| چکیده انگلیسی مقاله |
Introduction: Horses were breed for war, hunting, Transporting, recreational, and sports purposes (Khalili 2008). The criterion of selection is mainly based on the horse's own and their parents' performances rather than breeding value. Despite of relatively developed organization of horse husbandry in the country and availability of individual racing results for almost all the progeny and pedigree information of horses, the scientific methods are not applied in selection of the animals for improving the racing performance(Bakhtiari & Kashan 2009). Normally the criteria to estimate the racing performance are time traits (Langlois 1980, Tolley et al. 1985, Ekiz et al. 2005), handicap weights (Langlois 1980, Tolley et al. 1985), rank at finish (Chico 1994, Sobczynska and Lukaszewicz, 2003, Ekiz and Kocak 2005) and earning (Langlois 1980, Ekiz and Kocak 2005). Breeders have traditionally combined information from time trials and races with pedigree evaluations to select potential racing stock, but this evaluation has primarily been based on a subjective synthesis of available information. Although the Standardbred horse is extensively performance tested before selection of breeding stock, studies of the genetic and environmental factors that influence racing performance must be completed before specific selection criteria can be recommended to the industry (Tolley et al. 1983). Racing ability is the main selection criterion in race horses. Breeding value estimation for aspects of racing ability has been carried out following performance tests in many European countries(Àrnason et al. 1994). Traits such as rank, time, prize, etc. are used to estimate the genetic and phenotypic parameters of race horses(Sobczynska & Lukaszewicz 2004). Genetic parameters estimation of racing performance traits is important in breeding programs, therefore, appropriate methods should be used. This study aimed to estimate the genetic parameters of racing performance using a linear model in different breeds of Iranian race horses and estimation of their genetic and phenotypic trends. The result of this study would be used for designing a breeding program for Iranian race horses.
Material and methods: In this study, the performance records of Iranian horse breeds, including Thoroughbred, Crossbreed, Turkmen, and Arabian horse breeds from the horse racing club of the Iranian Equestrian Federation between 2006 to 2014 were used. Performance traits in this study include 1.Racing Time, 2.rank at the Finish, 3.Cumulative Earning, 4.Number of Places, and 5.Number of races. Data were collected and adjusted using Excel software and R scripts. The quality controls included outliers deletion and preparing records for statistical analysis. CFC software (Sargolzaei et al. 2006) was used to survey the structure of the pedigree. For fitting the appropriate model the significant effects were investigated and was applied by SAS software. Variance components and genetic parameters were estimated by the restricted maximum likelihood method for a single trait animal model using ASReml software. A genetic trend is a compilation of average EBV per generation and indicates the direction of change across generations. It is often visualized in a graph and is useful to check whether there are unexpected deviations from linearity, e.g. due to a selection limit. The genetic trend in the racing performance was estimated by calculating the linear regression of average breeding values within birth years on the birth year.
Results and discussion: The heritability of finish time at races for Crossbreed and Thoroughbred horses in 1000, +1500, and +1600 distances were estimated in the range of (0.19-0.29) and (0.36-0.45), respectively, and it was 0.25 and 0.13 respectively for the Arabian horse breed in 1000 and +1500 distance, and it was 0.35, 0.38, and 0.44, respectively for the Turkmen horse breed in 1000, 1550 and 1600 distance. The heritability of the rank was in the range of (0.046-0.17), (0.12-0.16), (0.24-0.28) 0), and (0.13-0.22) based on the linear model (Animal model), respectively for Crossbreed, Thoroughbred, Arabian, and Turkmen horse breed. The heritability of the cumulative earning was 0.20, 0.072, 0.019, and 0.033 respectively for the Crossbreed, Thoroughbred, Arabian, and Turkmen horse breeds. The repeatability of finish time for Crossbreed and Thoroughbred in 1000, +1500, and +1600 distance were estimated in the range of (0.38-0.59) and (0.40-0.52), respectively. Also, it was 0.64 and 0.54 respectively for the Arabian horse breed in 1000 and +1500 distance and were 0.60, 0.67, and 0.59, respectively for Turkmen horse breed in 1000, 1550 and 1600 distance meters. The repeatability of the rank was in the range of, (0.14-0.19), (0.13-0.17), (0.2-0.40), and (0.13-0.30), respectively for Crossbreed, Thoroughbred, Arabian, and Turkmen horse breed. The genetic trend of this trait for Crossbreed and Thoroughbred in 1000, +1500, and +1600 distances were estimated in the range of (-0.0629 to -0.0173) and (-0.0384 to -0.0236), respectively. Also, the genetic trend were 0.0372 and -0.0335 respectively for Arabian horse breed in 1000 and +1500 distance and were 0.0104, 0.587, and -0.0462, respectively for Turkmen horse breed in 1000, 1550, and 1600 distance. These results showed an inconsistency between this study and other research (references) due to the number of data, environmental and managerial factors such as the experience of horses in the race, and the type of equipment and tools involved in the competition. Regarding the low estimated heritability of some performance traits in this study, genetic progress through indirect selection will be more usefulness than direct selection on these traits. As the application of modern genetic selection methodologies continues to gain popularity in the racing industry, contemporary heritability estimates from the current population of Thoroughbred, Crossbreed, Turkmen, and Arabian horse breeds will play a vital role in identifying which traits are better suited to selection and in the development of more accurate genomic evaluations for racing performance. |