Heritability and Repeatability of Speed for 2- and 3-Year-old Standardbred Racehorses1

Abstract

Repeatabilities (t) and heritabilities (h2) of racing time were estimated from data on 7,206 2- and 3-yr-old Standardbred pacers and trotters competing in 1-mile (1.6 km) charted races at six tracks between 1975 and 1978. A total of 38,487 records representing 2,387 sire progeny groups were divided into subsets by gait, age and track. Initially, the designation "class of race" was recognized as a subjective categorization that reflected nonrandom assignments of horses to races. After extensive investigation, we concluded that racing times should be adjusted by linear regression for the time of the winning horse (defined at the "pace" of the race). Residual regression coefficients of time on pace ranged from .61 +/- .08 to .79 +/- .05 s/s and appeared to adequately account for the environmental effects of class. Repeatabilities of adjusted times ranged from .32 +/- .08 to .55 +/- .04 and heritabilities ranged from -.25 +/- .22 to .66 +/- .16. Overall estimates of t and h2 (pooled over gaits, ages and tracks) were .44 +/- .01 and .29 +/- .03, respectively. When data were not adjusted for pace, the sire, horse and error variance component estimates were inflated by environmental effects (pooled t = .62; pooled h2 = .36). Racing time adjusted for pace is recommended for use as a selection criterion in Standardbred horses.

Effects of Change of Body Weight on Racing Time in Thoroughbred Racehorses

“…The estimated heritability and repeatability for racing time were 0.237 and 0.525, respectively, which are quite similar to the results reported in the other studies (Hintz, 1980;Tolley, et al, 1983;Ojala et al, 1987;Buttram et al, 1988; lee and Park, 1996, Park and Lee, 1999), and the estimated heritability and repeatability for body weight were slightly different in genders (Table 4). The estimated heritability and repeatability for body weight from the overall data, shown in Table 3, were 0.612 and 0.914, which were somewhat higher than those from the report of Lee and Park (1996).…”

Genetic analysis of haematological and plasma biochemical parameters in the Spanish purebred horse exercised on a treadmill

“…But that performance is the result of a complex combination of conformational parameters, both physiological and behavioural, with a certain degree of genetic transmission (Giulotto, 2001). There are many studies on the correct way to obtain heritability in the horse in order to gauge its performance (Tolley et al, 1983;Ricard and Legarra, 2010). This paper used a multivariate repeatability animal model separating biochemical and haematological variables and including the stud of the animal as fixed effects, age as a linear covariable and permantent environmental effect of horse and the animal additive genetic effect as random effects.…”

Estimating maximum performance: effects of intraindividual variation

“…Statistically significant repeatability of locomotor performance has been demonstrated in numerous other species (e.g. Bennett, 1980;Bennett, 1987;Tolley et al, 1983;Huey and Hertz, 1984;Garland, 1985;Huey and Dunham, 1987;Jayne and Bennett, 1990;Austin and Shaffer, 1992;Reidy et al, 2000). Repeatability is considered to set the upper bound for heritability of quantitative traits, and therefore indicates the potential for traits to respond to directional selection (Falconer and Mackay, 1997) (but see Dohm, 2002;Nespolo and Franco, 2007).…”