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microRNAs (miRNA) (Kim et al. 2014; Chhabra 2015; Van der Kolk et al. 2015). MicroRNAs are short sequences of single stranded RNA, 17–25 nucleotides long, which bind to mRNA transcripts to signal its destruction. In man, there are over 2000 miRNAs identified, many of which are conserved, which is helpful to equine researchers. They are quite elegant little entities and they hold promise as the basis for therapeutic agents. A delightful example of a miRNA right under our nose is that of the superb muscling of Texel sheep (I am sorry there is not yet an equine example). To look at its muscling one might think it shared the same myostatin mutation that double muscled cattle endure – not so. The mysotatin protein puts a check on muscle fibre development. In double muscled cattle, such as Belgian Blues, with the mutated mysostatin gene, the resulting myostatin protein is less active, leading to more muscle fibres being made during development (Kambadur et al. 1997). In Texel sheep, however, the defect is the result of the generation of an ‘illegitimate’ miRNA binding site. This novel site allows miRNA binding to the mysostatin mRNA, thus signalling the transcript for destruction and reduced translation into the protein product. Without mysostatin protein to keep the number of muscle fibres generated in check, the sheep develop massive musculature. While miRNAs are an extraordinarily hot topic in all areas


of medicine, especially cancer biology, a note of caution must be added. In this article, previously discussed nucleotide sequences have been very sequence specific – reliably so and reassuringly so. However, in the case of miRNAs, it is not obligatory that miRNAs have an entirely complimentary nucleotide sequence to their target sequence. When conducting research this fact makes it necessary to investigate the functionality of each new, inferred miRNA at the benchtop, rather than being able to rely totally on their prediction in silico – that is, on the computer! No discussion of genetics in an equine journal would be


complete without mention of the myostatin gene (MSTN)as it pertains to the performance horse. Observations in whippets had indicated that mutations in MSTN could bestow superior performance traits and increased muscling (Mosher et al. 2007). Reports published by Binns et al. (2010) and Tozaki et al. (2010, 2011, 2012) supported this observation in horses, and noted their predisposition to being suited to particular racing distances. Hill et al. (2010, 2012) went on to publish data on a T/C SNP in the MSTN gene locus, described as Chr18:g.66493737T>C (Bower et al. 2012; McGivney et al. 2012). After examination of detailed race records, it was found that a racehorse’s aptitude for particular racing distances could be correlated to whether it was homozygous TT or CC, or heterozygous TC at this location. Genetics tests, such as this one, are now available through commercial enterprises. Many of the genetic findings discussed here are simple,


single gene locus genetic traits. However, research continues to push forward the extent of our understanding as problems with complex genetic and epigenetic traits are investigated. With this in mind we should take heart in the knowledge that, while computers now do the heavy lifting, we humans are not ready to be called obsolete – far from it! The observation skills of astute horsemen/women and clinicians are critical contributions to this area of science, just like any area that has preceded it. This is not just in terms of sample collection, but the precise and meticulous descriptive phenotyping of our horse


patients becomes ever more important to tease out disease phenotypes and any possible genetic bases they may have. The field of genomics is having a meteoric impact on


furthering our understanding of equine health. It has implications in all aspects of veterinary care from treatment, management, disease diagnosis, to breeding decisions and so on. Veterinary science can also continue its sizeable contribution to human health as both fields benefit from crosstalk. Research and clinical communities must communicate better to integrate clinical cases and sample collection to pool the resources we have globally. Genomics is an exciting area to embrace, and your cases, your clients and your own mind will be the richer for embracing it.


Author’s declaration of interests No conflicts of interest have been declared.


Ethical animal research Ethical review not applicable for this review article.


Source of funding


No funding was received for this article. The author is supported by a Morris Animal Foundation stipend Fellowship.


Note aMitochondrial DNA (mtDNA) is not considered part of genomic DNA as mitochondria have their own, albeit much smaller, genome. Mitochondrial DNA is maternally inherited and often used in maternal lineage studies, in much the same way as the Y chromosome is used for paternal lineage tracing.


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