Traders visiting the Appleby Horse Fair 2010 are urged to obtain a Horse Passport.
Animal Health and Welfare Inspectors from Trading Standards will be raising awareness of the Horse Passport Regulations during the fair in June.
When a horse is sold the passport, which identifies the animal and proves ownership, is given to the new owner.
The fair is an annual gathering of Gypsies and travellers in Eden Valley. The 2010 fair runs from 3 to 9 June.
Organisers say horses at or on their way to Appleby, one of the largest events of its kind in Europe, must be accompanied by their passport.
New rules introduced from 1 July 2009 mean all foals born after that date, and any horses that have not previously been issued with a passport, must also be micro-chipped.
Organisers have warned any horse found straying at the fair, or taken into possession by the police, will be difficult to return to its owner if they do not have a passport as it is a definitive proof of ownership.
Organisers have also reminded owners that it is an offence to cause unnecessary suffering to any animal.
They say animals can only be transported if they are fit for their intended journey and the vehicle used is constructed in a way that will not cause injury or suffering.
Graham Winder, lead officer for animal health and welfare at Cumbria County Council's Trading Standards, said: "Horse owners have a duty to the animal to make sure it is registered and has a passport. People who don't do this are leaving themselves vulnerable to proving ownership.
"I would urge all people at the fair, whether they own a horse or are thinking of buying one that they don't buy or sell one without a passport."