Associations between yearling body measurements and career racing performance in Thoroughbred racehorses

Population structure and genomic footprints of selection in five major Iranian horse breeds

The genetic structure and characteristics of Iranian native breeds are yet to be comprehensibly investigated and studied. Therefore, we employed genomic information of 364 Iranian native horses representing the Asil (n = 109), Caspian (n = 40), Dareshuri (n = 44), Kurdish (n = 95), and Turkoman (n = 76) breeds to reveal the genetic structure and characteristics. For these and 19 other horse breeds, principal component analysis, Bayesian model-based, Neighbor-Net, and bootstrap-based TreeMix approaches were applied to investigate and compare their genetic structure. Additionally, three haplotype-based methods including haplotype homozygosity pooled, integrated haplotype score, and number of segregating sites by length were applied to trace genomic footprints of selection of Asil, Caspian, Dareshuri, Kurdish, and Turkoman groups. Then, the Mahalanobis distance based on the negative-log₁₀ rank-based P-values was estimated based on the haplotype homozygosity pooled, integrated haplotype score, and number of segregating sites by length values. Asil, Caspian, Dareshuri, Kurdish, and Turkoman can be categorized into five different genetic clusters. Based on the top 1% of Mahalanobis distance based on the negative-log₁₀ rank-based P-values of SNPs, we identified 24 SNPs formerly reported to be associated with different traits and >100 genes undergoing selection pressures in Asil, Caspian, Dareshuri, Kurdish, and Turkoman. The detected QTL undergoing selection pressures were associated with withers height, equine metabolic syndrome, overall body size, insect bite hypersensitivity, guttural pouch tympany, white markings, Rhodococcus equi infection, jumping test score, alternate gaits, and body weight traits. Our findings will aid to have a better perspective of the genetic characteristics and population structure of Asil, Caspian, Dareshuri, Kurdish, and Turkoman horses as Iranian native horse breeds.

Body measurement of riding horses with a versatile tablet-type 3D scanning device

The measurement of various body dimensions of horses plays a significant role in quality improvement, genetic breeding, health, and soundness. There has been significant advancement in the technology for acquiring stereoscopic images with a three-dimensional (3D) scanner. This study aimed to validate the accuracy of body measurements obtained from stereoscopic images taken with a 3D scanner. We manually took the following body measurements for 8 riding horses: height at the withers, height at the back, height at the croup, chest depth, width of the chest, width of the croup, width of the waist, girth circumference, cannon circumference, and body length. Using a versatile tablet-type 3D scanning device, we captured a 3D image of each horse. Relative errors varied from −1.37% to 6.25%. The correlation coefficient between manual and 3D measurements was significant for all body measurements (P<0.01) except for width of the waist and cannon circumference. The low accuracy of cannon circumference (r=0.248) was due to effect of hair. A simple regression analysis of all body measurements revealed a strong correlation (P<0.001, R²=0.9994, root-mean-square error [RMSE]=1.522). Notable advantages of this methodology include high accuracy, good operability, non-contact, high versatility, and low cost. Further studies are required for the establishment of an accurate measurement methodology that can scan the whole body in a shorter time.

An Accurate Image Analysis Method for Estimating Body Measurements in Horses

This study proposes a standardized image analysis method for assessing horse conformation. A total of 34 adult American Quarter Horses (mean age = 6.7 ± 2.9 years, body weight = 489 ± 44 kg) were used. Reference angular measurements were performed using a digital goniometer, and reference linear measurements were determined using a standard measuring tape. For image analysis, photographs from the animal's left profile were taken at a distance of 3 m using eight markers to facilitate visualization. Images were processed using ImageJ software. Reference and estimated values showed great accuracy, with v² < 1%, Pearson's correlation coefficient > 0.999 (P < .001), and coefficient of variation < 2.70. Image analysis and reference results were similar (P > .05) for most variables. The highest coefficient of variation (3.05%) was observed for coxae-femur angle, where the software obtained an underestimation of 2.8° compared with the reference method. Body length resulted in an overestimation of 3.4 cm in relation to reference values, but coefficient of variation was low (1.54%). Discrepancies between estimated and reference results can be attributed to possible errors when collecting biometric data using portable measuring tools, angles and long measurements being more difficult to obtain. Software analysis of standardized horse photographs is an accurate and precise method for obtaining body measurements and is therefore recommended for future studies on horse conformation.

Prematurity and Dysmaturity Are Associated With Reduced Height and Shorter Distal Limb Length in Horses

