Native Horse Breeds Research Articles

Genetic diversity and signatures of selection in Icelandic horses and Exmoor ponies

BackgroundThe Icelandic horse and Exmoor pony are ancient, native breeds, adapted to harsh environmental conditions and they have both undergone severe historic bottlenecks. However, in modern days, the selection pressures on these breeds differ substantially. The aim of this study was to assess genetic diversity in both breeds through expected (HE) and observed heterozygosity (HO) and effective population size (Ne). Furthermore, we aimed to identify runs of homozygosity (ROH) to estimate and compare genomic inbreeding and signatures of selection in the breeds.ResultsHO was estimated at 0.34 and 0.33 in the Icelandic horse and Exmoor pony, respectively, aligning closely with HE of 0.34 for both breeds. Based on genomic data, the Ne for the last generation was calculated to be 125 individuals for Icelandic horses and 42 for Exmoor ponies. Genomic inbreeding coefficient (FROH) ranged from 0.08 to 0.20 for the Icelandic horse and 0.12 to 0.27 for the Exmoor pony, with the majority of inbreeding attributed to short ROHs in both breeds. Several ROH islands associated with performance were identified in the Icelandic horse, featuring target genes such as DMRT3, DOCK8, EDNRB, SLAIN1, and NEURL1. Shared ROH islands between both breeds were linked to metabolic processes (FOXO1), body size, and the immune system (CYRIB), while private ROH islands in Exmoor ponies were associated with coat colours (ASIP, TBX3, OCA2), immune system (LYG1, LYG2), and fertility (TEX14, SPO11, ADAM20).ConclusionsEvaluations of genetic diversity and inbreeding reveal insights into the evolutionary trajectories of both breeds, highlighting the consequences of population bottlenecks. While the genetic diversity in the Icelandic horse is acceptable, a critically low genetic diversity was estimated for the Exmoor pony, which requires further validation. Identified signatures of selection highlight the differences in the use of the two breeds as well as their adaptive trait similarities. The results provide insight into genomic regions under selection pressure in a gaited performance horse breed and various adaptive traits in small-sized native horse breeds. This understanding contributes to preserving genetic diversity and population health in these equine populations.

Using high-density SNP data to unravel the origin of the Franches-Montagnes horse breed

BackgroundThe Franches-Montagnes (FM) is the last native horse breed of Switzerland, established at the end of the 19th century by cross-breeding local mares with Anglo-Norman stallions. We collected high-density SNP genotype data (Axiom™ 670 K Equine genotyping array) from 522 FM horses, including 44 old-type horses (OF), 514 European Warmblood horses (WB) from Sweden and Switzerland (including a stallion used for cross-breeding in 1990), 136 purebred Arabians (AR), 32 Shagya Arabians (SA), and 64 Thoroughbred (TB) horses, as introgressed WB stallions showed TB origin in their pedigrees. The aim of the study was to ascertain fine-scale population structures of the FM breed, including estimation of individual admixture levels and genomic inbreeding (FROH) by means of Runs of Homozygosity.ResultsTo assess fine-scale population structures within the FM breed, we applied a three-step approach, which combined admixture, genetic contribution, and FROH of individuals into a high-resolution network visualization. Based on this approach, we were able to demonstrate that population substructures, as detected by model-based clustering, can be either associated with a different genetic origin or with the progeny of most influential sires. Within the FM breed, admixed horses explained most of the genetic variance of the current breeding population, while OF horses only accounted for a small proportion of the variance. Furthermore, we illustrated that FM horses showed high TB admixture levels and we identified inconsistencies in the origin of FM horses descending from the Arabian stallion Doktryner. With the exception of WB, FM horses were less inbred compared to the other breeds. However, the relatively few but long ROH segments suggested diversity loss in both FM subpopulations. Genes located in FM- and OF-specific ROH islands had known functions involved in conformation and behaviour, two traits that are highly valued by breeders.ConclusionsThe FM remains the last native Swiss breed, clearly distinguishable from other historically introgressed breeds, but it suffered bottlenecks due to intensive selection of stallions, restrictive mating choices based on arbitrary definitions of pure breeding, and selection of rare coat colours. To preserve the genetic diversity of FM horses, future conservation managements strategies should involve a well-balanced selection of stallions (e.g., by integrating OF stallions in the FM breeding population) and avoid selection for rare coat colours.

