Genetic and environmental factors influencing gestation length and parturition conception interval in Hanoverian warmblood

The present study has the objectives to analyse effects influencing the gestation length (GL) and the parturition conception interval (PCI) in Hanoverian warmblood horses and subsequently to estimate heritabilities for the GL and the PCI. Data comprised artificial insemination records of the years 2008-2014 from the National State Stud Celle, Germany, and corresponding foaling data from the Hanoverian Breeding Society, Germany. A total of 19,315 seasonal records including 10,294 mares and 276 stallions were available for GL and 10,244 records for PCI with 5881 mares and 234 stallions. The average GL was 341.7±10.7 days. The fixed effects of the year and month of insemination, the age of the mare at the time of insemination, whether the mare had a foal with her from the previous season, the sex of the foal and the random effects of the mare and the stallion had a significant effect on the GL. For the effect of the month of insemination the GL was longest in the months of December to February and shortest in July and August. It was shortest in 2-4-year old mares and longest in mares >19 years. Also GLs were longer if the mare did not have a foal at foot from the previous season than in mares with a foal with her. Pregnancies with colts were longer than those with fillies. The average PCI was 38.1±25.9 days. Year and month of insemination, the age of the mare at the time of insemination and the mare as well as the stallion had a significant effect on the PCI. PCI was shortest in the months of December to February and increased until July and August. The PCI was longest in the youngest and the oldest age class of the mares. Heritabilities were estimated in linear animal models. A model including the maternal and paternal genetic effect resulted in heritabilities of 0.234 for the mare and 0.024 for the stallion for GL and 0.026 and 0.013 respectively for the PCI. Heritabilities for GL in a model including the maternal and direct genetic effects were 0.269 for the mare and 0.066 for the embryo. Mare-related effects seem to have the largest impact on GL, whereas environmental effects like a good post-parturition management highly influence the PCI.