Genetic Studies on Conformation and Performance of IcelandicToelterHorses

Speed of gaits in Icelandic horses and relationships to sex, age, conformation measurements and subjective judges’ scores

The aim was to measure the mean and maximum speed and the range of speed in all gaits of Icelandic horses shown at a breed evaluation field test (BEFT). In addition, the effect of speed on scores for the gaits and whether speed was affected by age, sex and conformation measurements were investigated. The study was carried out in Iceland on 266 horses (180 mares and 86 stallions). Horse speed and distance ridden were recorded by global positioning system during the riding assessment in BEFT. Conformation measurements and scores for each gait were obtained from the official studbook Worldfengur. The range of speed in walk, slow tölt, tölt, trot, pace, canter and gallop was, respectively, 1.5-2.2, 3.2-5.5, 4.6-10.6, 4.5-8.6, 7.1-11.9, 5.8-9.8 and 7.9-13.5 m/s (n=149-248). Scores for all gaits were affected by speed of the gait, with speed explaining most variance in scores for pace (53%) and least in scores for slow tölt and walk (2 and 3%, respectively). Stallions were faster than mares in tölt, trot, pace and canter (P<0.05). Horses aged ≥7 years and 6-year-olds were faster in pace and canter than 4-year-olds (P<0.05). Horse conformation measurements most affected speed in pace and walk, which were elevated with increased height at withers, height at croup, body length and length of front legs (P<0.05). In conclusion, objective measurements of speed in the gaits of Icelandic horses shown in a BEFT were documented for the first time. The information can be used to formulate requirements for gaits in BEFT and in competition manuals. Objective measurements of speed should be used in future assessments of gaits in Icelandic horses in BEFT, and thus improve standardisation and genetic evaluation of breeding horses.

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.

Expression levels of LCORL are associated with body size in horses

Body size is an important characteristic for horses of various breeds and essential for the classification of ponies concerning the limit value of 148 cm (58.27 inches) height at the withers. Genome-wide association analyses revealed the highest associated quantitative trait locus for height at the withers on horse chromosome (ECA) 3 upstream of the candidate gene LCORL. Using 214 Hanoverian horses genotyped on the Illumina equine SNP50 BeadChip and 42 different horse breeds across all size ranges, we confirmed the highly associated single nucleotide polymorphism BIEC2-808543 (−log₁₀P = 8.3) and the adjacent gene LCORL as the most promising candidate for body size. We investigated the relative expression levels of LCORL and its two neighbouring genes NCAPG and DCAF16 using quantitative real-time PCR (RT-qPCR). We could demonstrate a significant association of the relative LCORL expression levels with the size of the horses and the BIEC2-808543 genotypes within and across horse breeds. In heterozygous C/T-horses expression levels of LCORL were significantly decreased by 40% and in homozygous C/C-horses by 56% relative to the smaller T/T-horses. Bioinformatic analyses indicated that this SNP T>C mutation is disrupting a putative binding site of the transcription factor TFIID which is important for the transcription process of genes involved in skeletal bone development. Thus, our findings suggest that expression levels of LCORL play a key role for body size within and across horse breeds and regulation of the expression of LCORL is associated with genetic variants of BIEC2-808543. This is the first functional study for a body size regulating polymorphism in horses and a further step to unravel the mechanisms for understanding the genetic regulation of body size in horses.

Efeito da endogamia sobre características morfométricas em cavalosda raça Mangalarga Marchador

Estimou-se o coeficiente de endogamia e avaliou-se seu efeito sobre características morfométricas dos animais em um criatório no norte de Minas Gerais. As características estudadas foram alturas da cernelha e da garupa, comprimentos da cabeça, do pescoço, do dorso-lombo, da garupa e do corpo, larguras do peito e da garupa. O arquivo continha 2186 informações de parentesco de animais do arquivo zootécnico da fazenda, desde o início da formação da raça, 1951, até o ano de 2006. Calculou-se o coeficiente de endogamia (F) e avaliou-se seu efeito por meio de regressão linear simples sobre as medidas morfométricas. Do total de animais, 27,6% mostraram-se endogâmicos, sendo o F médio da população igual a 1,4%. Considerando-se apenas os animais endogâmicos, a consanguinidade média atingiu 5,3%, mínimo de 0,1 e máximo de 28,1%. Não se verificaram efeitos negativos da endogamia sobre as características morfométricas, exceto para largura da garupa, em que se observou que para cada 10% de acréscimo de F houve aumento de 0,576cm na largura da garupa. Possivelmente, devido ao baixo valor encontrado, a endogamia não influenciou as demais características avaliadas.