Insular dwarfism in horses from the Aegean Sea and the Japanese archipelago

The horse (Equus caballus) varieties from Skyros and Rhodes islands (Greece) in the Aegean archipelago are extremely small, reaching shoulder heights of only about 1 m. Furthermore, the Japanese archipelago is home to eight small, native horse breeds. We investigated the evolutionary morphology and provided a review of historical documentations of these horses of cultural interest in Greece and Japan, thus providing a comparison of the independent evolution of small size in islands. We integrate cranial data from historical literature with data from newly gathered and curated skulls and analyse a measurement dataset featuring various domestic and mainland horse breeds and varieties. We use non-invasive imaging to study and measure 3D models of the bony labyrinth, housing the inner ear, and the braincase endocast. When considering the effects of allometry by regressing each PC1 scores (for each set of measurements) with the cranial geometric mean from linear measurements as a body size proxy, we show that size explains a large amount of the shape variation in horse crania, the bony labyrinths and brain endocasts. We found high intrabreed variation in all the analysed datasets. Globally, there are at least 30 distinct horse populations on islands, offering the chance to further study processes of convergence in morphological divergence and evaluate the effect of drift and the environment.

Assessment of Native Lithuanian Horses for Therapeutic Riding Purposes

ABSTRACT Hippotherapy is considered as a beneficial field of activity for Žemaitukas, a Lithuanian native horse breed. The aim of this study is to analyze the suitability of Žemaitukas breed horses for hippotherapy by using a set of tests based on the temperament, behavioral reactions, and zoometric measurements. Results of these tests inform whether the future use of Lithuanian native horses in hippotherapy can ensure their welfare. In total, 32 horses were evaluated. Twenty-nine of the evaluated horses were horses of the Žemaitukas breed that had never been used for hippotherapy, the others were hippotherapy horses representing different breeds, which were considered the control group. As expected, control hippotherapy horses scored better in many tests, thus confirming the suitability of these tests for the evaluation of horses for hippotrapeutic use. Žemaitukas breed horses scored an average of 15.9% less points for the test of temperament and 21.3% less points for “Hippo-test” compared with the hippotherapy horses. Nevertheless, the results suggest that Žemaitukas breed horses could be used in hippotherapy after special training courses.

Study Regarding the Genetic Relationship between Broodmares from the Reproductive Nucleus of a Native Horse Breed

Background: In this study we present a part of the genetic history of a native horse breed. Genetic analyzes are the basis of the development of strategies regarding the conservation of genetic resources and implicitly of inbreeding management plan. In this study we present another essential component of the inbreeding of a population, namely the inbreeding of broodmares themselves. Method: The method that we used in this study is based on A matrix coefficients. The research was carried out during 2012-2021, at Lucina National stud farm. The material was represented by a sample of 73 broodmares from the reproductive nucleus of the breed, from 5 bloodlines, analyzed on 5 generation of ascendants. The research was performed in the profile laboratories of the Faculty of Engineering and Management in Animal Production (Animal Sciences) from Bucharest. Results: The correlation between the breeding values of the reproductive active broodmares of Huþul from the Lucina stud, Suceava County, at the time of the analysis is 0.1875±0.0015. It was found the existence some differences between the values of the kinship coefficients of the mares born in different years, but the calculated value of the Fisher test (F= 1.3667NS) shows that the observed differences have no statistical significance.

Y-Chromosome Haplotype Report among Eight Italian Horse Breeds.

