Influence of the insemination regime on fertility traits in the population of Hanoverian Warmblood horses

The objective of this retrospective study was to figure out important factors on the fertility of mares and to optimize the management regime with regard to these factors. The analyses were based on records of the National State stud of Lower Saxony from 1997 to 1999, in total 16695 seasonal records which contain 33,664 heats. 127 stallions and 9431 mares were observed in the data. Traits analyzed were pregnancy rate and foaling rate with respect to the heat. The average pregnancy rate was 37.1% while the foaling rate was 32.6%. At the end of the breeding season 74.0% of the mares had become pregnant and in 64.7% of the cases a foaling was observed. Most of the factors included in the model had an influence on the fertility traits, except the age of the stallions. Next to factors, which can not be optimized by management like the year or the season within year, the number and the time interval between matings proved to be very important for fertility. To mate more often and in shorter intervals within a heat has resulted in higher fertility rates. The factors stallion and breeding history of mares had shown high influence. Reasons for the differences between stallions or between mares may be of environmental but also of genetical kind. Therefore it seems that breeding and selection can improve the fertility in horses.

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