Modern Horse Research Articles

The origin and domestication history of domestic horses and the domestication characteristics of breeds.

The horse (Equus caballus) was domesticated thousands of years after dog, cattle, pig, sheep, and goat. Importantly, it represents the domestic animal that mostly impacted the development of human civilization. Its excellent loading and moving ability prompted the changes from fixed farming mode into mobile sharing mode. Accordingly, its domestication history deserves considerable attention. So far, many issues have long been controversial, due to the extinction of the closest wild relatives and the dramatic reduction of genetic diversity. With the continuous development of sequencing technology and the utilization of ancient samples, we got more clues to the origin and domestication process. In this review, we summarize 1) current progresses on the domestication history revealed by nuclear genes, mtDNA, Y chromosome, and ancient DNA, 2) the characteristics of population structure and diversification among modern breeds, 3) the genetic basis of important phenotypes, such as coat color, speed, and body size. The overall aim of the review is to provide in-depth insights into the studies of horse domestication, the preservation and utilization of genetic resources, the direction of breeding improvement, and the development of modern horse industry in future.

Modern methods of research of reproductive organs of mares in pedigree horse breeding

The most important aspect of herd reproduction in horse breeding is the quality of the breeding nucleus of the breeding stock. Currently, the system of domestic comprehensive reproductive evaluation includes five main methods such as rectal, ultrasound, vaginal, cytological and bacteriological studies of the genital tract of mares, which precede visual examination of the external genitalia and the collection of information about the reproductive history of the mare. The purpose of the work is to give an overview and description of the methods of comprehensive evaluation of the reproductive status of mares, which are used in modern pedigree horse breeding. The methods of reproductive evaluation of mares, gives the main advantages of each method and their predictive value when used comprehensively to increase the level of reproduction in the industry have been described in the article. It has been carried out that a complete reproductive evaluation of mares is necessary in rare and complex cases. However, the use of methods of rectal, vaginoscopic, ultrasound, cytological and bacteriological diagnostics of the genital tract of mares is quite within the power of veterinarians and breeding specialists and they are available under production conditions. Their application requires skills in the technical side of the issue and the established system for the prompt dispatch of biomaterial to the nearest, but reliable veterinary or medical bacteriological laboratory. It is well known that even in small horse breeding farms of the Russian Federation, there are currently means and opportunities for the qualitative evaluation of the reproductive system of mares.

A single-nucleotide mutation within the TBX3 enhancer increased body size in Chinese horses

SummaryChinese ponies are endemic to the mountainous areas of southwestern China and were first reported in the archaeological record at the Royal Tomb of Zhongshan King, Mancheng, dated to approximately ∼2,100 YBP.1 Previous work has started uncovering the genetic basis of size variation in western ponies and horses, revealing a limited number of loci, including HMGA2,2LCORL/NCAPG,3ZFAT, and LASP1.4,5 Whether the same genetic pathways also drive the small body size of Chinese ponies, which show striking anatomical differences to Shetland ponies,6 remains unclear.2,7 To test this, we combined whole-genome sequences of 187 horses across China. Statistical analyses revealed top association between genetic variation at the T-box transcription factor 3 (TBX3) and the body size. Fine-scale analysis across an extended population of 189 ponies and 574 horses narrowed down the association to one A/G SNP at an enhancer region upstream of the TBX3 (ECA8:20,644,555, p = 2.34e−39). Luciferase assays confirmed the single-nucleotide G mutation upregulating TBX3 expression, and enhancer-knockout mice exhibited shorter limbs than wild-type littermates (p < 0.01). Re-analysis of ancient DNA data showed that the G allele, which is most frequent in modern horses, first occurred some ∼2,300 years ago and rose in frequency since. This supports selection for larger size in Asia from approximately the beginning of the Chinese Empire. Overall, this study characterized the causal regulatory mutation underlying small body size in Chinese ponies and revealed size as one of the main selection targets of past Chinese breeders.