Horse domestication and breed selection processes have profoundly influenced the development and transformation of human society and civilization over time. Therefore, their origin and history have always attracted much attention. In Italy, several local breeds have won prestigious awards thanks to their unique traits and socio-cultural peculiarities. Here, for the first time, we report the genetic variation of three loci of the male-specific region of the Y chromosome (MSY) of four local breeds and another one (Lipizzan, UNESCO) well-represented in the Italian Peninsula. The analysis also includes data from three Sardinian breeds and another forty-eight Eurasian and Mediterranean horse breeds retrieved from GenBank for comparison. Three haplotypes (HT1, HT2, and HT3) were found in Italian stallions, with different spatial distributions between breeds. HT1 (the ancestral haplotype) was frequent, especially in Bardigiano and Monterufolino, HT2 (Neapolitan/Oriental wave) was found in almost all local breeds, and HT3 (Thoroughbred wave) was detected in Maremmano and two Sardinian breeds (Sardinian Anglo-Arab and Sarcidano). This differential distribution is due to three paternal introgressions of imported stallions from foreign countries to improve local herds; however, further genetic analyses are essential to reconstruct the genetic history of native horse breeds, evaluate the impact of selection events, and enable conservation strategies.

Genetic characterization of Japanese native horse breeds by genotyping variants that are associated with phenotypic traits.

Concerns have been raised about the loss of genetic diversity in Japanese native horses because of their declining populations. In this study, we investigated the genetic variation of four genes, myostatin (MSTN), ligand-dependent nuclear receptor corepressor like (LCORL), doublesex and mab-3 related transcription factor 3 (DMRT3), and 5-hydroxytryptamine receptor 1A (HTR1A), which are associated with horse phenotypic traits, in six Japanese horse breeds (Hokkaido, Kiso, Noma, Misaki, Tokara, and Yonaguni). MSTN, LCORL, DMRT3, and HTR1A showed polymorphisms in the Kiso; Hokkaido and Noma; Hokkaido; and Kiso, Tokara, and Yonaguni breeds, respectively. The Misaki did not show polymorphisms in any of the genes. This study may serve as a basis for developing future breeding strategies focusing on traits in Japanese native horses.

Mitochondrial DNAD-loop hyper-variable region 1 variability in Kurdish horse breed.

Kurdish horse is one of the most valuable horse genetic resources in the Middle East. To assess the genetic diversity of Kurdish horses, Mitochondrial DNA D-loop hyper-variable region1 (HVR1) was sequenced in 29 non-related Kurdish horses which were sampled from diverse geographic regions of Iran. Total DNA was extracted from the collected blood samples by modified salting out method. The HVR1 was amplified by PCR and then sequenced using ABI PRISM BigDyeTM Terminator Cycle Sequencing Ready Reaction Kit. Consequently, the sequences were trimmed to 294bp using BIOEDIT to become comparable with other reported HVR1 sequences in GeneBank. Sequence alignment was performed using CLUSTALW package. Haplotype and nucleotide diversity were estimated using DNASP5.10 and phylogenetic tree was constructed by neighbour joining method. Fourteen different haplotypes and 22 polymorphic sites were detected. Haplotype diversity, nucleotide diversity and Tajima D values were 0.901 ± 0.001, 0.01153 ± 0.0020 and -1.378, respectively. Kurdish horse showed a high haplotype and low nucleotide diversity. The compositional frequency of consensus sequences for base A was the highest (29.93%) compared to other three nucleotides (C = 28.91%, T = 26.53% and G = 14.63%). As expected, all of the detected Kurdish horse haplotypes belonged to haplogroup K (i.e., Kurdish horses). According to the phylogenetic analysis, Kurdish horses were genetically more closely related to Tibetan, Chinese, Bulgarian and Iranian native horse breeds, compared to other Asian horse breeds, but some traces of European horse breeds were detected in their maternal lines.

Memories, museum artefacts and excavations in resolving the history of maternal lineages in the Finnhorse.

