Semen traits of Hanoverian commercial stud stallions

In the present study, the semen quality traits gel-free volume, sperm concentration, total number of sperm, progressive motility and total number of motile sperm of 106 Hanoverian stallions of the National Stud Celle were investigated. In total 13.855 fresh semen reports of the years 2009 and 2010 were used for analysis. Mixed linear models were employed to estimate significance for the fixed effects of year, month, breeding station and age class of the stallion as well as the random effect of the stallion. The systematic effects of month, breeding station and age class of the stallion were significant for all semen traits. The year of semen collection showed significant influence on all semen traits but gel-free volume. Except for the sperm concentration the highest values for the semen traits were shown in the months June to August, the highest sperm concentration was in January to March. The random effect of the stallion accounted for 43 to 63% on the total variance of the semen traits. An extended model with the interactions of stallion by year, month and breeding station increased the relative proportions of stallion specific effects to 55-65 %. The interaction effects among stallion and year amounted to 6-14%, the interaction effects among stallion and breeding station to 8-15% and among stallion and month to 3-8%. In conclusion, semen quality is mainly determined by the stallion and in addition, significant interactions among stallions and environmental factors contribute to variations in semen traits.