THE CURRENT STATE OF THE POLESIE HORSE POPULATION AND THE TARGET STANDARD OF THE MAIN TRAITS OF ITS CONFORMATION

THE CURRENT STATE OF THE POLESIE HORSE POPULATION AND THE TARGET STANDARD OF THE MAIN TRAITS OF ITS CONFORMATION

THE EFFECTIVENESS OF THE USE OF VARIOUS ISSR-MARKERS IN THE STUDY OF HORSES

The article presents the results of molecular genetic studies performed on samples of biological material from ancient horses (DNA was isolated from fossils of Pleistocene horse and tarpan) and three aboriginal breeds of modern horses (Polish horse, Hutsul breed, Arabian breed). The research was conducted in the laboratory of genetics IRGT. M.V.Zubets NAAS. Purpose of research. This work was carried out to compare the effectiveness of each of the ISSR-markers and then select the optimal combination in the study of polymorphism of the genetic structure of horses To study the DNA polymorphism of horses on ISSR markers, we used eight primers that are considered the most informative (AG)8CA, (AG)9C, (GA)6CC, (GA)9C, (AG)8CG, (GAG)6C, (ACC)6G, (CTC)6C.&#x0D; Research methods. DNA from the blood was isolated using a set of reagents "DNA sorb B". From fossil remains of horses, DNA was isolated by an optimized method using proteinase K and dithiothreitol. The PCR mixture contained: 1 μl of buffer for Tag polymerase, 1 μl of a mixture of triphosphates ("Amplisens", RF), 0.8 μl of the appropriate primer, 0.2 μl of DNA polymerase ("Fermentas", Lithuania), water for PCR 3 μl. Genomic DNA was added in an amount of 4 μl. The total volume of the DNA mixture was 10 μl. Amplification was performed on a programmed four-channel thermocycle "Tertsyk" ("DNA technology", Russia). The amplification program included primary denaturation (95°C, 2 min); 30 cycles of denaturation (95°C, 30 s), hybridization of primers (54–64°C, 30 s) and elongation (72°C, 1 min), finishing elongation (72°C, 5 min).&#x0D; To more accurately estimate the lengths of the detected amplification fragments, a universal scale was used, where the gradation of DNA fragments by molecular weights was used. Depending on the zone ("heavy", "medium" and "light" fragments), a certain step from 10 to 200 bp was used. As a result, 38 zones with a fixed interval were identified, which allow to accurately determine the molecular weight for amplification products of different lengths and standardize the results of this study.&#x0D; Obtained results and conclusions. In the study of the obtained spectra of amplification products, we found that the largest number of loci was obtained by using as primers the sequences (GA) 6CC and (GAG) 6C – 9 and 8 loci. At the same time, primers (AG) 8CA – 0.27, (AG) 9C – 0.21 and (ACC) 6G – 0.21 were the most polymorphic in terms of PIC. It should be noted that when using primer (GA) 6CC in the study of genetic polymorphism of horses was obtained a significant range of amplification products – 9 loci, with a polymorphism index of 0.16, which allows it to be used quite effectively for research. Using the sequence (AG) 8CG was characterized by the lowest PIC index and was 0.02. As a result, we found that the most effective for the detection of polymorphism in the PIC index in horses was the use of primers sequences (AG) 8CA, (AG) 9C, and (ACC) 6G. To obtain the largest range of amplification fragments in horses by ISSR-PCR, the most effective was the use of the sequence (GA) 6CC and (GAG) 6C.

Ancient DNA points to origins of modern domestic horses

Genetic analysis shows that the ancestors of all modern horses lived in the Western Eurasian steppes more than 4,000 years ago. Genetic analysis shows that the ancestors of all modern horses lived in the Western Eurasian steppes more than 4,000 years ago.

Ancient DNA reveals long-sought homeland of modern horses.

Bronze Age herders began riding the ancestor of modern horses in the grassy western Eurasian steppe

Modern horses emerged from Western Eurasia

Modern horses emerged from Western Eurasia

202 Nature versus the NRC: Utilizing an Understanding of the “natural” Diet of the Horse in Contrast to Defined Guidelines

