Effects of a 10-year conservation programme on the genetic diversity of the Pottoka pony--new clues regarding their origin

Here, we present the results of a genetic analysis of 463 Pottoka ponies corresponding to four generations, using 17 microsatellite markers. Ten years after the beginning of the Pottoka conservation programme, the values for the genetic diversity of the breed are still high and stable, indicating the success of the programme. We found null alleles in Pottoka for the ASB23, HMS3 and HTG10 microsatellites. Together with information obtained from other pony breeds from the Iberian Peninsula, this finding indicates that these microsatellites should not be used for phylogenetic analyses or parentage tests, at least for these breeds. The high heterozygosity exhibited by this breed in comparison to other ponies, together with its genetic proximity to the centroid of the allele frequencies, suggest that Pottoka allele frequencies are close to those initially exhibited by the ancestors of current European ponies. The results obtained in the current work, together with results from previous studies of ponies and horses from the Iberian Peninsula, corroborate the idea of a unique origin of all ponies from the European Atlantic Area. In contrast, our results do not corroborate the idea that these are derived from a domestication event in the Iberian Peninsula, nor that they have incorporated ancient Iberian horse genes into their genetic pool to a larger extent than other horse breeds.     

Molecular characterization and differentiation of five horse breeds raised in Algeria using polymorphic microsatellite markers

In this study, genetic analyses of diversity and differentiation were performed on five horse breeds raised in Algeria (Barb, Arab‐Barb, Arabian, Thoroughbred and French Trotter). All microsatellite markers were highly polymorphic in all the breeds. A total of 123 alleles from 14 microsatellite loci were detected in 201 horses. The average number of alleles per locus was the highest in the Arab‐Barb horses (7.86) and lowest in the thoroughbred breed (5.71), whereas the observed and expected heterozygosities per breed ranged from 0.71 (Thoroughbred) to 0.752 (Barb) and 0.71 (Thoroughbred) to 0.77 (Arab‐Barb), respectively. The genetic differentiation between the breeds was significant (p < 0.01) based on the infinitesimal model (F_ST). Three different approaches for evaluating the genetic relationships were applied. Genetic distances, the factorial correspondence analysis and structure analysis showed that a significant amount of genetic variation is maintained in the native horse populations and the other breeds. The Barb and Arab‐Barb breeds seem to be the most genetically related and support the decision to consider the breeds as same population.     

Genetic analysis of Mexican Criollo cattle populations

The objective of this study was to evaluate the genetic structure of Mexican Criollo cattle populations using microsatellite genetic markers. DNA samples were collected from 168 animals from four Mexican Criollo cattle populations, geographically isolated in remote areas of Sierra Madre Occidental (West Highlands). Also were included samples from two breeds with Iberian origin: the fighting bull (n = 24) and the milking central American Criollo (n = 24) and one Asiatic breed: Guzerat (n = 32). Genetic analysis consisted of the estimation of the genetic diversity in each population by the allele number and the average expected heterozygosity found in nine microsatellite loci. Furthermore, genetic relationships among the populations were defined by their genetic distances. Our data shows that Mexican cattle populations have a relatively high level of genetic diversity based either on the mean number of alleles (10.2-13.6) and on the expected heterozygosity (0.71-0.85). The degree of observed homozygosity within the Criollo populations was remarkable and probably caused by inbreeding (reduced effective population size) possibly due to reproductive structure within populations. Our data shows that considerable genetic differentiation has been occurred among the Criollo cattle populations in different regions of Mexico.     

Genetic characterisation of the Uruguayan Creole horse and analysis of relationships among horse breeds

The genetic variability within the Uruguayan Creole horse and its relationship to a group of geographically or historically related breeds (Spanish Pure-bred, Barb, Quarter horse, Paso Fino, Peruvian Paso, Arabian and Thoroughbred horse), was evaluated using 25 loci (seven of blood groups, nine of protein polymorphisms and nine microsatellites) analyzed on a total of 145 Uruguayan Creole horses. In this study, blood group and protein polymorphism variants that are considered to be breed markers of Spanish Pure-bred and Barb horses were detected in the Creole breed. Conversely, some microsatellites and protein polymorphisms alleles were found uniquely in the Creole horse. American horse breeds together with Barb and Arabian horses clearly formed a separate cluster from the Spanish pure-bred and Thoroughbred breeds, as shown by an UPGMA dendrogram based on Nei's standard genetic distance. Data in this study provided evidence for considerable genetic variation within Uruguayan Creole horses and of a distinctive breed profile. Both traits were most likely inherited from the XVIth century Spanish horses, more closely related to Barb than to Spanish Pure-bred.     

