Heritability of semen traits in German Warmblood stallions

• Semen traits from warmblood stallions regularly employed for artificial insemination show moderate heritability estimates.
• Estimated breeding values for semen traits open the breeder the option to select stallions with above average semen quality.
• The large inter-stallion variance underlines the great impact of the stallion on semen traits.
• A selection index may be best suited to improve semen quality in warmblood stallions.

The objectives of the present study were to evaluate genetic parameters for semen quality traits of 241 fertile German Warmblood stallions regularly employed in artificial insemination (AI). Stallions were owned by the National Studs Celle and Warendorf in Germany. Semen traits analyzed were gel-free volume, sperm concentration, total number of sperm, progressive motility and total number of progressively motile sperm. Semen protocols from a total of 63,972 ejaculates were collected between the years 2001 and 2014 for the present analysis. A multivariate linear animal model was employed for estimation of additive genetic and permanent environmental variances among stallions and breeding values (EBVs) for semen traits. Heritabilities estimated for all German Warmblood stallions were highest for gel-free volume (h2 = 0.28) and lowest for total number of progressively motile sperm (h2 = 0.13). The additive genetic correlation among gel-free volume and sperm concentration was highly negative (rg = −0.76). Average reliabilities of EBVs were at 0.37–0.68 for the 241 stallions with own records. The inter-stallion variance explained between 33 and 61% of the trait variance, underlining the major impact of the individual stallion on semen quality traits analyzed here. Recording of semen traits from stallions employed in AI may be recommended because EBVs achieve sufficient accuracies to improve semen quality in future generations. Due to favorable genetic correlations, sperm concentration, total number of sperm and total number of progressively motile sperm may be increased simultaneously.