Abstract A comprehensive look at nutrients available in nature compared to equine nutrient requirements and the modern diets we feed them. Horses can survive on a variety of feedstuffs that they ingest if they are relatively equine-specific and the horses’ forage requirements are met for basic gastrointestinal health. It is safe to say that some horses in the United States continue to be fed as “nature-intended” with 24/7 access to fresh pasture or adequate plant material and enough room to continually move and graze. Many other horses, however, have only limited or no access to pasture and their movement is greatly restricted via stall confinement or small areas to move. In addition, there is a wide variety in what we ask horses to do, from horses that are simply pasture pets, to horses performing as elite-level athletes in racing and competitions. And when we look at all these factors from a nutrition perspective, how do the nutrients provided by nature match up with the requirements as set by the National Research Council’s Nutrient Requirements for Horses? And how do these nutrients provided by nature compare to how we are feeding many modern horses today? This presentation will examine these factors and shed light on differences between the NRC nutrient requirements and what is provided by both nature and/or modern feeding practices in several scenarios, to identify areas of mismatch that could be potentially addressed or researched further in an effort to improve the health and well-being of horses.

127 Equine Nutraceuticals: Is Science Finally Catching up to Fiction?

Abstract Nutraceutical supplements have become requisite fare in equine stables across North America and Europe, and a robust marketing engine has propagated the notion that every horse owner has the ability to contribute to the management – and even treatment – of some of the most important health and performance issues facing the modern horse. The voracious appetite of horse owners and managers for these supplements has vastly outpaced research into equine-specific efficacy, safety or toxicity of the majority of available products. Indeed, even government regulators have been left scrambling to accommodate the unique characteristics of nutraceuticals for horses within existing feed and drug guidelines, whilst the groundswell of consumer demand creates a fertile and attractive venue for a myriad of equine nutraceutical products. This presentation will identify peculiarities of horses and horse enthusiasts which define the opportunities and challenges associated with equine nutraceutical products. The current state of scientific inquiry will be explored, focusing on supplements targeting common equine health issues including arthritis, laminitis and gastrointestinal disorders. This critical mass of scientific evidence is then compared with popular marketing of equine nutraceuticals, in order to caliper the distance between science and fiction.

Sequence analysis of the mitochondrial D-loop region throws a new light on the origin of Hungarian Nonius, Danubian Horse and Serbian Nonius.

The objective of our study was to investigate the genetic structure of yet uninvestigated populations of three closely related horse breeds - the Danubian Horse, the Hungarian Nonius and the Serbian Nonius - in order to clarify their origin and genetic diversity. A 640-bp-long fragment of the mtDNA D-loop region was amplified and sequenced. The results showed that the investigated breeds have different genetic profiles although they share some common characteristics. We identified nine of the 17 haplogroups described in modern horses. Most of the obtained sequences fall into the M, L, G, and O'P lineages, which is indicative of the genetic profile of the ancestral mares that had probably been used at the initial stages of the formation of the breeds. The population of the Danubian Horse is characterised by a high prevalence of the Anatolian specific haplogroup G (45%), followed by the Western Eurasian specific haplogroups L and M (both about 21%). In the Hungarian Nonius breed we found the highest frequency of the Western Eurasian haplogroup M (44%), followed by the Middle Eastern O'P (26%) and the Central Asian specific E (13%) and G (13%). The Serbian Nonius showed a distinct genetic profile, characterised by a high prevalence of the rare European haplogroup D (67%), followed by the Central Asian specific haplogroup G (17%). The high percentage of haplogroups shared especially between the Danubian and the Hungarian Nonius indicates the possibility of a common origin of the two breeds. In contrast, the Serbian Nonius showed a specific genetic profile, which can be explained by a different and independent origin.

Resilience of Faecal Microbiota in Stabled Thoroughbred Horses Following Abrupt Dietary Transition between Freshly Cut Pasture and Three Forage-Based Diets.

