The eventing competition that begins Thursday at the Alltech FEI World Equestrian Games will feature a clash of champions.

Charging in from Germany, there's Michael Jung and his horse Sam, 2010 FEI World Cup eventing champions. The German program also is coming off gold-medal victories at the 2006 World Equestrian Games in Aachen, Germany, and at the 2008 Olympics in Beijing.

Eventing is often called the triathlon of equestrian events because it combines the disciplines of dressage, cross-country jumping and stadium jumping.

On the British eventing team are current Rolex Kentucky Three-Day Event champions William Fox-Pitt and Cool Mountain, 2009 European champions Tina Cook and Miners Frolic, and Pippa Funnell, the only rider ever to take the eventing Grand Slam by consecutively winning Rolex Kentucky, in addition to Badminton and Burghley trials, the two British four-star three-day events.

Representing Australia are 2010 Badminton winners Paul Tapner and Inonothing.

From New Zealand comes current Burghley champion Caroline Powell, and anchoring the Kiwi team is perhaps the most decorated rider today: Mark Todd, with three Olympic gold medals, three Badminton wins, five Burghley wins and two World Games titles.

In the American corner is two-time Olympic gold medalist Phillip Dutton and U.S. eventing champion Becky Holder.

One who won't be there after all: multiple Rolex Kentucky winner Kim Severson, who had to pull out Wednesday after her horse fell ill. Tipperary Liadhnan came down with cellulitis, an infection, a few days ago and "took a dramatic turn for the worse Tuesday morning," according to Mark Phillips, the U.S. team's chef d'equipe, or manager.

The last-minute withdrawal meant an alternate could not take her place, but individual competitor Karen O'Connor, riding Mandiba, will move up to give the United States a full team of four riders. All these award winners will go horseshoe to horseshoe, beginning with the dressage competition.

Eventing will feature 80 rider-and-horse pairs from 22 countries. It will take two days for each to ride through the dressage ring.

In dressage, each pair rides the same test pattern and is judged on how well they execute each move. The pair with the lowest score will be the leaders going into Saturday's cross-country ride, which is 4 miles of challenging obstacles.

The cross-country phase tests a horse's stamina and athleticism; a fall on the course results in elimination, even if both horse and rider are uninjured. Riders must complete the course inside an optimal time; going over that time limit will add points to their score.

Eventing competition wraps up Sunday with stadium jumping, with the riders competing in reverse order of standings. As in traditional show jumping, horses must clear a set pattern of jumps within a certain time. Each knocked-down rail adds four points to the score. The lowest score wins. Medals will be awarded for the top three individuals and national teams.

Reach Janet Patton at (859) 231-3264.