The three horses have been given two-month suspensions from the FEI as a result of the cases, the first involving the drug, which increases blood flow and is used to treat peripheral and cerebral vascular disorders.

R S Nube Blanca, ridden by Gaje Singh Hari Singh of India, tested positive for the substance in a 120-kilometre event at Mesaieed in Qatar on November 19.

Acqua Vela and rider Maryam Ahmad S A Al Boinin of Qatar won the 90-kilometre competition on the same day and also returned a positive test for diisopropylamine.

Both were tested on the day of the race.

Samples provided by Tarifa, the third horse involved which was ridden by Oman's Mattar Said Khalfan Al Saadi, at an 80-kilometre event in the same Qatari city on January 7, also contained the drug.

As trainer of both the Qatari horses, R S Nube Blanca and Acqua Vela, Waleed Said Khalfan Al Saa'di has also been handed a provisional suspension.

Under FEI rules, banned substances such as diisopropylamine "should never be found in the body of a horse".

Earlier this month, the FEI announced a series of measures aimed at addressing concerns over horse welfare in the United Arab Emirates (UAE) after revealing that seven horses have tested positive for banned substances there.

The seven doping cases have come as a result of competitions at the Al Wathba venue in Abu Dhabi, with the positive tests occurring after four different endurance events.

Each of the horses tested positive for four prohibited substances: the stimulant caffeine and its metabolites theophylline, theobromine and paraxanthine.