Simple SummaryAbrupt changes in the dietary management of horses are a risk factor for gastrointestinal disturbances, potentially due to the negative effects observed on the population of gut microbiota. In this study, the faecal microbiota of horses was investigated to determine how quickly the bacterial communities respond and stabilise following sudden diet change. Six Thoroughbred mares were stabled for six weeks, consuming freshly cut pasture (on weeks 1, 3 and 5), before being abruptly fed three conserved forage-based diets (weeks 2, 4 and 6). The conserved forage-based diets were a chopped ensiled forage fed exclusively or with whole oats, and perennial ryegrass hay fed with whole oats. Faecal samples were collected at regular intervals from each horse following each diet change. High throughput 16S rRNA gene sequencing was used to evaluate the faecal microbiota. There were significant differences in the diversity of the microbiota (p < 0.001), with clustering of samples observed by diet group. A stable faecal microbiota profile was observed in the samples from 96 h after consumption of the treatment diets containing ensiled chopped forage. The present study confirmed that the diversity and community structure of the faecal bacteria in horses is diet-specific and resilient following dietary transition and emphasised the need for modern horse feeding management to incorporate large proportions of forage into diets.The management of competition horses in New Zealand often involves rotations of short periods of stall confinement and concentrate feeding, with periods of time at pasture. Under these systems, horses may undergo abrupt dietary changes, with the incorporation of grains or concentrate feeds to the diet to meet performance needs, or sudden changes in the type of forage fed in response to a lack of fresh or conserved forage. Abrupt changes in dietary management are a risk factor for gastrointestinal (GI) disturbances, potentially due to the negative effects observed on the population of GI microbiota. In the present study, the faecal microbiota of horses was investigated to determine how quickly the bacterial communities; (1) responded to dietary change, and (2) stabilised following abrupt dietary transition. Six Thoroughbred mares were stabled for six weeks, consuming freshly cut pasture (weeks 1, 3 and 5), before being abruptly transitioned to conserved forage-based diets, both offered ad libitum. Intestinal markers were administered to measure digesta transit time immediately before each diet change. The conserved forage-based diets were fed according to a 3 × 3 Latin square design (weeks 2, 4 and 6), and comprised a chopped ensiled forage fed exclusively (Diet FE) or with whole oats (Diet FE + O), and perennial ryegrass hay fed with whole oats (Diet H + O). Faecal samples were collected at regular intervals from each horse following the diet changes. High throughput 16S rRNA gene sequencing was used to evaluate the faecal microbiota. There were significant differences in alpha diversity across diets (p < 0.001), and a significant effect of diet on the beta diversity (ANOSIM, p = 0.001), with clustering of samples observed by diet group. There were differences in the bacterial phyla across diets (p < 0.003), with the highest relative abundances observed for Firmicutes (62–64%) in the two diets containing chopped ensiled forage, Bacteroidetes (32–38%) in the pasture diets, and Spirochaetes (17%) in the diet containing hay. Major changes in relative abundances of faecal bacteria appeared to correspond with the cumulative percentage of intestinal markers retrieved in the faeces as the increasing amounts of digesta from each new diet transited the animals. A stable faecal microbiota profile was observed in the samples from 96 h after abrupt transition to the treatment diets containing ensiled chopped forage. The present study confirmed that the diversity and community structure of the faecal bacteria in horses is diet-specific and resilient following dietary transition and emphasised the need to have modern horse feeding management that reflects the ecological niche, particularly by incorporating large proportions of forage into equine diets.

Determining the gait of Miocene, Pliocene, and Pleistocene horses from fossilized trackways

Abstract. Much work has been done on the study of vertebrate gaits over the past several decades and efforts undertaken to apply this to fossil tracks, especially dinosaurs and mammals such as cats, dogs, camels, and horses. This work seeks to expand upon such studies and in particular to study footprints laid down in sand by modern horses and apply such studies to determine the gaits of fossil horse trackways. It thus builds upon the work of Renders (1984a, b) and Kienapfel et al. (2014) and suggests additional measurements that can be taken on horse footprints. In this study the footprints left in the sand by 15 horses of various breeds with various gaits were videotaped, photographed, described, and measured in order to determine characteristics useful in distinguishing gaits. These results were then applied to two new sets of fossil footprints, those of the middle Miocene merychippine horse Scaphohippus intermontanus that I personally examined and measured and those from the late Pleistocene horse Equus conversidens, previously illustrated and described in the literature (McNeil et al., 2007). The latter horse exhibits a fast gallop of around 9.4 m/s, but it is the former whose footprints are quite unique. The quantitative and visual features of these prints are suggestive of a medium-fast gait involving apparent “understepping” of diagonal couplets and hind feet that overlap the centerline. The gait that most closely matches the footprints of Scaphohippus is the “artificial” gait of a slow rack or tölt, or pace, around 1.9 m/s, though an atypical trot of a horse with major conformation issues or which is weaving (swaying) from side to side is a less likely possibility. This intimates, along with the earlier study of Renders (1984a, b), who found the artificial gait of the running walk displayed by Pliocene hipparionine horses, that ancient horses possessed a much greater variety of gaits than modern horses and that over time they lost these abilities with the exception of certain gaited breeds.

