A QTL for conformation of back and croup influences lateral gait quality in Icelandic horses

- A QTL for conformation of back and croup influences lateral gait quality in Icelandic horses.
- A complex interaction between the spine and the muscles of the back contribute to locomotion soundness, gait ability, and performance of riding and racehorses.
- The conformation of back and croup plays an important role on riding ability in Icelandic horses.
- associated with conformation of back and croup in Icelandic horses and to investigate their effects on riding ability..
- Haplotype analysis revealed two opposite haplotypes, which resulted in higher and lower scores of the back and croup, respectively (p-value <.
- Full list of author information is available at the end of the article.
- Conclusions: Our results show that the detected QTL for conformation of back and croup is of importance for quality of lateral gaits in Icelandic horses.
- The most important fea- tures for gait ability in Icelandic horses are the height of the horse at front compared to hind (uphill conform- ation) with well-balanced backline, croup proportions and width of chest [1, 3].
- Conformation of the back and croup thus play a major role on riding ability in Icelandic horses..
- These genes, along with other genes such as ZFAT and LASP1, affect not only the body size of the horse but more specifically the height at withers .
- Three novel missense variants located in the ADAMTS17, OSTN and GH1 genes explained 61% of the variance of.
- Therefore, the aim of this study was to identify genomic regions associated with conformation of back and croup in Icelandic horses and investigate their effects on riding ability traits assessed at breeding field tests..
- Genome-wide association analysis for conformation of back and croup.
- A summary of the GWA results for the 50 top SNPs is presented in Additional file 1..
- Phenotype association of the haplotypes with a significant effect on the score of back and croup.
- The two haplotype groups also differed significantly in means for the zoometric mea- surements of depth at breast, width of hips and thigh bones, and length of the forelimbs.
- Comparing allele frequencies of the top SNP identified from GWA analysis between different breeds revealed a higher frequency of the alternate allele (the favorable.
- 1 GWA results for the score of back and croup.
- Table 1 Results from haplotype analysis for the score of back and croup.
- coefficient, estimated effect of the haplotype on the score of back and croup from the glm model in the haplotype analysis.
- Functional annotation of genes in the region associated with the score of back and croup.
- None of the significant SNPs (on ECA12 and 22) overlapped any known QTL for conformation in horses [39]..
- Conformation of the back and croup plays an important role for riding ability, gait ability, welfare, and longevity of the horse .
- The present study was performed to identify genomic regions associated with conformation of the back and croup in Icelandic horses and investigate their effects on riding ability.
- Scoliosis is defined as a lateral curvature of the spine and it is the most common.
- Symptoms of scoliosis in horses has been described as an S-shaped bend of the caudal thoracic vertebral column, resulting in restricted movements of the hind limbs and inflexibil- ity of the back [51].
- Another report described symptoms as a lateral deviation of the head and cervical and cranial thoracic vertebral column to one side, and associated ro- tation of the thoracic vertebrae.
- However, severe thoracic vertebral malformations in horses are infrequent, and mild to moderate forms of scoliosis may go undetected as the strong dorsal spinal musculature can mask subtle deviations of the vertebral column [52].
- In general, disorders of the back appear to be relatively common in horses and lead to pain and decreased per- formance [51].
- Back and croup lt.
- Width of the hips (M7) b .
- The effect of the QTL is more likely related to functional advantage or disadvan- tage for movements and strength of the back and croup in horses rather than the result of more severe dysfunc- tions and pain.
- This is supported by the relatively high frequency of the unfavorable haplotype among the Ice- landic horses in the present study..
- Icelandic horses had a higher frequency of the alternate allele (the favorable allele) of the top SNP for back and croup compared with all other investigated breeds, in- cluding the other gaited and partly gaited breeds.
- Therefore, it is likely that the quality of the lateral gaits rather than the ability to perform the gaits is affected by the QTL.
- carry at least one copy of the mutant allele A in the DMRT3 gene known as the “Gait Keeper” mutation [30, 34].
- The Ice- landic horses in the present study had a high frequency of the DMRT3 “Gait Keeper” mutation of the 177 horses were homozygous AA.
- The other ge- notyped gaited breeds American Curly, American Saddle- bred and Morgan horses have a moderate high frequency of the DMRT3 “Gait Keeper” mutation .
- Trotters are also known to Table 3 Allele frequency of top SNP for back and croup and DMRT3.
- Top SNP the top SNP identified from the GWA analysis for back and croup AF alt frequency of alternate allele.
- DMRT3 AF alt allele frequency of the alternate allele A in the DMRT3 gene known as the “Gait Keeper” mutation.
- perform lateral gaits, and the reported frequency of the DMRT3 mutation is high in Standardbreds and relatively high in Coldblooded trotters .
- All of these gaited and partly gaited breeds had a higher fre- quency of the reference allele than the alternate allele for the top SNP of back and croup.
- The allele frequency of the top SNP did not differ between these two groups.
- How- ever, like all the other genotyped breeds, this group had a lower frequency of the alternate allele of the top SNP for back and croup compared to the Icelandic horses.
- None of the other genotyped breeds in this study segregates for the DMRT3 mutation [30, 34], nor do they perform lateral gaits..
- The 49 unassessed Icelandic horses had a similar allele frequency of the top SNP for back and croup as well as for the DMRT3 mutation as the 177 assessed Icelandic horses included in the present study.
- It is likely that there has been selection for the alternate al- lele of the top SNP in Icelandic horses..