Genetic Characterization of Mangalarga Marchador Breed Horses Based on Microsatellite Molecular Markers

The Mangalarga Marchador (MM) horse breed has expressive importance in the Brazilian economy. Thus, the aim of this study was to investigate diversity in the MM breed. A database with a total of 3,193 genotyped horses was used (MM, n = 2,829; Andalusian – AND, n = 67; Pure Blood Lusitano – LUS, n = 43; English Thoroughbred – THO, n = 54; Arabian – ARA, n = 99; Campolina – CAM, n = 61; and Mangalarga – MAN, n = 40) for 13 microsatellite. Diversity parameters were estimates, such as mean number of alleles (Nm_a) and the number of rare alleles (AR), expected heterozygosity (He), F statistics, genetic distances, Hardy-Weinberg equilibrium test (HWE), population structure, and others. The Nm_a was 10.85, the AR was prevalent in the MM, and the He was 0.7402. In MM, the values of Fis (−0.0195), Fit (0.0566), Fst (0.0748), and deviations of HWE were observed. The genetic distances of the ARA and THO breeds with the other breeds were greater than the distances between the Brazilian breeds and between these and the breeds in the Iberian Peninsula. The population structure indicated that MM was substructured, yet there were some more genetically defined breeding farms. The genetic diversity is satisfactory for MM conservation, but the population is substructure, and parameters indicate moderate gene flow and the existence, though few, of crosses with other horse breeds. Immediate implementation of a genetic breeding program is required, especially seeking to conserve the structure of the MM breed as a well-defined genetic entity.     

Analysis of genetic diversity and the determination of relationships among western Mediterranean horse breeds using microsatellite markers

The distribution of genetic diversity and the genetic relationships among western Mediterranean horse breeds were investigated using microsatellite markers. The examined sample included seven Spanish and three Italian local horse breeds and populations, plus a Spanish Thoroughbred outgroup. The total number of animals examined was 682 (on average 62 animals per breed; range 20–122). The microsatellite marker set analysed provided 128 alleles (10.7 alleles per locus). Within‐breed genetic diversity was always high (>0.70), with breeds contributing about 8% of the total genetic variability. The mean molecular coancestry of the entire population examined was 0.205, Losino being the breed that contributed most. In addition to Nei's standard and Reynolds’ genetic distances, pair‐wise kinship distance and molecular coancestry were estimated. Remarkably similar breed rankings were obtained with all methods. Clustering analysis provided an accurate representation of the current genetic relationships among the breeds. Determining coancestry is useful for analysing genetic diversity distribution between and within breeds and provides a good framework for jointly analysing molecular markers and pedigree information. An integrated analysis was undertaken to obtain information on the population dynamics in western Mediterranean native horse populations, and to better determine conservation priorities.     

Mitochondrial Profiles of the East Bulgarian and the Pleven Horse Breeds

It is well known that horse breeding in Bulgaria is a cultural heritage in Bulgaria, dating from prehistoric and historic times. Until now, molecular data on Bulgarian horses from the plain regions of the country were not available. Therefore, for the first time, we have collected genetic information about some modern horse breeds from the plain regions in Bulgaria. A total of 50 horses originating from different families from two different breeds were investigated: the first one was the Pleven horse (n = 11, breeding in the Danubian Plain), and the second one was the East Bulgarian horse breed (n = 39, Shumen district). These breeds were genotyped according to the mitochondrial D-loop region. The results showed that the Pleven horse particularly carries the European haplogroup L (45.45%), followed by the Middle East haplogroup C (27.27%). In contrast to the Pleven horse, the East Bulgarian horse breed revealed almost equal frequencies of the European specific haplogroup L (33.33%) and the Central Asiatic haplogroup Q (35.90%). Analyses of these two horse breeds revealed a specific genetic profile, but it is obvious that the East Bulgarian horse showed an unusual, mixed profile—a massive admixture with the Asiatic-type haplogroup Q and a high haplogroup diversity. In conclusion, the differences in genetic structure of the two plain horse breeds may be explained with the various horse breeds involved in their formation.     

