Identification of Differentially Expressed Genes after Endurance Runs in Karbadian Horses to Determine Candidates for Stress Indicators and Performance Capability

RNA sequencing makes it possible to uncover genetic mechanisms that underlie certain performance traits. In order to gain a deeper insight into the genetic background and biological processes involved in endurance performance in horses, the changes in the gene expression profiles induced by endurance runs over long (70 km) and short (15 km) distances in the blood of Kabardian horses (Equus caballus) were analyzed. For the long-distance runs, we identified 1484 up- and 691 downregulated genes, while after short-distance runs, only 13 up- and 8 downregulated genes (FC > |1.5|; p < 0.05) were found. These differentially expressed genes (DEGs) are involved in processes and pathways that are primarily related to stress response (interleukin production, activation of inflammatory system) but also to metabolism (carbohydrate catabolic process, lipid biosynthesis, NADP metabolic process). The most important genes involved in these processes therefore represent good candidates for the monitoring and evaluation of the performance of horses in order to avoid excessive demands when endurance performance is required, like ACOD1, CCL5, CD40LG, FOS, IL1R2, IL20RA, and IL22RA2, on the one hand, and, on the other hand, for assessing the suitability of a horse for endurance races, like GATA2, GYG1, HIF1A, MOGAT1, PFKFB3, PLIN5, SIK1, and STBD1.

Imputed genomes of historical horses provide insights into modern breeding

Historical genomes can provide important insights into recent genomic changes in horses, especially the development of modern breeds. In this study, we characterized 8.7 million genomic variants from a panel of 430 horses from 73 breeds, including newly sequenced genomes from 20 Clydesdales and 10 Shire horses. We used this modern genomic variation to impute the genomes of four historically important horses, consisting of publicly available genomes from 2 Przewalski's horses, 1 Thoroughbred, and a newly sequenced Clydesdale. Using these historical genomes, we identified modern horses with higher genetic similarity to those in the past and unveiled increased inbreeding in recent times. We genotyped variants associated with appearance and behavior to uncover previously unknown characteristics of these important historical horses. Overall, we provide insights into the history of Thoroughbred and Clydesdale breeds and highlight genomic changes in the endangered Przewalski's horse following a century of captive breeding.

Genome-wide survey on three local horse populations with a focus on runs of homozygosity pattern

Purosangue Orientale Siciliano, Sanfratellano and Siciliano represent the Sicilian equine genetic resource. This study aimed to investigate the genetic diversity, population structure and the pattern of autozygosity of Sicilian horse populations using genome‐wide single‐nucleotide polymorphism (SNP) data generated with the Illumina Equine SNP70 array. The genotyping data of 17 European and Middle East populations were also included in the study. The patterns of genetic differentiation, model‐based clustering and Neighbour‐Net showed the expected positioning of Sicilian populations within the wide analysed framework and the close connections between the Purosangue Orientale Siciliano and the Arab as well as between Sanfratellano, Siciliano and Maremmano. The highest expected heterozygosity (H_e) and contemporary effective population size (cNe) were reported in Siciliano (H_e = 0.323, cNe = 397), and the lowest were reported in Purosangue Orientale Siciliano (H_e = 0.277, cNe = 10). The analysis of the runs of homozygosity and the relative derived inbreeding revealed high internal homogeneity in Purosangue Orientale Siciliano and Arab horses, intermediate values in Maremmano and Sanfratellano and high heterogeneity in the Siciliano population. The genome‐wide SNP analysis showed the selective pressure on Purosangue Orientale Siciliano towards traits related to endurance performance. Our results underline the importance of planning adequate conservation and exploitation programmes to reduce the level of inbreeding and, therefore, the loss of genetic diversity.

A genome-wide scan for signatures of selection in Kurdish horse breed

The genetic diversity and genomic regions being under putative natural selection in Kurdish horse population were studied. The samples from 72 horses were genotyped by using GGP Equine 70K SNP arrays. The Ne Slope (NeS) analyses revealed that a sharp decline in Ne has probably occurred around four generations ago, and high frequency of ROH with 2-4 Mbp in length suggested that the inbreeding has probably occurred around 20 generations ago. The effective population size (Ne) was 104 horses up to three generations ago and the average inbreeding (F_ROH) was 0.047(±0.045). Using de-correlated composite of multiple selection signals (DCMS) and runs of homozygosity (ROH) analyses the genomic regions being under putative selection were detected. By using DCMS, a total of 148 significant SNP (FDR < 0.05) were identified, 40% of which were located on ECA9, where the greatest peak was observed. This genomic region harbors several known QTL which are associated with withers height (body size). Also significant genomic regions (FDR<0.05), harboring QTL associated with insect bite hypersensitivity (IBH), hair density and coat texture, alternate gaits, guttural pouch tympany and temperament were identified. By using outputs of ROH analyses, two hotspot regions (i.e. 30% of individuals was considered as threshold), were identified on ECA7 (50.11-54.36 Mbp) and ECA11 (26.10-29.07 Mbp) harboring QTL associated with withers height, alternate gait and IBH. In summary, the genomic regions being under putative natural selection which harbors known QTL associated with body size and IBH, among others, were introduced. Nevertheless, additional functional and comparative studies are necessary to corroborate their effect on the observed genetic and phenotypic diversity of the Kurdish horses.

Equine Genotyping Arrays

High-quality genomic tools have been integral in understanding genomic architecture and function in the modern-day horse. The equine genetics community has a long tradition of pooling resources to develop genomic tools. Since the equine genome was sequenced in 2006, several iterations of high throughput genotyping arrays have been developed and released, enabling rapid and cost-effective genotyping. This review highlights the design considerations of each iteration, focusing on data available during development and outlining considerations in selecting the genetic variants included on each array. Additionally, we outline recent applications of equine genotyping arrays as well as future prospects and applications.

Priming for welfare: gut microbiota is associated with equitation conditions and behavior in horse athletes

We simultaneously measured the fecal microbiota and multiple environmental and host-related variables in a cohort of 185 healthy horses reared in similar conditions during a period of eight months. The pattern of rare bacteria varied from host to host and was largely different between two time points. Among a suite of variables examined, equitation factors were highly associated with the gut microbiota variability, evoking a relationship between gut microbiota and high levels of physical and mental stressors. Behavioral indicators that pointed toward a compromised welfare state (e.g. stereotypies, hypervigilance and aggressiveness) were also associated with the gut microbiota, reinforcing the notion for the existence of the microbiota-gut-brain axis. These observations were consistent with the microbiability of behaviour traits (> 15%), illustrating the importance of gut microbial composition to animal behaviour. As more elite athletes suffer from stress, targeting the microbiota offers a new opportunity to investigate the bidirectional interactions within the brain gut microbiota axis.