We used historical DNA samples to examine the history of a native horse breed, the Finnhorse. Samples were collected from private collections, museums, schools and excavations, representing the times prior to, during, and after the foundation of the breed; from the end of the 19th century and throughout the 20th century. We sequenced a fragment of mitochondrial DNA from these historical samples to study the history and evolution of maternal lineages of horses back to the early days of the breed, compared the mitochondrial DNA sequence diversity of different historical periods and modern day Finnhorses, estimated the effective population sizes, and searched for both temporal and geographic population genetic structure. We observed high maternal haplotype and nucleotide diversity at the time during the foundation of the breed, and a decrease in both measures during 1931-1970. In addition, we observed losses of some haplotypes present in the early stages of the breed. There was only slight evidence of geographical or temporal population structure. This study is, to our knowledge, the first to use such temporal sampling to reveal the history of a specific animal breed.

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.

Preliminary Results Regarding the Genetic History of a Native Horse Breed- Genetic Relationship between Sire Stallions and Broodmares

Background: This study is a part of an ample research concerning the genetic history of Hucul horse breed. The genetic analysis studies are part of animal genetic resources Management because just start of them we elaborate the strategies for inbreeding management. The itself genetic relationship of a population is the average genetic relationship of all individuals between them, existing at a time. Therefore, this parameter can be described three components: the genetic relationship between stallions, between mother mares themselves and the genetic relationship between stallions and mares. The last component is most important because of the average population inbreeding increases in successive generations. Methods: The research was carried out during 2012-2020. The material are represented by genealogical information from reproductive nucleus of Hucul breed from Lucina studfarm. The sample extracted from population was represented by seven sire stallions and seventy-three broodmares. The method are based on A matrix coefficients. All analysis were performed in the profile laboratories of Animal Sciences Faculties from Bucharest and Timisoara. Result: Between individual average genetic relationship values of stallions with mares, is found significant differences, highlighted by the global test of homogeneity test (F = 4.891). These differences allow us to assert that, through stallions selection, is made a reproductive discrimination much more intense than in mares case. The average genetic relationship of the population was calculated at 0.1941±0.0053.

Monitoring Body Length of Hokkaido Native Horse’s Foals Using a Drone

Monitoring Body Length of Hokkaido Native Horse’s Foals Using a Drone

Determination of different predictors affecting DNA concentration isolated from historical hairs of the Finnhorse

Everyday objects manufactured from raw materials of animal origin, such as skin, hair and bone, are innumerable in cultural historical museums and private collections. Besides their value as memoirs of past techniques, livelihoods and communities, they are a unique source for studying past animal populations by means of molecular analysis.Here, we deal with horse mane and tail hair, a type of predecessor of modern synthetic material utilized, for example, for brushes, strings, tennis rackets, ropes, textiles, dolls’ hair, rocking horses, and filling. By investigating the presence and quality of DNA in horsehair, we have studied the origins of the Finnhorse, the only native horse breed in Finland. Degradation of DNA in old samples is an issue that needs to be considered when selecting material for DNA analysis. For assessing the usability of historical artefacts for DNA-based studies, we study how DNA is preserved in horsehair and how well DNA can be isolated from 50 to 150-year-old artefacts, raw material bundles and archaeological finds. We investigate how the properties of hair and sample storage conditions affect the concentration of DNA extracts and success in Polymerase Chain Reaction (PCR).Our analysis showed that historical hair shafts, stored in various environments and used for multiple purposes, are of sufficient quantity and quality for amplification by PCR. Therefore, their value for the research of past animal populations should be noticed when curating cultural historical collections. We also provide advice for the storage conditions for hair samples.

A Novel QTL and a Candidate Gene Are Associated with the Progressive Motility of Franches-Montagnes Stallion Spermatozoa after Thaw.

