Genetic analysis of seven Italian horse breeds based on mitochondrial DNA D-loop variation

Mitochondrial DNA D-loop hyper-variable region 1 variability in Kurdish horse breed

BACKGROUND

Kurdish horse is one of the most valuable horse genetic resources in the Middle East.

OBJECTIVES

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.

METHODS

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 294 bp 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.

RESULTS

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).

CONCLUSIONS

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.

Вариабельность последовательности D-петли митохондриальной ДНК у лошадей забайкальской породы

The Zabaikalskaya horse is an indigenous breed of horses from Siberia with diverse use. It is characterized by endurance and good adaptability to year-round herd maintenance in the harsh conditions of the Baikal steppes. To determine the genetic characteristics of the maternal lineage of the Zabaikalskaya horse breed based on mitochondrial DNA polymorphisms, we collected hair samples from 31 horses belonging to breeding farms in the Trans-Baikal Territory. Analysis of the 530 bp sequence of the mtDNA D-loop was performed using the maximum composite likelihood (MCL) model in combination with bootstrap analysis. When studying the polymorphism of the hypervariable region of the mtDNA D- loop in Zabaikalskaya horses, we identif ied 31 haplotypes representing 8 haplogroups: B, C, G, H, L, M, Q and R according to modern classif ication. The sequenced fragment of the D-loop from nucleotide position 15471 to 16000 contained 17 polymorphic sites, mainly represented by the A→G, G→A and T→C transitions. The haplogroups Q (25.81 %), B (19.35 %), G (16.13 %) and H (12.90 %) were prevailing in the mtDNA structure of this breed. Genetic analysis of the mitochondrial genome of the Zabaikalskaya horse revealed a high level of diversity of haplotypes and haplogroups, which are typical for the horse populations of Eurasia.

Variability analyses of the maternal lineage of horses and donkeys

Equid breeds originating from the Iberian Peninsula and North Africa are believed to have genetically contributed to the formation of breeds and ecotypes from Brazil. The country has numerous breeds and ecotypes of horses and donkeys but there are no extensive studies on maternal genetic diversity and their origins. This study reports the results of the first genetic analysis of all horse and donkey breeds/ecotypes from Brazil based on sequences of the mitochondrial DNA control region (D-loop) whose main objective was to characterize the genetic variation in these animals. These analyses will contribute to the understanding of the current population structure and diversity of breeds/ecotypes of horses and donkeys raised in the Brazil. We analyzed 310 D-loop sequences representing 41 breeds/ecotypes of Equus caballus and Equus asinus, including 14 native horse breeds/ecotypes, 3 native donkey breeds/ecotypes and 24 cosmopolite horse breeds. The results revealed that the breeds are well structured genetically and that they comprise different groups. A total of 80 and 14 haplotypes were identified for horses and donkeys, respectively. Most of the horse mtDNA haplotypes were shared by many breeds, whereas donkey mtDNA haplotypes seemed to be more group-especif. Some groups presented a low intrabreed distance and/or a low haplotype/nucleotide diversity such as Lavradeiro, Crioulo, Piquira and Percheron horses and Brazilian donkey. Thus, specific actions must be designed for each population. The different levels of genetic diversity provided important information for conservation resource management of adapted groups as well as for mating orientation of breed associations. Some autochthonous ecotypes require attention because of their low genetic variability.

Mitochondrial DNA variation in the Italian Heavy Draught Horse

Background

In the last decades, Italy as well as other developed countries have registered a decrease in the population size of many local horse breeds. The continuous crossbreeding has determined the dilution of genetic heritage of several native breeds. The Italian Heavy Draught Horse (IHD) is the only autochthonous Italian coldblooded horse among these breeds; therefore, it represents a resource to be preserved. In 1927, the first generation of this breed was officially created by crossing different Heavy Draught horses with local mares and recorded in a Studbook.

Methodology

To provide the first comprehensive overview of the genetic diversity of Italian Heavy Draught horses from Central Italy, we produced and phylogenetically analysed 52 mitochondrial DNA (mtDNA) control-region sequences. Furthermore, we evaluated data available from GenBank (N = 568) to have a more complete scenario and to understand the relationships with other European Heavy Draught horse breeds.

Results

Among the IHD samples that were analysed, we identified ten of the 17 haplogroups described in modern horses. Most of these sequences fell into L, G, and M lineages, thus showing the overall mtDNA legacy of the ancestral mares that were probably used at the initial stages of breeding selections a long time ago. The high mitochondrial haplotype diversity (Hd = 0.969) found in our samples reflected the multiple maternal origins of the horses. Our results highlighted a considerable percentage of haplotypes shared especially with Bardigiano and Hungarian Heavy Draught breeds. Furthermore, both the presence of four unique haplotypes detected in our samples and their absence among all equine mitochondrial published data demonstrate a mitochondrial peculiarity that needs to be further investigated and preserved with careful breeding practices.

