Analysis of factors influencing the performance of English Thoroughbred horses in the Czech Republic

Significance of important factors influencing one of the main parameters of performance in the English Thoroughbred, i.e. general handicap (GH), was d etermined. GH data from flat races of Thoroughbred horses in the Czechoslov ak Republic in 1968-1993 and in the Czech Republic in 1994-1996 were used f or analyses. Evaluations were carried out separately for each age category: GHs of two-year, three-year and four-year horses. Two linear models with m ixed effects were used. Model 1 comprised these factors: year of birth (rac ing season), sex, father, mother's GH and mother's age. All factors were fi xed except the factor father, it was considered as random. The factor fathe r was omitted from model 2, the other effects were the same as in model 1. An analysis to determine the significance of differences between effects wi thin factors was made by help of model 1. The factors father and mother's G H were significant in all age categories, the factor mother's age was insig nificant in all categories, and the factors year of birth and sex were sign ificant in two age categories every time. A variation-covariance analysis w as made by means of model 2 when means were estimated by the least-squares method (LSM) for the year of birth, sex, mother's GH and mother's age. GH v alues ranged from 55 to 64 kg in all three age categories between 1976 and 1988, but there was a steep fall of GH values beginning in 1989 and 1990 an d lasting to the end of observations in 1993; it was likely to be caused by a different handicapper. It was confirmed by the highly significant factor mother's GH that this information should be taken into account to estimate breeding value. Mother's age was insignificant in all age categories in mo del 1 while in model 2 it was significant in two-year horses only. A conclu sion can be drawn on the basis of model 1 with higher informative capacity that no adjustment to the factor mother's age is necessary, that means it n eed not be applied to estimate and/or predict breeding value.