A comparative analysis of the intrauterine transcriptome in fertile and subfertile mares using cytobrush sampling

BackgroundSubfertility is a major problem in modern horse breeding. Especially, mares without clinical signs of reproductive diseases, without known uterine pathogens and no evidence of inflammation but not becoming pregnant after several breeding attempts are challenging for veterinarians. To obtain new insights into the cause of these fertility problems and aiming at improving diagnosis of subfertile mares, a comparative analysis of the intrauterine transcriptome in subfertile and fertile mares was performed. Uterine cytobrush samples were collected during estrus from 57 mares without clinical signs of uterine diseases. RNA was extracted from the cytobrush samples and samples from 11 selected subfertile and 11 fertile mares were used for Illumina RNA-sequencing.ResultsThe cytobrush sampling was a suitable technique to isolate enough RNA of high quality for transcriptome analysis. Comparing subfertile and fertile mares, 114 differentially expressed genes (FDR = 10%) were identified. Metascape enrichment analysis revealed that genes with lower mRNA levels in subfertile mares were related to ‘extracellular matrix (ECM)’, ‘ECM-receptor interaction’, ‘focal adhesion’, ‘immune response’ and ‘cytosolic calcium ion concentration’, while DEGs with higher levels in subfertile mares were enriched for ‘monocarboxyl acid transmembrane transport activity’ and ‘protein targeting’.ConclusionOur study revealed significant differences in the uterine transcriptome between fertile and subfertile mares and provides leads for potential uterine molecular biomarkers of subfertility in the mare.

Traces of Late Bronze and Early Iron Age Mongolian Horse Mitochondrial Lineages in Modern Populations.

The Mongolian horse is one of the most ancient and relatively unmanaged horse breeds. The population history of the Mongolian horse remains poorly understood due to a lack of information on ancient and modern DNA. Here, we report nearly complete mitochondrial genome data obtained from five ancient Mongolian horse samples of the Khereksur and Deer Stone culture (late 2nd to 1st third of the 1st millennium BC) and one ancient horse specimen from the Xiongnu culture (1st century BC to 1st century AD) using target enrichment and high-throughput sequencing methods. Phylogenetic analysis involving ancient, historical, and modern mitogenomes of horses from Mongolia and other regions showed the presence of three mitochondrial haplogroups in the ancient Mongolian horse populations studied here and similar haplotype composition of ancient and modern horse populations of Mongolia. Our results revealed genetic continuity between the Mongolian horse populations of the Khereksur and Deer Stone culture and those of the Xiongnu culture owing to the presence of related mitotypes. Besides, we report close phylogenetic relationships between haplotypes of the Khereksur and Deer Stone horses and the horses of indigenous breeds of the Middle East (Caspian and Iranian), China (Naqu, Yunnan, and Jinjiang), and Italy (Giara) as well as genetic similarity between the Xiongnu Mongolian horses and those of the most ancient breeds of the Middle East (Arabian) and Central Asia (Akhal-Teke). Despite all the migrations of the Mongolian peoples over the past 3000 years, mitochondrial haplogroup composition of Mongolian horse populations remains almost unchanged.

The Evolutionary and Historical Foundation of the Modern Horse: Lessons from Ancient Genomics.

The domestication of the horse some 5,500 years ago followed those of dogs, sheep, goats, cattle, and pigs by ∼2,500-10,000 years. By providing fast transportation and transforming warfare, the horse had an impact on human history with no equivalent in the animal kingdom. Even though the equine sport industry has considerable economic value today, the evolutionary history underlying the emergence of the modern domestic horse remains contentious. In the last decade, novel sequencing technologies have revolutionized our capacity to sequence the complete genome of organisms, including from archaeological remains. Applied to horses, these technologies have provided unprecedented levels of information and have considerably changed models of horse domestication. This review illustrates how ancient DNA, especially ancient genomes, has inspired researchers to rethink the process by which horses were first domesticated and then diversified into a variety of breeds showing a range of traits that are useful to humans.