Abundant genetic diversity and maternal origins of modern horses

To clarify the origin and genetic diversity of modern horses, mitochondrial DNA (mtDNA) D-loop sequences were generated for 3965 horses from 12 geographical regions. From these sequences, we observed 439 haplotypes defined by 138 polymorphic nucleotide sites. All horses were genetically diverse (HD = 0.973 ± 0.001, π = 0.0243 ± 0.0005), which showed that maternal lineages of the domestic horse are worldwide highly diverse. In general, all 18 haplogroups were presented in the Asian horse. The majority of modern horse sequences belong to haplogroups L, Q, and A. At the same time, 194 archaeological samples from four geographical regions were obtained. Indeed, haplogroup distributions are overlapping in modern and ancient samples, indicating that most haplogroups were already present in ancient times at least in Europe and Asia. The network showed that breeds of Asian and Europe regions overlapped, suggesting that extensive gene flow had occurred between different horse breeds in Asian and European regions.

Genetic Diversity and Structure of Iranian Horses' Population Based on Mitochondrial Markers

The source and history of horse domestication have been studied for decades in biology and archeology. The aim of this study was to evaluate the genetic structure and the genetic relationship between six breeds of native horses using mitochondrial D-loop region. Blood samples were collected from 96 horses. Total DNA was extracted, and 430 bp of D-Loop region (hyper variable) was amplified and sequenced using Sanger sequencing methods. The analysis of data led to identify 48 polymorphic sites that create 52 haplotypes. The plotted phylogenic tree for haplotypes of Iranian native horses is placed in the 11 haplogroups including A, B, C, E, G, I, L, M, N, P, and Q. Genetic and haplotype diversity values obtained were 0.0233 and 0.980, respectively. Nucleotide diversity (Pi) was observed between 0.0172 and 0.0242 in populations. In addition, the average number of nucleotide differences (k) ranged from 6.0 (Darehshori or Qashqai horse [DAH]) to 8.5 (Kord horse [KOH]) with an average value of 7.8. The highest and lowest genetic differentiates were observed between KOH and DAH (Fst = 0.193) and between North West native horse and horse riding club in North West (Fst = 0.003), respectively. Tajima D of 0.441 was obtained for all samples which was not significant (P > .01). The results indicate high genetic variety and numerous maternal lines in native horses of Iran.

Genetic analysis of maternal and paternal lineages in Kabardian horses by uniparental molecular markers

Studies of mitochondrial DNA (mtDNA) as well as the non-recombining part of the Y chromosome help to understand the origin and distribution of maternal and paternal lineages. The Kabardian horse from Northern Caucasia which is well-known for strength, stamina and endurance in distance riding has a large gap in its breeding documentation especially in the recent past. A 309 bp fragment of the mitochondrial D-loop (156 Kabardian horses) and six mutations in Y chromosome (49 Kabardian stallions), respectively, were analyzed to get a better insight into breeding history, phylogenetic relationship to related breeds, maternal and paternal diversity and genetic structure. We found a high mitochondrial diversity represented by 64 D-loop haplotypes out of 14 haplogroups. The most frequent haplogroups were G (19.5%), L (12.3%), Q (11.7%), and B (11.0%). Although these four haplogroups are also frequently found in Asian riding horses (e.g. Buryat, Kirghiz, Mongolian, Transbaikalian, Tuvinian) the percentage of the particular haplogroups varies sometimes remarkable. In contrast, the obtained haplogroup pattern from Kabardian horse was more similar to that of breeds reared in the Middle East. No specific haplotype cluster was observed in the phylogenetic tree for Kabardian horses. On Kabardian Y chromosome, two mutations were found leading to three haplotypes with a percentage of 36.7% (haplotype HT1), 38.8% (haplotype HT2) and 24.5% (haplotype HT3), respectively. The high mitochondrial and also remarkable paternal diversity of the Kabardian horse is caused by its long history with a widely spread maternal origin and the introduction of Arabian as well as Thoroughbred influenced stallions for improvement. This high genetic diversity provides a good situation for the ongoing breed development and performance selection as well as avoiding inbreeding.

D-loop haplotype diversity in Brazilian horse breeds

The first horses were brought to Brazil by the colonizers after 1534. Over the centuries, these animals evolved and adapted to local environmental conditions usually unsuitable for exotic breeds, thereby originating locally adapted Brazilian breeds. The present work represents the first description of maternal genetic diversity in these horse breeds based on D-loop sequences. A D-Loop HSV-I fragment of 252 bp, from 141 horses belonging to ten Brazilian breeds / genetic groups (locally adapted and specialized breeds) were analysed. Thirty-five different haplotypes belonging to 18 haplogroups were identified with 33 polymorphic sites. Haplotype diversity (varying from 0.20 to 0.96) and nucleotide diversity (varying from 0.0039 to 0.0239) was lower for locally adapted than for specialized breeds, with the same pattern observed for F_ST values. Haplogroups identified in Brazilian breeds are in agreement with previous findings in South American samples. The low variability observed mainly in locally adapted breeds, indicates that, to ensure conservation of these breeds, careful reproductive management is needed. Additional genetic characterization studies are required to support accurate decision-making.

