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Genetics of Racing Performance in the American Quarter Horse: IV. Evaluation Using a Reduced Animal Model with Repeated Records^{1, 2,}

Iowa State University, Ames 50010

Abstract

A reduced animal model that accounted for repeated records was developed to evaluate American Quarter Horses genetically for racing performance. The model defined a race contemporary group as a fixed effect and horse breeding value for racing performance and horse permanent environmental effects as random effects. Adjusted race finish time in seconds was the trait used as the performance record. All stallions, mares, geldings and non-parent horses were evaluated for racing performance at 320, 366 and 402 m. Phenotypic, genetic and environmental trends for racing performance were computed by using best linear unbiased estimates for race effects and BLUP for breeding values obtained as solutions from the genetic evaluation. Although breeding values were determined for horses born as early as 1938, the trends were presented for horses born between 1960 and 1983. The genetic trends for all three distances were negative (finish times were decreasing) at a rate of –.0088, –.0090 and –.0037 s per year for the distances of 320, 366 and 402 m, respectively.

¹ Journal paper no. J-12942 of the Iowa Agric. and Home Econ. Exp. Sta., Ames. Project no. 0155.

² The cooperation and financial assistance from the American Quarter Horse Association is gratefully acknowledged.

³ Dept. of Anim. Sci.

⁴ Present address: DeKalb Swine Breeders, Inc., DeKalb, IL 60115.

⁵ Computation Center.