Commercial genetic testing for type 2 polysaccharide storage myopathy and myofibrillar myopathy does not correspond to a histopathological diagnosis.

BackgroundCommercial genetic tests for type 2 polysaccharide storage myopathy (PSSM2) and myofibrillar myopathy (MFM) have not been validated by peer‐review, and formal regulation of veterinary genetic testing is lacking.ObjectivesTo compare genotype and allele frequencies of commercial test variants (P variants) in MYOT (P2; rs1138656462), FLNC (P3a; rs1139799323), FLNC (P3b; rs1142918816) and MYOZ3 (P4; rs1142544043) between Warmblood (WB) and Arabian (AR) horses diagnosed with PSSM2/MFM by muscle histopathology, and phenotyped breed‐matched controls. To quantify variant frequency in public repositories of ancient and modern horse breeds.Study designCross sectional using archived clinical material and publicly available data.MethodsWe studied 54 control‐WB, 68 PSSM2/MFM‐WB, 30 control‐AR, 30 PSSM2/MFM‐AR and 205 public genotypes. Variants were genotyped by pyrosequencing archived DNA. Genotype and allele frequency, and number of variant alleles or loci were compared within breed between controls, PSSM2/MFM combined and MFM or PSSM2 horses considered separately using additive/genotypic and dominant models (Fisher's exact tests). Variant frequencies in modern, early domestic and Przewalski horses were determined from a public data repository.ResultsThere was no significant association between any P locus and a histopathological diagnosis of PSSM2/MFM, and no difference between control and myopathic horses in total loci with alternative alleles, or total alternate alleles when PSSM2/MFM was considered combined or separately as PSSM2 or MFM. For all tests, sensitivity was <0.33. Allele frequencies in WB (controls/cases) were: 8%/15% (P2), 5%/6% (P3a/b) and 9%/13% (P4); in AR, frequencies were: 12%/17% (P2), 2%/2% (P3a/b) and 7%/12% (P4). All P variants were present in early domestic (400‐ to 5500‐year‐old) horses and P2 present in the Przewalski.ConclusionsBecause of the lack of significant association between a histopathological diagnosis of PSSM2 or MFM and the commercial genetic test variants P2, P3 and P4 in WB and AR, we cannot recommend the use of these variant genotypes for selection and breeding, prepurchase examination or diagnosis of a myopathy.

New specimens of anchitheriine from the Linxia Basin, Gansu and evolution of East Asian anchitheriines