Molecular genetic studies of the "Einsiedler" horse population

In this study it was investigated whether the "Einsiedler" warmblood horse, a historically old horse population from central Switzerland (Abbey of Einsiedeln), is distinguishable from micellaneous horse breeds, using molecular genetic techniques. The breeding history of Einsiedler horses is characterised by systematic line breeding through the dams. Therefore, two Einsiedler dam lines (N = 28), going back to the middle of the 19th century according to pedigree entries, were the focus of the survey. Random samples of diverse warmblood horse populations, but also samples from more distinct types of horse breeds, served as comparison populations (N = 52).Variation in the mitochondrial genome appeared to be only partially informative to demarcate the studied horses, as horses of distinct breeds may share identical mtDNA sequence fragments. Both dam lines revealed haplotypes commonly found in Iberian horse breeds. This is to take as an indication on the genetic origin of Einsiedler horses. Furthermore, the Klima dam line held a homologous mtDNA sequence fragment with E. ferus przewalskii. Therefore, this seems to be a phylogenetically old haplotype. The analysis of microsatellite loci revealed that horses from the two Einsiedler dam lines were in fact distinguishable from more distinct types of horses, but not from closely related European warmblood horse breeds and English thoroughbred.     

利用微卫星分析康西草原马匹种群的遗传多样性和群体结构

旨在揭示康西草原马匹的品种来源以及群体遗传结构。本研究采集了当地60匹健康状况良好、体重适中、3～6岁之间不区分公母马的血液样品,试验分为6个种群并以纯血马等4个国外马品种、1个我国地方马品种作为对照， 通过设计引物并提取基因组DNA结合微卫星扩增法对染色体上12个微卫星位点的等位基因进行检测，并对各种群遗传多样性参数、群体分化指数、瓶颈效应以及群体结构进行分析。试验按照群体个数为依据分为6组，每组1个重复，每个重复以该组样本量为标准。分析6个种群马的遗传参数结果表明，其中共检测到221个等位基因,平均Shannon指数为1.691；有效等位基因数(Ne)为3.649～5.397；期望杂合度(He)为0.681～0.798；观测杂合度(Ho)为0.632～0.780；平均多态信息含量(PIC)为0.643～0.772。这些结果表明，6个群体都具有很高的遗传多样性。通过微卫星DNA位点的连锁不平衡及哈迪-温伯格平衡分析发现， 大多数位点的P值都大于校正值(P=0.006 5)，表示较多位点都处于哈迪-温伯格及连锁平衡状态。各群体间群体分化系数(Fst)表明，群体间分化程度较低(Fst<0.15)。基于Nei’s遗传距离与地理距离之间Mantel相关性检验显示二者之间呈现正相关性(R=0.502)，但未达到显著水平(P=0.310)；各马匹种群瓶颈效应分析表明，P值极显著(P_(IAM)<0.01)说明该地区的马群体受到过瓶颈效应的影响且该马群体历史上数量有大规模的减少。通过 FCA因子分析、基于Nei’s标准遗传距离UPGMA树状图以及Structure贝叶斯聚类分析发现，该地区马种群与纯血马和温血马聚为一类，说明该种群最有可能主要来源于温血马和纯血马。这些结果揭示，康西草原地区马匹具有较高的遗传多样性，该地马群体的血统与纯血马和温血马相近，这为当地马遗传资源评估以及开发利用打下了坚实的基础。     

Genetic analysis of three South African horse breeds

Genetic variability at 7 blood-group and 10 biochemical genetic loci was examined in 3 South African horse breeds, the Nooitgedacht, Boerperd and Basuto Pony. Observed heterozygosity for these breeds was intermediate for domestic horses, with the highest heterozygosity in the Boerperd and the lowest in the Basuto Pony. The 3 breeds show greater genetic similarity to each other than to other domestic horse breeds. Compared to other breeds, the South African breeds show greater genetic similarity to breeds such as the Thoroughbred, Holstein, Trakehner and Hanovarian and also to North American breeds such as the Saddlebred, Standardbred and Morgan Horse.     

Genetic Analysis of Three Lithuanian Native Horse Breeds

This study was the first to analyze the polymorphic characteristics of a wide range of genetic markers in three Lithuanian horse breeds. Genetic variation at seven red blood cell alloantigen (blood group) loci, 10 biochemical genetic loci and 16 microsatellites was examinated in 31 Zemaitukai, 30 large-type Zemaitukai and 24 Lithuanian Heavy Draught horse and compared to that of other domestic horse breeds. Genetic variability of the Zemaitukai breeds based upon blood groups and biochemical loci was higher than average for domestic horse breeds. For microsatellite loci, the variability of the large-type Zemaitukai and the Heavy Draught breeds also was high compared to the mean variation for domestic breeds; however, for the Zemaitukai breed, variation levels were very near the average for horses.     

