Effect of a horse's month of birth on its future sport performance. II. Effect on annual earnings and annual earnings per start

Abstract

This study examines the effect of month of birth and its interactions with sex, age and year of performance for performance in flat races, jumping races (steeple-chases and hurdle races), trotting races, and equestrian competitions (jumping, eventing, dressage). The level of performance was evaluated by considering the logarithm of annual earnings and the logarithm of annual earnings per start in each discipline. Significant interactions were found between age and sex in all racing disciplines and in jumping. In some cases, a significant interaction also appeared between month of birth and sex. This was ignored in our previous study. Taking this factor into account, however, does not change the conclusions of this article very much, although it allows a greater precision of the estimates. For example, the decrease of the effect of month of birth with increasing age is only significant for racing disciplines. This finding supports the idea that the effect of month of birth in racing horses results mainly from real age differences between horses from the same 'administrative' age class. Any lingering effect in horses older than 4 years seems to be stable and of smaller magnitude. For these adult horses the effect of age differences in month is expected to tend to zero and performance differences according to the month of birth remaining at this stage could therefore result from a seasonal effect, stable during the life of the animal. (© Elsevier / Inra.).