Abstracts / Journal of Equine Veterinary Science 31 (2011) 230-356242

[7] Poncet PA, Pfister W, Muntwyler J, Glowatzki-Mullis ML, Gaillard C.Analysis of pedigree and conformation data to explain genetic vari-ability of the horse breed Franches-Montagnes. J Anim Breed Genet2006;123:114-21.

Morphometric Traits in Gaited Breeds of Horse: PotentialFuture Targets for Mapping

E.A. Staiger 1, N.B. Sutter 2, R.R. Bellone 3, and S.A. Brooks 1

1Department of Animal Science, Cornell University, Ithaca, NY,USA, 2 Department of Clinical Sciences, Cornell University,Ithaca, NY, USA, 3 Department of Biology, University of Tampa,Tampa, FL, USA

Introduction: After initial domestication, the horse has beenselected by man primarily for transportation purposes. Early useswere for war and labor; however, thanks to the industrial revolution,present day uses are for sport and recreation, resulting in divergentskeletal size, conformation, and locomotion in thehorse.Sinceancienttimes, the horse has shown polymorphism in gait; at intermediatespeeds, the horse can perform a range of lateral and diagonal, 2-beator 4-beat gaits [1]. These are known as the trot and pace, and the rackandrunningwalk, respectively.While therehavebeenstudies intothemechanics of gait [2-4], there have been few studies that haveinvestigated how morphology influences gait in horses. The aim ofthis study is to present preliminary findings of morphological traitsthat may influence gait in horses. Quantification of thesemorphometric traits will be valuable in future studies to identifygenes associated with gait by whole genome association.Materials and Methods: The skeletal morphological assay waspreviously published in Brooks et al. [5]. The data gathered forthat study included, in part, 34 body measurements that spanthe head, neck, body, and limbs collected from 1550 horsesfrom 82 breeds, vital statistics (breed, age, sex etc) and ownerreported gait information. Horses were categorized as "gaited"if they were reported by their owner, or belong to a breed thatexclusively performs a gait other than trot at intermediatespeeds. The 34 measurements capture bone length andcircumference as quantitative variables. Statistical analyses wereconducted using JMP V8.0 software (SAS Institute Inc.).Results and Discussion: In our previously published study twoprinciple components of skeletal variation in the horse wereidentified, PC1 "size" (explains 62.6% of the variance) and PC2"thickness" (explains 5.4% of the variance) [5]. PC3 from thisstudy, although it accounted for a small 2.8% of the variancepercentage of the total variance across all breeds, wasstatistically different in gaited horse (P < .0001). The topcontributors to PC3 include the fore and hind pastern lengths,croup to dock length, ear length, and jaw width measures.To confirm differences in these measures specific to gait type the34 measures were normalized by withers height and comparedbetween the gaited (286 horses) and non-gaited categories (1264horses) using ANOVA. Nineteen measurements were found to bestatistically significant in gaited breeds. These included smallerjaw width (P < .0001), longer ear length (P < .0001), shorter dockheight (P < .0001), longer croup to dock length (P < .0001),smaller heart girth (P < .0001), shorter gaskin length (P ¼ .0333),smaller fore and hind cannon circumference (P < .0001), andsmaller fore and hind pastern circumference (P < .0001).Conclusion: Body conformation is a critically important trait innearly all horse breeds. It has been well documented thatconformation influences movement; hip and shoulder anglesinfluence the range of motion of the limbs, while limb segmentlengths influence shock absorption and strength of the limbs.Principal components analysis of measurements from a sampleof horses of different breeds has shown consistent trends inseveral quantified traits, including skeletal size (PC1) and shape(PC2). Studies are currently underway to map these PC-traits as

QTLs in the horse using the EquineSNP50 genotyping chip(Illumina INC). Although it seems likely that gait preference ishighly heritable, little previous work has documented thegenetic and biomechanical components to gait.This preliminary study, therefore, has several implicationsregarding the relative significance of individual traits in deter-mining a horse's quality of locomotion and predispositiontowards ambling or trotting. Whether by chance, or design, gaitedhorses have been selected for a unique set of conformationaltraits. These may influence gait performance. For example, longercroup to dock lengths might indicate a horse is more predisposedto running walk than rack or pace. Additional data, particularlyanalysis of horses in motion, may help to shed light on how theseindividual components influence gait type and quality.Identification of genes responsible for gait preference and gait-specific conformation in the horse, could inform studies oforthopedic disease susceptibility, and athletic performance, aswell as provide valuable tools to breeders selecting for gait.

References

[1] Harris SE. Horse gaits, balance, and movement. New York: HowellBook House; 1993.

[2] Nicodemus MC. Relationship between velocity and temporal variableof the flat shod running walk. Equine Veterinary Journal, supplement2002;34:340-3.

[3] Nicodemus MC, Clayton HM. Temporal variables of four-beat, step-ping gaits of gaited horses. Applied Animal Behavior Science 2003;80:133-42.

[4] Splan RK, Hunter HB. Temporal variables of the canter of theTennessee Walking Horse. Equine Comp. Exercise Phys 2004;1:41-4.

[5] Brooks SA, Makvandi-Nejad S, Chu E, Allen JJ, Streeter C, Gu E,McCleery B, Murphy BA, Bellone R, Sutter NB. Morphological varia-tion in the horse: defining complex traits of body size and shape.Animal Genetics 2010;41:159-65.

Tensile Strength of Tendons from Quarter Horses withHereditary Equine Regional Dermal Asthenia (HERDA)

J.E. Bowser 1, S. Elder 2, A.M. Rashmir-Raven 3,and C.E. Swiderski 11Mississippi State University College of Veterinary Medicine,Department of Clinical Sciences, Mississippi State, MS, USA,2Mississippi State University College of Agricultural and BiologicalEngineering, Mississippi State, MS, USA, 3Michigan StateUniversity College of Veterinary Medicine, East Lansing, MI, USA

Introduction: Hereditary equine regional dermal asthenia(HERDA)is an autosomal recessive connective tissue disorderaffecting Quarter Horse lineages [1-4]. HERDA has an estimatedallelic frequency of 28.3% within the cutting horse discipline [3].The HERDA phenotype includes loose, fragile, hyperextensibleskin that is easily injured and heals poorly [4]. Seromas,hematomas, and ulcerations are reported to occur primarilyalong the dorsum which progressively intensify in occurrenceand severity with age [1-4]. Despite individual variation indisease severity, the easily damaged skin, poor healing, andheritability of HERDA make affected horses unsuitable forriding or breeding. HERDA is currently diagnosed byidentifying the homozygous c.115G > A mutation in peptidyl-prolyl-cis-trans isomerase B, which codes for cylophilin B [4].However, the causal association between this mutation andthe HERDA phenotype has not been identified. Previously, wedemonstrated reductions in ultimate tensile strength (UTS),modulus of elasticity (MOE), and energy to failure (ETF) of skinfrom many corporal regions of HERDA animals [5]. Given thepresumed relationship between HERDA and abnormal collagenstructure, and the predominance of Type I collagen in skin, we