The use of DNA technology is something most of us are familiar with – mostly thanks to its uses in human forensics. But its applications in the equine world, including DNA profiling for identification and parentage, screening tests for coat colour and some inherited diseases, are growing all the time. Of particular importance to all equine breed registries, regardless of size, is the production of DNA genotypes or profiles for individual horses, and the use of these profiles in verifying parentage of foals before registration.
This technology to produce a genotype for a horse is the same as that used in human forensics and parentage testing. The first step in any form of genetic testing involves isolating DNA from the individual involved. DNA is extracted from the hair follicle cells, and it contains the entire DNA sequence from all of the chromosomes of that horse. From this DNA, 17 species specific microsatellite markers are tested to generate the DNA profile for that individual. Each microsatellite marker has 2 alleles, one from each parent. The two alleles of the foal are compared with those from the dam and from the sire, for each of the 17 markers tested, to ensure that one of each pair has indeed come from the dam and one from the sire. This results in the production of the individual animals DNA profile, which can then be used for identification or for use in parentage verification. Parentage verification using this method is 99.9% accurate.
Equine parentage laboratories worldwide use the same base set of 12 markers, under the recommendation of the International Society of Animal Genetics, so that exchange of information can take place between laboratories and breed societies in different countries. This means that horses don’t have to be retested when they travel internationally, and when imported semen is used it can be accompanied by a DNA profile for use in parentage reporting for any offspring.
Sometimes the results produced are not as expected– there will always be surprises when dealing with horses! Some of the scenarios we see where there are mismatches between foal and/or dam and sire include mares swapping foals in the paddock, and stallions that should not have been with a particular mare using all sorts of devious means (sometimes seemingly impossible) to mate with said mare. Then there are the cases involving human error – mares can be misidentified, transcription errors can occur filling out the paperwork, and hair samples can be put in the wrong envelopes. But with DNA technology and some old-fashioned detective work we can now reach a conclusion on the vast majority of these difficult cases. It must be remembered that we can only produce parentage reports for a foal if we have the DNA profiles for the dam and sire on the database. For this reason, it is extremely important to test all breeding stock (or possible breeding stock) as soon as possible.
For horses, the sample of choice for DNA testing is hair – specifically the hair follicle cells attached to hair pulled from the mane or tail.
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