Half a century of equine reproduction research and application: A veterinary<i>tour de force</i>

Allen, W. R.; Wilsher, S.

doi:10.1111/evj.12762

Cited by 25 publications

(17 citation statements)

References 77 publications

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“…These horses may not appear in the pedigree of future Thoroughbreds, such that the values from their generation will show minimal variation. The decreasing average genetic value conflicts with an increased foaling rate reported in recent years [36]. It is likely that the improving fertility rates in the population are due to better management techniques rather than genetic gain.…”

Section: Discussionmentioning

confidence: 99%

“…It is likely that the improving fertility rates in the population are due to better management techniques rather than genetic gain. Recent advances in veterinary treatments has led to widespread use of hormonal therapies to increase foaling rate [36]. Increasing commercial demand for mares with good fertility may explain the outlying individuals with high genetic potential in recent years.…”

Section: Discussionmentioning

confidence: 99%

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The effects of inbreeding on covering success, gestation length and foal sex ratio in Australian thoroughbred horses

et al. 2020

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Background: Horses produce only one foal from an eleven-month gestation period, making the maintenance of high reproductive rates essential. Genetic bottlenecks and inbreeding can increase the frequency of deleterious variants, resulting in reduced reproductive levels in a population. In this study we examined the influence of inbreeding levels on foaling rate, gestation length and secondary sex ratio in Australian Thoroughbred mares. We also investigated the genetic change in these traits throughout the history of the breed. Phenotypic data were obtained from 27,262 breeding records of Thoroughbred mares provided by three Australian stud farms. Inbreeding was estimated using the pedigree of each individual dating back to the foundation of the breed in the eighteenth century. Results: While both gestation length and foaling rate were heritable, no measurable effect of inbreeding on either trait was found. However, we did find that the genetic value for both traits had decreased within recent generations. A number of environmental factors also had significant effects on foaling rate and gestation length. Secondary sex ratio had only an extremely small paternal heritable effect and was not susceptible to environmental influences. Conclusions: In contrast to racing performance, inbreeding had no measurable effect on foaling rate or gestation length in Australian Thoroughbred horses. This could be because the level of inbreeding in the population examined is not high enough to show a discernible effect on reproductive traits. Populations that experience higher levels of inbreeding due to use of artificial reproductive technologies or extremely small population sizes may show a more pronounced reduction in natural foaling rate or gestation length. It is also possible that the intensive management techniques used in the Thoroughbred population masks any negative effects of inbreeding. The decrease in the genetic value of foaling rate is likely to be because horses with unfavourable genetic potential have not yet been selected out of the population. The change in genetic value of gestation length may be due to selective breeding favouring horses with shorter pregnancies. We also found that prioritising the mating of older mares, and avoiding out of season mating could lead to an increased breeding success.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The effects of inbreeding on covering success, gestation length and foal sex ratio in Australian thoroughbred horses

et al. 2020

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“…Maintaining good fertility rates is particularly important for horse populations due to the seasonal nature of breeding and the low individual fertility output, as mares produce only one foal from an eleven month gestation period 32 . Despite the extensive use of hormonal therapies to increase covering success in many domestic horse populations, per cycle pregnancy rates in some breeds only average around 65%, suggesting the presence of unknown variables that may reduce fertility 33 .…”

Section: Introductionmentioning

confidence: 99%

A genome-wide scan for candidate lethal variants in Thoroughbred horses

Todd

Thomson

Hamilton

et al. 2020

Sci Rep

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Domestic animal populations are often characterised by high rates of inbreeding and low effective population sizes due to selective breeding practices. These practices can result in otherwise rare recessive deleterious alleles drifting to high frequencies, resulting in reduced fertility rates. This study aimed to identify potential recessive lethal haplotypes in the Thoroughbred horse breed, a closed population that has been selectively bred for racing performance. In this study, we identified a haplotype in the LY49B gene that shows strong evidence of being homozygous lethal, despite having high frequencies of heterozygotes in Thoroughbreds and other domestic horse breeds. Variant analysis of whole-genome sequence data identified two SNPs in the 3′UTR of the LY49B gene that may result in loss of function. Analysis of transcriptomic data from equine embryonic tissue revealed that LY49B is expressed in the trophoblast during placentation stage of development. These findings suggest that LY49B may have an essential, but as yet unknown function in the implantation stage of equine development. Further investigation of this region may allow for the development of a genetic test to improve fertility rates in horse populations. Identification of other lethal variants could assist in improving natural levels of fertility in horse populations.