Genetic diversity and differentiation of five Cuban cattle breeds using 30 microsatellite loci

Conservation and improvement strategies in farm animals should be based on a combination of genetic and phenotypic characteristics. Genotype data from 30 microsatellites were used to assess the genetic diversity and relationships among five Cuban cattle breeds (Siboney de Cuba, Criollo Cubano, Cebú Cubano, Mambí de Cuba and Taíno de Cuba). All microsatellite markers were highly polymorphic in all the breeds. The expected heterozygosity ranged from 0.67 ± 0.02 in the Taíno de Cuba breed to 0.75 ± 0.02 in the Mambí de Cuba breed, and the observed heterozygosity ranged from 0.66 ± 0.03 in the Cebú Cubano breed to 0.73 ± 0.02 in the Siboney de Cuba breed. The genetic differentiation between the breeds was significant (p < 0.01) based on the infinitesimal model (F_ST). The exact test for Hardy‐Weinberg equilibrium within breeds showed a significant deviation in each breed (p < 0.0003) for one or more loci. The genetic distance and structure analysis showed that a significant amount of genetic variation is maintained in the local cattle population and that all breeds studied could be considered genetically distinct. The Siboney de Cuba and Mambí de Cuba breeds seem to be the most genetically related among the studied five breeds.     

Morphofunctional diversity of equine of varied genetic compositions raised in the Pantanal biome of Brazil

Evaluating phenotypic diversity makes it possible to identify discrepancies in aptitudes among animals of different genetic bases, which is an indicator of adaptive or selective differences between populations. The objective of this work was to evaluate the morphofunctional diversity of 452 male and female adult equines (Arabian, Quarter Mile, Pantaneiro, and Criollo breeds, and undefined crossbreeds of horses and mules) raised in the Pantanal biome (Brazil). Linear measurements were performed to estimate conformation indexes. Initially, a discriminant analysis was performed, regardless of the animal’s size, followed by factor analysis. The factors were characterized and used as new variables. The diversity among equines and their relationship with the factors were evaluated using multivariate analysis. The factors were classified according to their decreasing importance: balance, rusticity, and robustness for the measurement factors; and load, ability, conformation, and equilibrium for the index factors. The genetic groups of equines have well-defined morphofunctional characteristics. The main differences are based on the rusticity and ability typologies in relation to those based on performance. Equines introduced to the Pantanal biome presented a more robust and compact body with good conformation. As a result, these horses may have superior athletic performance during equestrian activities when compared to the Pantaneiro local breed. However, this biotype may represent less rusticity (less adaptive capacity). Therefore, the regional breed can be equal or better in equestrian activities than breeds introduced to the Pantanal biome. Thus, breeders may cross horses from local breeds as an alternative to those introduced. Undefined crossbred male equines presented a different profile from the Pantaneiro breed, which may indicate little use of crossbreeds in breeding.     

Inheritance of racing performance of Thoroughbred horses

Horse racing is a contest between horses, usually held for the purpose of betting. Thoroughbred horse racing is the most diffused form of horse racing throughout the world. Thoroughbred is one of the most versatile of horse breeds and has influenced the development of many other breeds. Thoroughbred horses served as a foundation stock for the development of the light horse breeds. The two types of horse racing are flat racing and jumping races/steeplechases. The measures of racing performance are broadly classified into three categories. They are time and its several variations, handicap or similar performance ratings and earnings. One common measure of the performance of racehorses evaluated genetically is racing time or final time. The heritability estimates differed according to method of estimation, age, sex, track and distance. Time measure generally had a heritability in the range of 0.1 to 0.2 with the higher values for shorter races. For handicap and earning measures the heritabilities reported were generally higher in the range of 0.3 to 0.4; hence these may be considered in genetic evaluation of racing performance of Thoroughbred horses. The average generation interval of Thoroughbred horses was 11.2 ± 4.5 and 9.7 ± 3.8 years for males and females respectively, which limits the genetic progress in racing horses. However, the major advantage is that the racing performance may be evaluated in both males and females and repeated observations can be obtained on the same animal in relatively short periods. These factors coupled with the reasonable heritability of some measures of racing performance, suggest that mass selection based on performance tests would be the selection procedure of choice to improve the racing performance of Thoroughbred horses. In general, the inbreeding at the rate that is usually practised in Thoroughbred population does not enable much gene fixing. However, practice of close inbreeding may be avoided, even though it still fascinates breeders at subconscious level.     