Estimates of genetic parameters for conformation measures and scores in Finnhorse and Standardbred foals

The aim of this study was to estimate genetic parameters for conformation measures and scores in the Finnhorse and the Standardbred foals presented in foal shows. Studied traits included height at withers and at croup, six subjectively evaluated conformation traits and overall grade. Data were from 10-year period (1995-2004) and consisted of 5821 Finnhorse foals (1-3 years old) with 7644 records and 2570 Standardbred foals (1-2 years old) with 2864 records. Variance components were estimated with REML - animal model using VCE4 program. The model included age class, year of judging, sex and region as fixed effects, and additive genetic, permanent environmental and residual as random effects. Estimates of heritability for measured traits were very high in both breeds (0.88-0.90). Estimates of heritability for conformation traits varied from 0.13 to 0.32 in the Finnhorse and from 0.06 to 0.47 in the Standardbred. In both breeds, estimates of heritability were lowest for hooves and movements at walk, and highest for type and body conformation among scored traits. Estimate of heritability for overall grade was in the Finnhorse 0.32 and in the Standardbred 0.34. Genetic correlations between overall grade and different conformation traits were 0.35-0.84 in the Finnhorse and 0.31-0.88 in the Standardbred. Thus, selection based on the overall grade would improve all studied characteristics.

Multi-trait animal model estimation of genetic parameters for linear type and gait traits in the Belgian warmblood horse

Genetic parameters for the height at withers, 27 linear type and six linear gait traits were estimated for the Belgian warmblood horse. Observations on 987 mares, mostly 3 years old, were analysed using a multi-trait animal model. The statistical model included appraiser, age and location (date x place of appraisal) as fixed effects. Genetic parameters were estimated using a canonical transformation and an expectation-maximization restricted maximum likelihood algorithm with an additional deceleration step. Estimates of heritability for the 33 linear traits were between 0.15 and 0.55. Heritability of the height at withers was 0.34 +/- 0.06. Estimated genetic correlations ranged from -0.60 to 0.98 with an average SE of 0.10. The highest positive correlations were found among traits of walk and among traits of trot. Volume and the quality of legs were the most negatively correlated. Estimated genetic parameters indicated that the linear scoring system is a valuable tool to assess conformation. The full (co)variance matrix is now available for breeding value estimation to support selection for conformation and gaits.

Associação entre medidas lineares e angulares de equinos da raça Mangalarga Marchador

Foram analisadas 12 medidas de comprimento dos ossos, duas medidas de altura, duas medidas de perímetro e 11 medidas de ângulos articulares) de 169 equinos da raça Mangalarga Marchador, de ambos os sexos (82% de fêmeas), com idades entre 35 e 269 meses, de 11 criatórios do Estado de Minas Gerais e cinco de São Paulo. Os efeitos de estado e criatório de origem, tipo de criação (baia ou pasto), idade e sexo sobre essas características foram avaliados pelo método dos quadrados mínimos, e as associações entre as características foram quantificadas por meio da correlação de resíduos. Os modelos justificaram pouco da variação observada, com coeficientes de determinação variando de 0,09 a 0,48 para as medidas lineares e de 0,11 a 0,44 para as medidas angulares. Estado e criatório de origem, sexo, idade e tipo de criação foram importantes fontes de variação, respectivamente para 13 (48,1%), 12 (44,4%), seis (22,2%), quatro (14,8%) e três (11,1%) das 27 características avaliadas. As correlações de resíduo entre as características indicaram que a escolha de animais com úmero de maior comprimento está associada a animais com membros torácicos e pélvicos mais longos e que a escolha de animais a partir do tamanho dos membros acarretará concomitante incremento na altura da cernelha e na garupa e do perímetro da canela e torácico. Ainda, a escolha dos animais considerando as medidas dos ângulos metacarpofalangeano e dedo torácico com a horizontal refletirá positivamente na altura da cernelha e da garupa.

