title: A reaction norm model approach to estimate the genetic effect of temperature on sportive performance of trotter horses.
abstract: The performance results of Spanish Trotter Horses were merged with the information from the nearest official weather stations, to estimate the effects of temperature (T) on speed during the day of the race. The resulting data set included: 104 125 individual results from 7653 races with 3772 participant horses and driven by 1402 jockeys. After a classical repeatability animal model in which the effects of T were assumed null, a total of five different random regression models (RRM) with the same fixed part were applied in a parsimonious nested process in which the (co)variance components for each random effect were estimated considering homo/heterogeneous responses across the trajectory of T during the race. The results demonstrate that performance is better when T increases from 4°C to 12°C, followed by a comfort zone (12-19°C) and a light but more stressful zone (>20°C). A significant change in the T during 20 years (+4°C) was observed whilst the speed of the race improved by +2.1 m/s during the same period. The information criterion (LogL, AIC and BIC) confirmed the existence of heterogeneity of (co)variance components along the trajectory of T scale. The model in which T effect was assumed non-constant across the T scale for animal genetic effects; the individual environmental permanent effects and the jockey effects fit the data better. Heritability had higher values (0.19-0.20) when T was <12°C and slightly decreases within the comfort and stressful zones. Genetic correlations were high and, as was expected, it decreases when difference between T increases. The best 150 animals for speed during the comfort zone were selected according to the Expected Breeding Value (EBV) estimated with the best RRM, and important variations were detected in the evolution of EBV across the trajectory of T. The presence of a genetic base related to T effect during the race in this type of performance is demonstrated.
authors.affiliation: Department of Agro-Forestry Sciences, ETSIA, University of Seville, Seville, Spain.
authors.forename: M Dolores
authors.initials: MD
authors.lastname: Gómez
authors.forename: A
authors.initials: A
authors.lastname: Menéndez-Buxadera
authors.forename: M
authors.initials: M
authors.lastname: Valera
authors.forename: A
authors.initials: A
authors.lastname: Molina
mesh_terms: D000818:Animals; D054874:Athletic Performance; D006736:Horses / Q000235:genetics*; D008957:Models, Genetic; D013696:Temperature
keywords: Breeding value; equine; genetic correlations; heritability