建昌马mtDNA D-loop区遗传多样性及系统进化分析

试验旨在以线粒体DNA(mitochondrial DNA,mtDNA)为切入点,研究建昌马的母系遗传多样性与系统进化。从建昌马(n=39)血液中提取基因组DNA,用PCR方法扩增mtDNA D-loop区并直接测序,分析其高变区247 bp序列信息,统计mtDNA D-loop区的单倍型及变异位点,计算单倍型多样性(haplotype diversity,Hd)、核苷酸多样性(nucleotide diversity,Pi)和平均核苷酸变异数(average number of nucleotide differences,K)。构建包括建昌马在内的19个品种马的NJ系统进化树,计算各品种间的遗传距离。结果显示,试验获得了清晰的PCR扩增产物,并通过直接测序方法获得了约1200 bp的序列。39匹建昌马mtDNA D-loop区247 bp序列(其中1个样品缺失1 bp)的AT碱基含量为61.45%,属AT碱基对富集区,检测到33个多态性位点,共显示26种单倍型,其中4种为共享单倍型,且Hap7和Hap1为优势单倍型,单倍型多样性为0.947,核苷酸多样性为0.02399,平均核苷酸变异数为5.901,显示丰富的母系遗传多样性;NJ系统进化树显示,建昌马分布在A、C、D、E、F、G共6个支系中,约50%的样品分布在A支系,显示出复杂的母系起源;建昌马与关中马的遗传距离最小(0.021),其次是三河马、文山马、韩国车巨马(0.024),与韩国济州岛马遗传距离最大(0.032)。本研究结果表明,建昌马的mtDNA D-loop高变区遗传多样性丰富,具有多个母系起源,且A支系占有明显优势,与关中马、文山马可能有共同的母系起源。     

Inheritance of racing performance of trotter horses: An overview

Harness racing is a form of horseracing in which the horses race in a specified gait (trot or pace). In contrast to the Thoroughbred, the trotter is not an international breed. In this type, the horses are raced with trotting or pacing gait. Breeds specialized for racing at trot or pace are indigenous to many countries. Separate breeds of light harness horses, generally designated as trotters have evolved for racing purposes in several countries. The important horse breeds used for harness racing in different parts of the world are the Standardbred, French Trotter, Swedish Trotter, Orlov Trotter, Russian Trotter, Finnhorse, Icelandic Toelter, Dole horse and North-Swedish cold-blooded horses. The trotter ranks worldwide second to the Thoroughbred in popularity as a racehorse. Racing performance in trotters, in contrast to Thoroughbred is characterized by qualifying tests before entering the races, inclusion of more than one breed in international races only and greater duration of racing career. An intensive selection of stallions on the basis of phenotypic racing performance has been practised in many trotter populations for quite a long time. Unlike Thoroughbreds, improvements have been observed in different trotter populations and this is attributed to both genetic and environmental changes. Environmental changes include enhanced training methods, as well as improved tracks, harness and sulkies. As a result of selection, racing time of trotters has been reduced over the years. The estimated annual genetic progress in racing performance traits of Swedish Standardbred horses corresponds to 5% of the phenotypic standard deviation, 3.6% in French Trotters and 5% in Dutch Trotters. According to the recent selection for speed in trot, this trait remains heritable and genetic improvement is observed in most countries. Correlations between earnings and times are negative and high, and hence favourable. As a result, selection based on times and earnings are quite effective. A multiple trait approach avoids potential biases of one particular measure, even if the objective of all traits is much the same. Since racing performance may be evaluated in both males and females and repeated observations can be obtained on the same animal, mass selection based on performance tests would be the selection procedure of choice. In the future, interest in the possible use of marker-assisted selection (MAS) for enhanced genetic improvement in horses is likely to increase. MAS is likely to be a valuable complement to selection of horses based on estimated breeding values (EBVs) obtained by the Best Linear Unbiased Prediction (BLUP) method, rather than as a replacement for EBVs.     

