The worlds top riders have arrived at the MARS Badminton Horse Trials in Gloucestershire where the winner will take home 125,000, which is the most valuable first prize in eventing and represents the pinnacle of the sport.All eyes will be on the outstanding British partnership of Ros Canter, the world number four, and her superstar horse Lordships Graffalo. The defending Badminton champions are bidding for a record third win together and will perform their dressage test at 10.48am on Friday morning.Thirteen of the top 20 in the newly adjusted FEI World Eventing Rankings are competing at Badminton, including the top three. World number one Harry Meade opens proceedings tomorrow at 10am with Et Hop Du Matz, the first of his three rides.New Zealander Tim Price (number two), performs his dressage test at 2.40pm on Friday with Falco, and reigning European champion and Olympic gold medallist Laura Collett (number three), riding the mare Bling, will be in the arena also on Friday, at 12.12pm.The first session of dressage tomorrow morning will feature leading British riders Gemma Stevens and David Doel, plus New Zealander Caroline Powell, a Badminton winner in 2024, and Irelands Austin O Connor.The LeMieux Grassroots Championships took place today and saw a convincing victory in the BE100 for Philippa Hendry riding her own Flyer Des Coupeaux, a prolific winner at this level. Philippa, who with her husband runs a vineyard in Marlow, Buckinghamshire, could enjoy the luxury of a record-breaking dressage score in this competition of 19.8, to which she only added five show jumping penalties.Holly Jessett, a primary-school teacher from Northamptonshire, captured the BE90 with her own Irish-bred Lombard Lad, a horse she has produced from the start seven years ago, adding nothing to her dressage score of 27.1.The Dubarry Burghley Young Event Horse qualifiers for future stars took place today with victories for Hayden Hankey and Chris Makins MSHI Rockstar Le Tot in the four-year-old category and Olympic gold medallist Tom McEwen riding Vicky Bates, Magda Gut and Annabelle Timmiss Caunton Pollyanna in the five-year-old section.All the action can be followed on Badminton TV and Badminton Radio.