Radiographic closure time of appendicular growth plates in the Icelandic horse

Background

The Icelandic horse is a pristine breed of horse which has a pure gene pool established more than a thousand years ago, and is approximately the same size as living and extinct wild breeds of horses. This study was performed to compare the length of the skeletal growth period of the "primitive" Icelandic horse relative to that reported for large horse breeds developed over the recent centuries. This information would provide practical guidance to owners and veterinarians as to when the skeleton is mature enough to commence training, and would be potentially interesting to those scientists investigating the pathogenesis of osteochondrosis. Interestingly, osteochondrosis has not been documented in the Icelandic horse.

Methods

The radiographic closure time of the appendicular growth plates was studied in 64 young Icelandic horses. The results were compared with previously published closure times reported for other, larger horse breeds. The radiographs were also examined for any signs of developmental orthopaedic diseases. In order to describe further the growth pattern of the Icelandic horse, the total serum alkaline phosphatase (ALP) activity was determined and the height at the withers was measured.

Results

Most of the examined growth plates were fully closed at the age of approximately three years. The horses reached adult height at this age; however ALP activity was still mildly increased over baseline values. The growth plates in the digits were the first to close at 8.1 to 8.5 months of age, and those in the regions of the distal radius (27.4 to 32.0 months), tuber olecrani (31.5 to 32.2 months), and the stifle (27.0 to 40.1 months) were the last to close. No horse was found to have osteochondrosis type lesions in the neighbouring joints of the evaluated growth plates.

Conclusion

The Icelandic horse appears to have similar radiographic closure times for most of the growth plates of its limbs as reported for large new breeds of horses developed during the past few centuries. It thus appears that different breeding goals and the intensity of breeding have not altered the length of the growth period in horses. Instead, it can be assumed that the pristine and relatively small Icelandic horse has a slower rate of growth. The appendicular skeleton of Icelandic horses has completed its bone growth in length at approximately 3 years of age, and therefore may be able to enter training at this time.

Dressage scoring patterns at selected British Eventing novice events

Subjective bias by judges within the dressage phase of eventing competition is problematic if correct evaluation of horse and rider performance is to be undertaken. The present study examines dressage penalty scoring (penalty scores are awarded for completion of a pre-set series of dressage movements) within a population of novice event horses (n = 2471). Between May and June 2003, 22 novice events within the UK were analysed, and at each event up to six competitions or sections (at the same competitive level) were run. The whole population data structure was normal in distribution, Pearson's skewness 0.314 (Kolmogorov–Smirnov Z = 1.855, P>0.05 from zero) and kurtosis at 0.425. The mean score recorded for the whole population was 37.82 penalty points (standard deviation = 5.65 and standard error = 0.11). A number of effects were observed within the population. Between-events effects were observed in three of the 22 events studied (P<0.01). Of those events running three or more sections (n = 16), within-event effects were observed for 10 events as differences (P<0.01) in mean scoring patterns between sections. All events running two sections (n = 4) were observed to exhibit differences (P<0.02) in mean scores. Differences (P>0.01) between the dressage test used at events were determined using post hoc Bonferroni tests. However, these differences were not found to have a confounding effect on the between-event observations. The study indicates that additional methodologies need to be implemented to ensure that accurate and impartial evaluation of event horses is conducted.

Prevalence and risk factors of bone spavin in Icelandic horses in Sweden: a radiographic field study

The present field study was performed to estimate the prevalence of radiographic signs of bone spavin (RSBS) and to evaluate some possible risk factors for RSBS in the Icelandic horse in Sweden. The survey included horses from 11 farms involving 379 horses, comprising 238 geldings, 125 mares and 16 stallions. Age ranged from 0 to 19 years with a mean age of 8.1 years. Horses were radiographed with a dorsolateral-plantaromedial-oblique projection of both tarsi. Information about age, gender, origin, working intensity, number of gaits and age when saddle broken were obtained by interviewing the owners. Features of each horse's conformation were obtained by measurement or inspection. Radiographic signs of bone spavin were found in 23% (n = 88) of the horses. Horses younger than 5 years did not show any RSBS and the prevalence increased from zero to 33% between 4 and 8 years of age. Using a multivariate logistic regression model increasing age and sickle hock conformation were found to be significantly associated with increased risk of RSBS. Age when saddle broken in combination with height at the withers also influenced the multivariate logistic regression model significantly.