Breed Differences in Dopamine Receptor D4 Gene (DRD4) in Horses

Genetic polymorphisms in genes related to neurotransmitters or hormones affect personality or behavioral traits in many animal species including humans. In domestic animals, the allele frequency of such genes has been reported to be different among breeds and it may account for breed differences in behavior. In this study, we investigated breed differences in horses in the dopamine receptor D4 gene (DRD4), which has been reported to affect horse personality. We collected samples from seven horse breeds including those native to Japan and Korea, and compared the sequence of the DRD4 exon3 region among these breeds. We found that there were two types of polymorphisms (VNTR and SNPs) in the exon3 region, and some of them seemed to be breed-specific. In addition, we found that the allele frequency of G292A, reported to be associated with horse personality, differed greatly between native Japanese horses and Thoroughbred horses. The frequency of the A allele which is associated with low curiosity and high vigilance, was much lower in native Japanese horses (Hokkaido, 0.03; Taishu, 0.08) than in Thoroughbreds (0.62). This difference may account for breed differences in personality or behavioral traits. Further studies of the function of these polymorphisms and their effect on behavior are indicated.     

Characteristics of equine summer eczema with emphasis on differences between Finnhorses and Icelandic horses in a 11-year study

Summer eczema, allergic dermatitis of the horse, was studied on 275 affected horses in Finland in 1997–2007. Features of the horses, clinical signs of the disease and owners'' opinions of aggravating factors were recorded. Differences, especially, between two of the native Scandinavian horse breeds, the Finnhorse and the Icelandic horse, were evaluated. The study was based on clinical examination and information from the owners. Of the horses, 50% were Finnhorses, 26% Icelandic horses and 24% consisted of different breeds of ponies and other horses. Of the Finnhorses, 76% had summer eczema by the age of 5 years, but in the Icelandic horses born in Finland the average age at onset was 7 years. The vast majority of the horses, 75%, had moderate clinical signs, while 16% showed severe and 9% mild. The severity of clinical signs did not depend on the duration of the disease nor was it related to the age at onset. The only linkage to severity was the breed of the horse or import from Iceland; New Forest ponies and imported Icelandic horses showed severe clinical signs significantly more often than Finnhorses. Of the owners, 38% regarded insects as the only aggravating factor, 24% mentioned several simultaneous factors, including grass fodder and sunlight, while 22% could not specify any. In Finland, a typical horse breed suffering from summer eczema is the Finnhorse and the characteristics of the disease are mainly uniform with the other breeds affected. Equine summer eczema seems to be aggravated by various combinations of environmental factors.     

Bite and kick injuries in horses: prevalence, risk factors and prevention

REASON FOR PERFORMING STUDY: Studies on the prevalence and predisposing factors of bite and kick injuries in horses have not been reported in a population-based data sample. OBJECTIVES: To investigate the prevalence of bite and kick injuries in horses and associated risk factors in a representative sample of horses in Switzerland. METHODS: A questionnaire on the incidence of disease and injury, which included the frequency of bite and kick injuries and their association with breed, housing, use and feeding regime, was sent to 2559 horse owners randomly selected throughout Switzerland. RESULTS: The data of 2912 horses with 897 disorders diagnosed by a veterinarian were analysed. There were 231 injuries, 50 (21.6%) caused by a bite or kick from another horse; this number corresponded to 5.6% of all diseases and injuries and concerned only 1.7% of all the horses evaluated. Warmblood, Thoroughbred and Arabian horses had a 4.3 times higher risk of bite or kick injuries than horses of other breeds. Eighteen per cent of injuries were associated with a change in housing management and occurred regardless of whether horses were kept in groups permanently or sporadically. CONCLUSIONS AND POTENTIAL RELEVANCE: A stable group hierarchy and a housing system that provides adequate space and is adapted to horse-specific behaviour are important factors in prevention and kick and bite injuries.     

Epidemiological features of 5009 cases of equine cryptorchism

Data from 16 North American veterinary university teaching facilities, 5009 cryptorchid horses, were analysed using relative risk methodology. In five breeds (Thoroughbred, Standardbred, Morgan, Tennessee Walking horse and Arabian), cryptorchism was diagnosed significantly (P less than 0.05) less frequently than expected by their representation in the hospital population. Three breeds, (Percheron, American Saddle horse and American Quarterhorse), plus ponies (as a group) and crossbred horses were significantly over-represented within the series. The over-representation of Quarter-horses was evident at each veterinary teaching facility. Other developmental defects and testicular tumours diagnosed in cryptorchid horses were presented. Analysis of the frequency of diagnosis of second anomalies among cryptorchids showed testicular hypoplasia to occur significantly more often, and inguinal and umbilical hernias less often, than expected (P less than 0.05).