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“…Maintaining good fertility rates is particularly important for horse populations due to the seasonal nature of breeding and the low individual fertility output, as mares produce only one foal from an eleven month gestation period (33). Despite the extensive use of hormonal therapies to increase covering success in many domestic horse populations, per cycle pregnancy rates in some breeds only average around 65%, suggesting the presence of unknown variables that may reduce fertility (34).…”

Section: Introductionmentioning

confidence: 99%

A genome-wide scan for candidate lethal variants in Thoroughbred horses

Todd

Thomson

Hamilton

et al. 2020

Preprint

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2Recessive lethal variants often segregate at low frequencies in animal populations, such that two 3 randomly selected individuals are unlikely to carry the same mutation. However, the likelihood 4 of an individual inheriting two copies of a recessive lethal mutation is dramatically increased by 5 inbreeding events. Such occurrences are particularly common in domestic animal populations, 6 which are often characterised by high rates of inbreeding and low effective population sizes. To 7 date there have been no published investigations into the presence of specific variants at high 8 frequencies in domestic horse populations. This study aimed to identify potential recessive lethal 9 haplotypes in the Thoroughbred horse breed, a closed population that has been selectively bred 10 for racing performance. 11In this study, we scanned genotype data from Thoroughbred horses (n = 526) for adjacent single 12 nucleotide polymorphisms (SNPs) at high heterozygote frequencies, but with a complete absence 13 of homozygotes. Two SNPs that matched these criteria were mapped to an intronic region in the 14 LY49B gene, indicating that a closely linked mutation may cause lethality in homozygous state. 15 Despite a complete absence of homozygotes, almost 35% of Thoroughbreds included in these 16 analyses were heterozygous for both SNPs. A similar loss or absence of homozygotes was 17 observed in genotype data from other domestic horse breeds (n = 2030). Variant analysis of 18 whole-genome sequence data (n = 90) identified two SNPs in the 3UTR region of the LY49B 19 gene that may result in loss of function. Analysis of transcriptomic data from equine embryonic 20 tissue revealed that LY49B is expressed in the trophoblast during placentation stage of 21 development. 23 variant causing lethality in homozygous state. These findings suggest that LY49B may have an 24 essential, but as yet unknown function in the implantation stage of equine development. Further 25 investigation of this region may allow for the development of a genetic test to improve fertility 26 rates in horse populations. Identification of other lethal variants could assist in improving natural 27 levels of fertility in horse populations. 28 Author Summary 29Recessive lethal mutations may reach high frequencies in livestock populations due to selective 30 breeding practices, resulting in reduced fertility rates. In this study, we characterise recessive 31 lethal mutations at high frequencies in the Thoroughbred horse population, a breed with high 32 rates of inbreeding and low genetic diversity. We identified a haplotype in the LY49B gene that 33 shows strong evidence of being homozygous lethal, despite having high frequencies of 34 heterozygotes in Thoroughbreds and other domestic horse breeds. Two 3'UTR variants were 35 identified as most likely to cause loss of function in the LY49B gene, resulting in lethality. This 36 finding provides novel insights into the potential importance of LY49B in equine development. 37Additionally, this study may assist with...

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Half a century of equine reproduction research and application: A veterinarytour de force

Cited by 25 publications

References 77 publications

The effects of inbreeding on covering success, gestation length and foal sex ratio in Australian thoroughbred horses

The effects of inbreeding on covering success, gestation length and foal sex ratio in Australian thoroughbred horses

A genome-wide scan for candidate lethal variants in Thoroughbred horses

A genome-wide scan for candidate lethal variants in Thoroughbred horses

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