The use of frozen-thawed semen is an important reproduction tool to preserve the biodiversity of small, native horse breeds such as the Franches-Montagnes (FM). However, not all stallions produce cryotolerant semen with a progressive motility after thaw ≥ 35%. To improve our understanding of the genetic background of male fertility traits in both fresh and frozen-thawed semen, we performed genome-wide association studies (GWAS) on gel-free volume, sperm cell concentration, total sperm count, and progressive motility in fresh and frozen-thawed semen from 109 FM stallions using 335,494 genome-wide single nucleotide polymorphisms (SNPs). We identified one significant (p < 1.69 × 10−7) quantitative trait locus (QTL) on ECA6 within the SCN8A gene for progressive motility after thaw, which was previously associated with progressive motility in boars. Homozygous stallions showed a substantial drop in progressive motility after thaw. This QTL could be used to identify cryointolerant stallions, avoiding the costly cryopreservation process. Further studies are needed to confirm whether this QTL is also present in other horse breeds.

Application of modern technologies in identifying distinctive features in the subpopulation of Novoaltaiskaya horses

Novoaltaiskaya meat horse breed was developed in the end of the XX century by crossing heavy draft sires of different breeds with native and crossbred Altai mares. The aim of the study was to evaluate the differences in two geographically separated subpopulations of horses of Novoaltaiskaya breed and their relationship with the Altaiskaya horse using 17 panel microsatellite loci (VHL20, HTG4, AHT4, HMS7, HTG6, AHT5, HMS6, ASB23, ASB2, HTG10, HTG7, HMS3, HMS2, ASB17, LEX3, HMS1 and CA425). The horses of Novoaltaiskaya breed demonstrated a high level of variability of all 17 STR loci with calculated 148 alleles in total. In the genetic structure of Novoaltaiskaya horse breed we identified the rare alleles VHL20S, ASB23V, ASB2T, HMS1Q, HMS2S, HMS3S and CA425K that are typical of native horse breeds of our country. A comparative analysis of the four groups according to the main genetic and population characteristics showed that the horses of the «Merkit» subpopulation (Altai Republic) are leading in all parameters of genetic diversity, including the maximum level of polymorphism (Ae=4.959), the level of observed heterozygosity Ho (0.776), and the expected heterozygosity of He (0.758). That ensured a negative Fis value. The coefficient of genetic similarity between two subpopulations of Novoaltaiskaya horses was 0,935. Thus, the use of genetic biotechnology allowed us to identify rare and frequently occurring alleles in the subpopulation of Novoaltaiskaya horses.

Selection in the Finnhorse, a native all-around horse breed.

Selection by breeders modifies the morphology, behaviour and performance of domesticated species. Here, we examined signs of selection in Finnhorse, the only native horse breed in Finland. We first searched divergent genomic regions between Finnhorses and other breeds, as well as between different breeding sections of the Finnhorse with data from Illumina Equine SNP70 BeadChip, and then studied several of the detected regions in more detail. We found altogether 35 common outlier SNPs between Finnhorses and other breeds using two different selection tests. Many of the SNPs were located close to genes affecting coat colour, performance, size, sugar metabolism, immune response and olfaction. We selected genes affecting coat colour (KIT, MITF, PMEL), performance (MSTN) and locomotion (DMRT3) for a more detailed examination. In addition, we looked for, and found, associations with height at withers and SNPs located close to gene LCORL. Among the four breeding sections of Finnhorses (harness trotters, riding horses, draught horses and pony‐sized horses), a single SNP located close to the DMRT3 gene was significantly differentiated and only between harness trotters and pony‐sized horses.

