The age can only be altered to Unknown. Please read below if you would like to understand the reasoning behind this policy
By law every horse should have a passport whilst still a foal so there should be no scope for error on its foaling year. In practice many owners are still applying for passports for older horses and we currently accept the year of foal provided by the vet on the application form.
We are sometimes contacted by owners whose vet or dentist has questioned the age on the passport. In these circumstances we accept the year of foal is in dispute and could be wrong and suggest it is changed to unknown. We will not change it to another specific year.
The reason for this policy is three fold:
1. Some dealers and owners will try and alter the year of foal in the passport to make a horse appear younger or more experienced than it actually is to increase its value.
2. In 1995 the Veterinary Record published a paper by JD Richardson, PJ Cripps and JG Lane from the Department of Clinical Veterinary Science, University of Bristol, Langford. They studied the accuracy of aging by dentition and used 434 Thoroughbreds with known dates of birth. The study concluded that ageing horses from their dentition did not offer an acceptable level of accuracy. For more information follow this link: http://veterinaryrecord.bmj.com/content/137/6/139.abstract
3. If the Horse Passport Agency states an alternative year of foaling in the passport it would give false assurances to anyone examining the passport when we know that the age of that animal is uncertain or in dispute. We consider it better to show the date as Unknown so anyone examining the passport (i.e Buyer) can make their own decision as to the age of the animal.
We recommend buyers of horses look at the passport issue date when considering the accuracy or “value” of any foaling date stated on a passport.