed to permanent environmental effects in D_full, less so in D_3+.
• The date of the recording accounted for a proportion of variance ranging from 0.09 ± 0.03 to 0.61 ± 0.08.
• While there were additive genetic correlations between CPLclin, skinfold thickness, and hair diameter, these traits could not be used as a direct diagnostic aid for CPL.

Implications

• Despite certain physical traits being associated with CPL, the study found that these traits are not sufficient for diagnosis. This finding suggests that more direct methods, such as clinical examinations, might be necessary to effectively identify CPL in Belgian Draught Horses.
• Given the relatively low heritability of CPLclin, the research points towards focusing on Estimated Breeding Values derived from repeated clinical examinations for selective breeding, aiming to reduce CPL occurrence in the breed.