Factors affecting the reproductive performance of Finnish trotter stallions

Acknowledgements: *Suomen Hippos, the Finnish Trotting and Breeding Association, generously provided their mating and pedigree databases for the purpose of this study Materials and methods The original data* consisted of all registered matings of FH and SB during the years 1991-2005 in Finland. There were 69205 cases (= one mare bred by one stallion per breeding season) altogether. Analyses were performed with SAS (proc freq and chi-square test), PEDIG-software (inbreeding coefficients), WSYS software (building a linear fixed effects model, analysis of variance), VCE6 program package (estimating the effects of random factors with a mixed model), and PEST program package (best linear unbiased estimates (BLUE) for fixed factors). Studied variable was foaling outcome, because it was considered more reliable than pregnancy outcome in this kind of data recording: 1 = a full term live or dead foal was born, and 0 = not pregnant, aborted or mare died during gestation Fixed factors in the models were month and year of mating, mating type (on-site insemination, transported semen, frozen semen, natural mating), age group of stallion, inbreeding level of the expected foal, and mare type (maiden, barren, rested or foaled) and age. Genetic components were included as random factors. Results The average foaling rates were 64.5 % for FH and 70.8 % for SB. The effects of all fixed factors were found to be statistically significant in the fixed effects model. The yearly foaling rates of both breeds exhibited a downward trend, which was more apparent for FH (Figure 1). Increasing stallion age (Figure 2) had a negative impact on fertility. Mating type (Figure 3) and inbreeding class of the expected foal (Figures 4 and 5) also affected foaling rates.