- This may be explained, at least to some extent, by the effects of the genes ANKRD60 and LOC100056167.
- It is possible that a downhill inclination creates an imbalance between the front and back of the horse, causing diffi- culties for the horse to stretch the hind legs forward, thus losing the ability for self-carriage and collection..
- Length and form of the croup are also known to dis- criminate between high-class and low-class Icelandic horses [3].
- This trait is defined as how evenly the croup is shaped and suggests that the haplo- type does not influence the length or inclination of the croup, but only the shape of it.
- Complexity of the phenotype.
- Until around year 2010, a soft, lower backline was con- sidered to be favorable for the assessment of back and croup of Icelandic horses, as a low position of the back was assumed desirable for tölt [12].
- Horses with the haplotype associated with lower score of back and croup were more inclined to have a forward sloping and/or swayback backline..
- This study provides valuable information about the gen- etics of conformation of the back and croup in Icelandic horses.
- A novel QTL for the trait back and croup was detected on ECA .
- The QTL is associated with the back inclination, the form of the croup, and length of limbs as well as the quality of the lateral gaits pace and tölt.
- Only pri- vately owned horses participated in the study and the horses were not specifically selected based on conform- ation of back and croup.
- analysis consisted of the subjectively assessed score for back and croup recorded at breeding field tests between 1999 and 2018.
- Of the 177 horses had 115 attended more than one breeding field test.
- Back and croup.
- Assessment of the trait back and croup comprises several aspects of the conformation of the back, croup and loins.
- The slope and shape of the back- line, which is defined as the line from the base of withers to the lumbosacral joint, were assessed.
- Length and slope of the croup were also assessed, as well as the width and muscularity of the back, the length and width of the loins and the form and muscularity of the croup [12].
- A high score for back and croup represents a strong, well-balanced backline and a well-muscled wide back.
- When the judging panel has reached a consensus on a score for back and croup according to the judging scale, they have the pos- sibility to use standardized marks to describe the most prominent positive and/or negative attributes of the trait..
- The distribution of the scores for back and croup was slightly negatively skewed (coeffi- cient of skewness − 0.36).
- Transformation of the raw data to increase normality was tested but was found to not affect the results.
- Sub-traits based on standardized marks for back and croup For the purpose of more detailed analysis of the score for back and croup, the standardized marks used to de- scribe prominent positive and negative attributes of the trait were defined as two different sub-traits.
- backline and croup type.
- These sub-traits were analysed on a lin- ear scale ranging from 1 to 3, where 1 represented a positive mark, 3 represented a negative mark and 2 rep- resented no mark and was interpreted as an intermediate description of the trait (not positive or negative).
- 2 Examples of Icelandic horses representing high and low score of back and croup.
- Icelandic horse that represents high score of back and croup.
- Icelandic horse that represents a low score of back and croup with a forward sloping backline and a less muscled croup.
- 3 Distribution of scores for back and croup in the 177 horses.
- Scores of all these traits were included to in- vestigate the effects of the detected regions from GWA analysis on the trait back and croup..
- All these measurements were included to investigate the effects of the detected genomic regions from GWA analysis for the trait back and croup.
- Length of forelimbs is traditionally assessed from calculation of the differ- ence between height at withers and depth at breast times two (M1-2xM4), as it gives better comparison of the leg length to consider the variation in breast depth between different horses.
- visualization of the genomic-kinship matrix using MDS is shown in Fig.
- The haplotype effect on the score of back and croup was estimated by a gereralized linear model (glm) with the function haplo.glm..
- Phenotype association of the horses homozygous for the haplotypes that had a significant effect on the conform- ation of back and croup was performed using a two- tailed Student’s t-test in R [70].
- Genotyping of the top SNP and DMRT3 in other gaited and partly gaited breeds.
- The sequence of the primers and probes was designed as follows: forward pri-.
- SNP genotyping of the DMRT3_Ser301STOP marker known as the “Gait Keeper” mutation was performed using custom designed TaqMan SNP Genotyping Assays (Applied Biosystem) as described previously [30, 34]..
- 5 MDS plot for the score back and croup.
- Visualization of population stratification across the 177 Icelandic horses that passed the QC for the score back and croup.
- Heimir Gunnarsson breeding leader of the Icelandic horse breeding association in Sweden for sharing valuable information and thoughts.
- MKR, HS, SE, MNB, EA, TK, MR, ÅV, BDV, JJN, MS and GL contributed to the interpretation of the results.
- However, data is available from the corresponding author on reasonable request and with permission of the Icelandic horse association..
- The authors declare competing interest concerning commercial applications of the current study.
- GL is a co-inventor on a patent application concerning commercial testing of the DMRT3 mutation.
- The stated patents does not re- strict research applications of the method..
- characterization of the Menorca horse at the walk and the trot: influence of hind limb pastern angle.
- Worldwide frequency distribution of the ‘ Gait keeper ’ mutation in the DMRT3 gene.
- The coexistence of copy number variations (CNVs) and single nucleotide polymorphisms (SNPs) at a locus can result in distorted calculations of the significance in associating SNPs to disease.
- Proceedings of the International Research Society of Spinal Deformities conference.
- There may be a same mechanism of the left-right handedness and left-right convex curve pattern of adolescent idiopathic scoliosis.
- Disorders of the thoracolumbar spine of the horse — a survey of 443 cases.
- The laterality of the gallop gait in Thoroughbred racehorses

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