Characterization of the Polish Primitive Horse (Konik) maternal lines using mitochondrial D-loop sequence variation

The Polish Primitive Horse (PPH, Konik) is a Polish native horse breed managed through a conservation program mainly due to its characteristic phenotype of a primitive horse. One of the most important goals of PPH breeding strategy is the preservation and equal development of all existing maternal lines. However, until now there was no investigation into the real genetic diversity of 16 recognized PPH dam lines using mtDNA sequence variation. Herein, we describe the phylogenetic relationships between the PPH maternal lines based upon partial mtDNA D-loop sequencing of 173 individuals. Altogether, 19 mtDNA haplotypes were detected in the PPH population. Five haplotypes were putatively novel while the remaining 14 showed the 100% homology with sequences deposited in the GenBank database, represented by both modern and primitive horse breeds. Generally, comparisons found the haplotypes conformed to 10 different recognized mtDNA haplogroups (A, B, E, G, J, M, N, P, Q and R). A multi-breed analysis has indicated the phylogenetic similarity of PPH and other indigenous horse breeds derived from various geographical regions (e.g., Iberian Peninsula, Eastern Europe and Siberia) which may support the hypothesis that within the PPH breed numerous ancestral haplotypes (found all over the world) are still present. Only in the case of five maternal lines (Bona, Dzina I, Geneza, Popielica and Zaza) was the segregation of one specific mtDNA haplotype observed. The 11 remaining lines showed a higher degree of mtDNA haplotype variability (2-5 haplotypes segregating in each line). This study has revealed relatively high maternal genetic diversity in the small, indigenous PPH breed (19 haplotypes, overall HapD = 0.92). However, only some traditionally distinguished maternal lines can be treated as genetically pure. The rest show evidence of numerous mistakes recorded in the official PPH pedigrees. This study has proved the importance of maternal genetic diversity monitoring based upon the application of molecular mtDNA markers and can be useful for proper management of the PPH conservation program in the future.

An Overview of Ten Italian Horse Breeds through Mitochondrial DNA

BACKGROUND

The climatic and cultural diversity of the Italian Peninsula triggered, over time, the development of a great variety of horse breeds, whose origin and history are still unclear. To clarify this issue, analyses on phenotypic traits and genealogical data were recently coupled with molecular screening.

METHODOLOGY

To provide a comprehensive overview of the horse genetic variability in Italy, we produced and phylogenetically analyzed 407 mitochondrial DNA (mtDNA) control-region sequences from ten of the most important Italian riding horse and pony breeds: Bardigiano, Esperia, Giara, Lipizzan, Maremmano, Monterufolino, Murgese, Sarcidano, Sardinian Anglo-Arab, and Tolfetano. A collection of 36 Arabian horses was also evaluated to assess the genetic consequences of their common use for the improvement of some local breeds.

CONCLUSIONS

In Italian horses, all previously described domestic mtDNA haplogroups were detected as well as a high haplotype diversity. These findings indicate that the ancestral local mares harbored an extensive genetic diversity. Moreover, the limited haplotype sharing (11%) with the Arabian horse reveals that its impact on the autochthonous mitochondrial gene pools during the final establishment of pure breeds was marginal, if any. The only significant signs of genetic structure and differentiation were detected in the geographically most isolated contexts (i.e. Monterufolino and Sardinian breeds). Such a geographic effect was also confirmed in a wider breed setting, where the Italian pool stands in an intermediate position together with most of the other Mediterranean stocks. However, some notable exceptions and peculiar genetic proximities lend genetic support to historical theories about the origin of specific Italian breeds.

A genetic analysis of the Italian Salernitano horse

Salernitano (SAL) is an ancient Italian horse breed developed over the course of the ages together with Napoletano and, during the 20th century, by crossing with Thoroughbred horse lines. Excellent in hurdle jumping, this breed is currently facing a concrete risk of extinction due to the lack of appropriate management strategies. This research is the first SAL genetic characterization that aims to set up the basic knowledge for a conservation plan. A representative sample of 61 SALs was analyzed by means of a set of 16 microsatellites markers (short tandem repeats (STRs)). The sequence of hypervariable D-loop mtDNA region was also performed on a subset of 24 mares in order to study the maternal diversity and obtain a complete picture of the internal genetic variation. All the molecular data were analyzed together with those obtained from three Sicilian horse breeds investigated in a previous research (Siciliano, Sanfratellano and Sicilian Oriental Purebred). STRs markers revealed a moderate level of genetic diversity in SAL (alleles/locus 5.1, He 0.67) and confirmed the hunch of genetic erosion. Autosomal variability highlighted a very light deficit of homozygotes (FIS=-0.067). Experimental D-loop sequences were compared by multiple alignments with those retrieved from biological databases and revealed two unreported haplotypes. The phylogenetic network, which was built on mtDNA sequences, included various cosmopolitan and European horses and showed SAL haplotypes distributed among different mtDNA lineages.