Inbreeding in the Thoroughbred horse.

Changes in the inbreeding coefficient, F, in the Thoroughbred horse over the past 45 years have been investigated by genotyping 467 Thoroughbred horses (born between 1961 and 2006) using the Illumina Equine SNP50 bead chip, which comprises 54,602 SNPs uniformly distributed across the equine genome. The Spearman rank correlation coefficient, r, between the year of birth and F was estimated. The results indicate that inbreeding in Thoroughbreds has increased over the past 40 years, with r = 0.24, P < 0.001 demonstrating that there is a highly significant, though relatively weak correlation between the year of birth and inbreeding coefficients. Interestingly, the majority of the increase in inbreeding is post-1996 and coincides with the introduction of stallions covering larger numbers of mares.

Identification of the myostatin locus (MSTN) as having a major effect on optimum racing distance in the Thoroughbred horse in the USA.

One hundred and eighty-nine Thoroughbred horses that had won Graded Stakes races in North America were genotyped with the Illumina Equine SNP50 bead chip. Association tests using PLINK to determine whether any SNPs were associated with optimum racing distance (7 furlongs and under compared to 8-10 furlongs) identified a locus on ECA18 that was statistically significant (-log 10 EMP2=1.63) at the genome-wide level following permutation analysis (10,000 permutations). Bioinformatic analysis revealed that the two ECA18 SNPs with the highest statistical significance spanned the MSTN (myostatin) locus. Mutations in myostatin in several mammalian species have been associated with increased muscling, with a preferential increase in fast glycolytic type IIB fibres, which would increase power potential. Thoroughbred horses that race over sprint distances, which are 5-7 furlongs, are often characterized by impressive hind quarter musculature, strongly suggesting that the association observed between the ECA18 SNPs and optimum race distance is mediated through MSTN.

Effect of nasal occlusion on tracheal and pharyngeal pressures in horses.

OBJECTIVE: To compare tracheal and pharyngeal inspiratory and expiratory pressures achieved during 60 seconds of nasal occlusion in standing horses with pressures achieved in horses during intense exercise. ANIMALS: 5 Standardbreds. PROCEDURE: Tracheal and pharyngeal inspiratory and expiratory pressures were obtained from 5 horses during 60 seconds of nasal occlusion and compared with tracheal and pharyngeal pressures achieved during incremental treadmill exercise tests in which horses ran at 50, 75, and 100% of the speed that resulted in maximal heart rate (HRmax). RESULTS: Significant difference was not detected between peak tracheal inspiratory pressure during nasal occlusion and peak tracheal inspiratory pressure at HRmax Peak pharyngeal inspiratory pressure was significantly more negative, and peak tracheal and peak pharyngeal expiratory pressures were significantly more positive during 60 seconds of nasal occlusion than those observed in horses running at HRmax. CONCLUSION: During upper airway endoscopy in standing horses, 60-second nasal occlusion induced tracheal and pharyngeal inspiratory pressures that equaled or exceeded pressures achieved during high-intensity exercise. CLINICAL RELEVANCE: Nasal occlusion is useful to simulate upper airway pressures achieved during high-intensity exercise.