Polymorphism of DMRT3 Gene and Its Association with Body Measurements in Horse Breeds

The double sex and mab-3-related transcription factor 3 gene (DMRT3) placed on chromosome 23 of equine. This gene codes a major transcription factor in the spinal cord complex encompasses regulating motion of vertebrates. It is implicated in a neural network for the synchrony of the moving apparatus that governs limb motion. The aim of this study was to determine polymorphism of DMRT3 gene in Iranian exotic and native horse breeds (Persian Arab, Akhal teke, Yamut, Kurd, Dareshouri, Caspian, Taleshi) using of PCR-RFLP technique and its correlation with body measurements. DNA was extracted from blood samples of 374 horses and a 485-bp fragment within the horse DMRT3 gene was synthesized applying specific primers. The PCR products were digested with DdeI restriction enzyme at 37??C overnight, and the resulting products were separated by the 3.5% agarose gel and visualized by ethidium bromide staining. Body measurements and gene association analyses were performed using a statistical model containing the fixed effects of breed, sex and the animal genotype for the DMRT3 locus. In all of the studied populations two genotypes, CC and AC, were observed while AA was not observed. Frequencies of C and A alleles were 0.97 and 0.03%, respectively. The AC genotype was only observed in Iranian native breeds including Turkmen (Akhal teke), Turkmen (Yamut), Dareshouri, Kurd and Caspian, while the other 12 remained breeds had only CC genotype. Number of observed alleles, number of effective alleles, observed heterozygosity, expected heterozygosity, Shanon???s index, Nei???s index and fixation index (Fis) for all studied breeds were 2.00, 1.06, 0.06, 0.06, 0.14, 0.06 and 0.10, respectively. A UPGMA dendrogram based on the Nei???s standard genetic interval between studied breeds displayed distinct clusters for Iranian native and exotic breeds. Statistical association analysis of two observed genotypes with body measurements showed that the studied mutation has no effect on body measurements.

A Genetic Window on Sardinian Native Horse Breeds through Uniparental Molecular Systems.

Simple SummaryThe horse is a mammalian species showing a high variation among maternal lineages but a limited variability in the paternal inheritance. The female phylogenetic history is commonly investigated by analyzing the maternally transmitted mitochondrial DNA (mtDNA), while the male perspective is provided by the paternally inherited portion of the Y chromosome (NRY). Here we explored the variation of both non-recombining genetic systems in three horse breeds present in Sardinia: Giara, Sarcidano, and Sardinian Anglo-Arab. The analysis of 34 stallions revealed three differentially distributed NRY types: (i) the first and most ancestral one is typical of Sarcidano; (ii) the second is well represented in Giara and seems to derive from Neapolitan/Oriental stallions; (iii) the third confirms the Thoroughbred influence in the Sardinian Anglo-Arab breed. By extending the analysis to 178 mtDNAs, we observed a common maternal origin for Giara and Sarcidano. Contrarily, the outlier behavior of the Sardinian Anglo-Arab is due to its higher mitochondrial variability, testifying for multiple maternal lineages in its current population. Our preliminary findings highlight the importance of a parallel molecular screening of NRYs and mtDNAs to reconstruct both paternal and maternal phylogenetic histories and to fully evaluate the extent of autochthonous genetic resources in the island.Sardinia, an island located to the west of Italy in the Mediterranean Sea, boasts three native horse breeds: Giara, Sarcidano, and Sardinian Anglo-Arab. Here, we have investigated for the first time three loci of the non-recombining region of the Y chromosome (NRY) in 34 stallions from these breeds and performed a phylogenetic analysis of the maternal relationships among 178 previously published mitochondrial control regions. We found that the current NRY diversity of Sardinian horse breeds is linked to three haplotypes (HT), all identified within Sarcidano. Each breed showed a typical HT: HT1 (ancestral) was the most represented in Sarcidano, HT2 (Neapolitan/Oriental wave) in Giara, and HT3 (Thoroughbred wave) in Sardinian Anglo-Arab. The specificity of each haplotype suggests the influence of independent breeding strategies and the effect of genetic drift in each Sardinian population. The female counterpart, extended to 178 horses, showed a low genetic variability and a common maternal origin for Giara and Sarcidano. The higher variability of the Sardinian Anglo-Arab indicates multiple mare lineages in its current population. Further genetic analyses will be crucial to understand the paternal history of male horses, preserve the endangered mares’ and stallions’ lineages, and improve the enhancement of autochthonous genetic resources on this island.