Anchitheriinae are an extinct subfamily of the Perissodactyla family Equidae, the same family which includes modern horses, zebras and donkeys. Anchitheriinae are the most poorly studied of the Equidae. The distribution of anchitheriines in China has been recorded in Shanxi, Gansu, Inner Mongolia, Xinjiang, Hubei and Jiangsu in the early to middle, and the latest Miocene. Recently, some specimens of Anchitheriine have also been found in the Linxia Basin, Gansu. A specimen from the Wangjiashan locality was found to be a large-sized individual with complex morphology characteristic. The specimen was identical to the reported material of Sinohippus robustus from the same locality. Both specimens were very large size, had a distobuccal crest on the labial wall of p2, and displayed a deep and narrow ectoflexid perpendicular to major axis of the tooth. Based on these observations, the new specimen was identified as S. robustus . Specimens from the Laogou locality have been identified as Anchitherium gobiense in brief reports of the local fauna. Identification of the specimens was confirmed based on the complexity of diagnostic feature complexity such as medium size and characteristics of the lower cheek tooth row that progressively reduced from the middle to the ends. A detailed morphological analysis of these samples was performed on East Asian anchitheriines and compared to specimens from China and Japan. These observations confirmed a previous hypothesis that “ Anchitherium aurelianense ” from Fangshan, Nanjing, were more similar to Anchitherium gobiense , and should be considered as a different lineage from the true Anchitherium aurelianense found in Europe. The specimen from Fangxian, Hubei, was identified as Anchitherium gobiense from a previous research study. However, the size of the specimen was significantly larger than the Xinjiang specimens, and the holotype and the paratype specimens from Tunggur of Inner Mongolia. Two forms with obviously different sizes were also observed amongst the Tunggur specimens. The Fangxian specimen, and the larger from Tunggur were temporally attributed as Anchitherium gobiense type B. Based on morphological differences, Anchitherium aff. gobiense from the Kani Basin, Japan, are different from true Anchitherium gobiense and other forms found in Eurasia and considered to be Anchitherium hypohippoides in the present paper. The Japanese form has a less concave labial wall on the upper cheek tooth, which is a very primitive feature usually seen in ancestral forms found in North America, such as genus Kalobatippus. Eurasian anchitheriines were derived from North American Kalobatippus , and rapidly separated into the European and East Asian clades after they dispersed into Eurasia. The Japanese species Anchitherium hypohippoides, is the most primitive form, and different evolutionary stages were present in the Chinese clade over time. These stages are represented by “ A. aurelianense ” of Fangshan, A. gobiense group (including A. gobiense s. s. and Type B) and Sinohippus . Large species derived from Sinohippus occurred suddenly in China in the latest Miocene, showed gaps in both chronological and morphological transition. The origin of Sinohippus is unclear, but is a likely relative to a large form of Anchitherium sampelayoi in Europe. The first occurrence of latter come from Spain in about 11 Ma. An evolutionary trend was present in the East Asian anchitheriine clade, in which the body size of anchitheriines was firstly reduced and then increased. This is a normal phenomenon in Eurasian Equidea, such as Hipparion and Equus , and correlated to the demand of the animal itself for immigration, and the pattern of change in the climate and environment. Transcontinental immigration often depends on the connection of land bridges caused by drops in the sea level which eventually occur as a result of climate cooling. Large body size is advantageous in having resistance to cold and allows very long-distance immigration. In contrast, reduced body size can help to avoid fierce competition against other forms in similar niches and often results from warmer climates and increased richness of the community. With further improvement in the environment, the body size of anchitheriines may increase due to the improved availability of resources.

Modern Northern Domestic Horses Carry Mitochondrial DNA Similar to Przewalski\u2019s Horse

Several recent studies have suggested past gene flow between the Przewalski’s horse and modern domestic horse and questioned the wild origin of the Przewalski’s horse. Mitochondrial DNA has placed representatives of the Przewalski’s horse into three among the eighteen haplogroups detected from the modern horse. Of these, two haplogroups have so far been found exclusively in the Przewalski’s horse, while the one shared with the domestic horse includes captive individuals that have uncertain pedigrees. We recently found five domestic horse individuals of North European horse breeds to carry a mitochondrial haplogroup that was previously confined only to the Przewalski’s horse. These individuals were sequenced for 6039 bp of mitochondrial DNA and used, together with domestic and Przewalski’s horse sequences presenting all horse haplogroups, to examine the phylogenetic relationships and to date the divergence time between Przewalski’s and domestic horse clusters within this haplogroup. The divergence was dated to have likely occurred about 13,300–11,400 years ago, which coincides with the time of the Younger Dryas.

A genome-wide signatures of selection study of Welsh ponies and draft horses revealed five genes associated with horse type variation

The modern horse populations with diverse types have been shaped through evolutionary forces, domestication, and recent breeding programs. Horse breeds are grouped into pony, light, and draft, mainly based on their body morphology. Identifying the selection pressure patterns on the genome level can improve our knowledge of evolution of horse types. The genome-wide single nucleotide polymorphisms of 42 Welsh ponies and 38 draft horses were used to detect selection signals by employing Z-transformed of fixation index (Z(Fst)) and extended haplotype homozygosity (xp-EHH). Our findings revealed a total number of 549 genes as signatures of selection out of which five were observed in both methods. These genes are known as candidate genes for osteolysis (SRCIN), growth (LAP3), and morphological traits including body size (LCORL and ZFAT), hock circumference and body length (FAM184B). A gene enrichment analysis based on these identified genes revealed two significant biological processes: macromolecule metabolic process (GO:0043170) and nitrogen compound metabolic process (GO:0006807), which might be related to regulation of skeletal muscle growth, and bone formation in horses. These results can help us to better understand the genetic background of evolving type and body morphology of draft horses, and ponies. Additionally, our findings in this study might be helpful to develop the SNP panels for future genomic selection programs in horses.