The long-term effects of gestational immaturity in the premature (defined as < 320 days gestation) and dysmature (normal term but showing some signs of prematurity) foal have not been thoroughly investigated. Studies have reported that a high percentage of gestationally immature foals with related orthopedic issues such as incomplete ossification may fail to fulfill their intended athletic purpose, particularly in Thoroughbred racing. In humans, premature birth is associated with shorter stature at maturity and variations in anatomical ratios, linked to alterations in metabolism and timing of physeal closure in the long bones. We hypothesized that gestational immaturity in horses might similarly be associated with reduced height and different anatomical ratios at maturity. In this preliminary study, the skeletal ratios of horses with a history of gestational immaturity, identified through veterinary and breeder records, were compared with those of unaffected, closely related horses (i.e., sire, dam, sibling). External measurements were taken from conformation photographs of cases (n = 19) and related horses (n = 28), and these were then combined into indices to evaluate and compare metric properties of conformation. A principal component analysis showed that the first two principal components account for 43.8% of the total conformational variation of the horses' external features, separating horses with a rectangular conformation (body length > height at the withers), from those that are more square (body length = height at the withers). Varimax rotation of PC1 and analysis of different gestational groups showed a significant effect of gestational immaturity (P = .001), with the premature group being more affected than the dysmature group (P = .009, P = .012). Mean values for the four dominant indices showed that these groups have significantly lower distal limb to body length relationships than controls. The observed differences suggest that gestational immaturity may affect anatomical ratios at maturity, which, in combination with orthopedic issues arising from incomplete ossification, may have a further impact on long-term athletic potential.

Skeletal variation in Tennessee Walking Horses maps to the LCORL/NCAPG gene region

Conformation has long been a driving force in horse selection and breed creation as a predictor for performance. The Tennessee Walking Horse (TWH) ranges in size from 1.5 to 1.7 m and is often used as a trail, show, and pleasure horse. To investigate the contribution of genetics to body conformation in the TWH, we collected DNA samples, body measurements, and gait/training information from 282 individuals. We analyzed the 32 body measures with a principal component analysis. Principal component (PC)1 captured 28.5% of the trait variance, while PC2 comprised just 9.5% and PC3 6.4% of trait variance. All 32 measures correlated positively with PC1, indicating that PC1 describes overall body size. We genotyped 109 horses using the EquineSNP70 bead chip and marker association assessed the data using PC1 scores as a phenotype. Mixed-model linear analysis (EMMAX) revealed a well-documented candidate locus on ECA3 (raw P = 3.86 × 10(-9)) near the LCORL gene. A custom genotyping panel enabled fine-mapping of the PC1 body-size trait to the 3'-end of the LCORL gene (P = 7.09 × 10(-10)). This position differs from other reports suggesting single nucleotide polymorphisms (SNPs) upstream of the LCORL coding sequence regulate expression of the gene and, therefore, body size in horses. Fluorescent in situ hybridization analysis defined the position of a highly homologous 5 kb retrogene copy of LCORL (assigned to unplaced contigs of the EquCab 2.0 assembly) at ECA9 q12-q13. This is the first study to identify putative causative SNPs within the LCORL transcript itself, which are associated with skeletal size variation in horses.

Growth curves from birth to weaning for Thoroughbred foals raised on pasture

AIM

To mathematically describe the growth of a population of Thoroughbred foals reared on pasture in New Zealand from birth to weaning.

METHODS

Twice-monthly liveweight data (including birthweight; BW) from 218 foals (98 colts and 120 fillies) born over a 6-year period, and reared on four different pasture types, were available for analysis. Data truncated to the time of weaning (107-217 days old) provided 3,200 data points. After testing for non-linearity of the relationship of age and liveweight (LW), five non-linear regression equations were tested for goodness of fit.

RESULTS

Colts and fillies had similar BW, weaning ages, weaning weights (WW) and average daily gain (ADG) between birth and weaning (ADG b-w). Weaning age explained 48% (p<0.001) of the variation in WW and 11% (p<0.001) of the variation in ADGb-w. After correction for weaning age, BW explained 16% (p<0.001) of the variation in WW and 6% (p<0.001) of the variation in ADG b-w. The best fit of age and LW was the polynomial equations based on Akaike's information criteria (AIC), residual variance (RV), residual standard deviation (RSD), and coefficient of determination (R2). The most accurate, biologically sound representation of growth was provided by Brody's type equation: LW = [b0- (b0-BW) x e(-b1 x age)], and an equation including BW: LW = [((b0 x BW x age) + BWb1)b2], that was developed in this study (b0 is an intercept, b1 and b2 are regression coefficients, and e is the base of natural logarithms). The advantage of the Brody's equation is that ADG at a given LW can simply be calculated as: ADG (kg/day) = (b0 x b1)-b1 x LW.

CONCLUSIONS AND CLINICAL RELEVANCE

The similarity of the present data with growth data from the Northern Hemisphere provides further recognition that foals reared on pasture can grow as well as foals reared in grain-based systems in the Northern Hemisphere. BW provides a logical set point for the explanation of growth of the foal up to weaning, rather than the use of polynomial equations, which do not fully describe the biology of growth, even though they provide an accurate mathematical description.

Estimation of genetic parameters on conformation traits of the Iranian Arab horses population

Arab horse is a popular pure breed in Iran and is registered by World Arabian Horse Organization (WAHO). There is no scientific study and research about this breed. In this research 13 conformation traits on a random sample of the Iranian Arab horses studied. The estimate of variance components estimated by Animal Model and Derivative Free Restricted Maximum Likelihood (DF-REML) approach and DF-REML software. Heritability of conformation traits is also evaluated. The range of estimated heritability were (0.050 +/- 0.008) neck length and (0.614 +/- 0.087) croup height. Results indicated that, conformation traits were good traits for selection and horse genetic evaluation.