Genetic Diversity and Signatures of Selection in a Native Italian Horse Breed Based on SNP Data.

Simple SummaryThe Bardigiano horse is a native Italian breed bred for living in rural areas, traditionally used in agriculture. The breed counts about 3000 horses, and it is nowadays mainly used for recreational purposes. The relatively small size and the closed status of the breed raise the issue of monitoring genetic diversity. We therefore characterized the breed’s genetic diversity based on molecular data. We showed a critical reduction of genetic variability mainly driven by past bottlenecks. We also highlighted homozygous genomic regions that might be the outcome of directional selection in recent years, in line with the conversion of Bardigiano horses from agricultural to riding purposes.Horses are nowadays mainly used for sport and leisure activities, and several local breeds, traditionally used in agriculture, have been exposed to a dramatic loss in population size and genetic diversity. The loss of genetic diversity negatively impacts individual fitness and reduces the potential long-term survivability of a breed. Recent advances in molecular biology and bioinformatics have allowed researchers to explore biodiversity one step further. This study aimed to evaluate the loss of genetic variability and identify genomic regions under selection pressure in the Bardigiano breed based on GGP Equine70k SNP data. The effective population size based on Linkage Disequilibrium (Ne) was equal to 39 horses, and it showed a decline over time. The average inbreeding based on runs of homozygosity (ROH) was equal to 0.17 (SD = 0.03). The majority of the ROH were relatively short (91% were ≤2 Mbp long), highlighting the occurrence of older inbreeding, rather than a more recent occurrence. A total of eight ROH islands, shared among more than 70% of the Bardigiano horses, were found. Four of them mapped to known quantitative trait loci related to morphological traits (e.g., body size and coat color) and disease susceptibility. This study provided the first genome-wide scan of genetic diversity and selection signatures in an Italian native horse breed.

Linkage disequilibrium, haplotype blocks and historical effective population size in Arabian horses and selected Polish native horse breeds

This study was conducted to investigate linkage disequilibrium (LD), historical effective population size (Ne) and haplotype block structures in genomes of highly selected Polish Arabian (AR; n=124) horses and conserved horse breeds derived from Polish native breeds, in particular, Malopolski (MLP; n=56), Sokolski (SOK; n=107), Sztumski (SZTUM; n=69), Hucul (HC; n=116) and Polish Konik (KN; n=99) horses, based on single nucleotide polymorphisms (SNPs) from the Neogen Equine Community BeadChip assay (Illumina, San Diego, CA). LD analysis was performed based on the pairwise r2 statistic of SNPs at a distance up to 5Mb. At a short distance, up to 100kb, the lower average r2 was observed in SOK (0.09) and SZTUM (0.10) breeds, representing draft horse type, and the highest average r2 was observed in AR (0.19) and MLP (0.17) breeds, representing light horse type. At a distance of 4-5Mb, the average values of r2 were 0.03 for HC and KN, 0.02 for AR and MLP and 0.01 for SOK and SZTUM. About 100 generations ago, effective population size (Ne) ranged from 518 (SOK) to 310 (AR) and five generations ago from 85 (SOK) to 40 (HC). A total of 6,162 (AR), 5,792 (MLP), 5,744 (HC), 5,429 (KN), 5,542 (SOK) and 4,848 (SZTUM) haplotype block structures, spanning 656.2Mb (AR), 439.4Mb (MLP), 381.2Mb (HC), 344.3 (KN), 206.7 (SOK) and 171.0Mb (SZTUM) of the genome were detected. Mean block lengths were estimated as 106.5±138kb, 75.9±120kb, 66.4±109kb, 63.4±109kb, 37.3±80kb and 35.3±81kb for AR, MLP, HC, KN, SOK and SZTUM, respectively. A visible similarity in the decay of LD across the genome, as well as in trends of historical Ne, were found for breeds representing the same horse type. Differences in the span of haplotype block structures were found between AR and Polish native horse breeds, which may reflect different demographic population histories and differences in intensity of selection.