Analys av dräktighets- och fölningsresultat inom svensk varmblodig ridhäst och svensk varmblodig travhäst åren 2000-2006

Abstract: The purpose of this thesis was to analyze conception and foaling results of Swedish warmblood and Standardbred trotters using breeding statistics during the years 2000-2006. Key issues in this thesis were: Have the conception and foaling results of stallions changed during the period 2000-2006? What is the effect of the use of various breeding methods? Is testicle size correlated with conception and foaling results? How important are age, breed and level of inbreeding of the stallion for conception and foaling results? Breeding statistics were available for 537 Swedish Warmblood stallions and 305 Standardbred trotter stallions. To be included in the analyses, a stallion must have mated at least ten mares in total over the period 2000-2006. This criterion was met by 313 Swedish Warmblood stallions and 272 Standardbred trotter stallions. Data on inbreeding coefficients were available for Standardbred trotters. The average inbreeding coefficients of the stallions in this study was 0.07. Breeding methods used were natural service and insemination with fresh, chilled, and frozen semen. During the study period, Swedish Warmblood stallions mated in total 33,983 mares and the Standardbred trotter stallions 38,485 mares. For the Swedish Warmblood stallions the insemination with chilled semen was the most common breeding method, approx. 60 percent, and for Standardbred trotter insemination with fresh semen was most common, approx. 50 percent. Age at mating varied between 3 and 30 years for Swedish Warmblood stallions, and between 4 and 30 years for Standardbred trotters (inseminations with frozen semen not included). The average conception and foaling results were 71.4 and 65.2 percent respectively for the Swedish Warmblood stallions, and for the Standardbred trotter stallions 74.8 and 67.2 percent, respectively. No statistically significant changes in conception and foaling results could be observed during the period 2000-2006. Logistic regression analysis was used to examine how breeding year, breeding method, age, breed, inbreeding and testicle size influenced conception and foaling results. All factors except testicle size had significant effect on gestation results, and all factors except breed and testicle size had significant effect on the foaling results. Increased inbreeding in the stallion led to a reduction in conception and foaling results. Stallions aged 5 to 12 years had the best conception and foaling results. Above this age span, higher age correlated with reduced results for the Swedish Warmblood. Repeatability was low, about 7 percent in the analysis of conception results and about 5 percent in the analysis of foaling results. No significant correlation between testicle measures on the one hand, and conception and foaling results on the other, was found in these data, when all mating methods were included. The width and volume of the right testicle showed a weak positive correlation to conception when only natural mating was included.