William delved into the thoroughbred breeding behind many of the successful horses.
He says that, in most cases, the same TB blood appeared in all three disciplines, but in particular in both showjumping and eventing.
"This is understandable because of the specific need to jump in both disciplines, but I also believe it is because of the inheritance of specific mental qualities," he says.
"In the case of eventing sires, it is apparent that the exceptional trots of those such as Master Imp, Heraldik and Stan the Man are also an essential part of the recipe, together with all the other required attributes."
William's research confirmed to him how dependent success is on the opportunity that sires have well-produced offspring.
"One of the main reasons top Irish sires tend to be recognised so late in life, and be sent their best mares late in their career, is because so many of their offspring are badly produced initially," he says.
The Cavalier effect
Cavalier Royale was by the Selle Francais Cor de la Bryere out of the Holsteiner Ligustra. Cor de la Byrere is two-thirds thoroughbred and Ligustra slightly more than one-third, making Cavalier Royale himself just over half thoroughbred.
Most of Cavalier's famous offspring are out of thoroughbred Irish mares, so they are three-quarters thoroughbred.
"The success of Cavalier Royale with TB mares as an event sire was no accident as he is just over 50pc TB and carries the premium TB genes of four of the five great TB gods of the warm blood world -- Furioso, Rantzau, Ladykiller and Cottage Son," he says. "The fifth TB warm blood god is Lucky Boy.
"There is no statistical doubt that these five thoroughbred stallions are the equal of Northern Dancer and his son, Sadlers Wells, in the racing world. They are more influential than any other sires of any breeding in the jumping world -- and they are thoroughbreds," he says.
"These TB sires, all of which are Irish or have strong Irish connections, and their approved sire sons (more than 140) are so dominant on the continent that today it is difficult to find any jumping horses at a higher level without their genes," he says.
"The success of Ben Faerie, Master Spiritus, Master Imp and Heraldik is also not an accident. They have good genes as well as all their other qualities.
"Of course, the right genes are only one element and it is true that many with these genes are not successful but, for the breeder, the key finding is that it does seem that few horses make the grade without these genes."
Few top event horses have sprinting genes but, unsurprisingly, they do have typical flat racehorse National Hunt blood and, in particular, long distance flat blood, as long as this is also jumping blood -- and they have good trots, insists William.
New TB sires
"In the 20 years after the Second World War, the German and Dutch breed societies made a decision to import thoroughbreds to cross with their native mares to produce show-jumpers," recalls William.
"The big question today is whether the decline in new TB sires is the result of more quality, part-bred sires being available or the result of the success of the marketing policies of the breed societies, or a little of both.
"The success of TB sires born in the 1980s would suggest that there are new openings and open minds for the thoroughbred in all disciplines. Although specific sires for sport horses are the way to go, the TB genes have to be improved at intervals by the best of racehorse genes."
Irish Draught effect
William insists that the inclusion of Â¼ Irish Draught is a major factor in the success of the Irish event horse, and he maintains that the continuing availability of Irish Draught bloodlines that jump will be a vital factor in future success.
"Their 'fifth leg' intelligence and amenability -- all largely genetic factors -- provide a winning edge and a significant aid to safety in international event horses," he insists.
Taking a look at specific bloodlines, William lists 10 TB ancestors that any breeder should be delighted to find in their horse's pedigree.
They are Galopin, St Simon, Bay Ronald, Rondeau, Chaucer, Dark Ronald, Bayardo, Fair Play, The Tetrarch and Son in Law.
These "oldies but goodies" are the common ancestors of the five TB gods of the warmblood world -- Furioso, Rantzau, Ladykiller, Cottage Son and Lucky Boy -- and the other 165 TB eventing sires he examined.
The table (left) shows 11 slightly more modern thoroughbreds.
However, he adds that there are another 18 sires that are of particular value statistically, based on the performance of their families and their exceptional jumping ability.
"They are bloodlines that produce good brains, paces and jumping ability," William says. "Not all horses with these genes are great horses but the fact is that there are few superstars without these genes in abundance."
The 18 'golden ones':
•Blandford (and his offspring Umidwar and Wild Risk);
•Fairway (and his brother Pharos and his son Fair Trial);
•Tourbillon (and his son Djebel and grandson Hugh Lupus);
•Hyperion (and his offspring Owen Tudor and High Hat);
•Precipitation (and his offspring Furioso and Prefairy);
•Chanteur (and his offspring Ben Hawke and Chateau Bouscaut).
In looking for the next generation of top sires, William says we should first recognise that TB horses bred along these lines have been huge successes in the sport horse breeding world throughout Europe in recent times. He highlights sires such as Ecuador, High Top, Prince Thatch, Lauries Crusador and Black Sky in dressage and Julio Mariner, Sacramento Song, Mytens and Hand In Glove in showjumping.
In eventing, he picks out the sires of Faerie, Master Spiritus, High Top, Primitive Rising, Blakeney, Mayhill, Shaaab, Edmund Burke, Bassompierre, Fines, Stan The Man and Broadsword.
"It would appear that these TB horses may well make a similar contribution in eventing: Beauchamp King, Clerkenwell, A Fine Romance (Canada), Double Trigger (UK), Ghareeb, Power Blade and Golden Master," he says.
He also highlights three horses close to TB, Jaguar Mail (87.5pc TB, France), Mighty Magic (87.5pc TB, Germany), and Jackaroo (96.8pc, TB). Jackaroo is William's own stallion, a son of Master Imp and full brother to the geldings Mandiba, ridden by Karen O'Connor, and High Kingdom, ridden by Zara Phillips, and his mare Nuff Kisses.
He adds the names of some part-bred sires that he considers to be in the same elite category and suitable for TB mares. These include Puissance (62.5pc TB), Kings Master (62.5pc TB), Condios (55pc TB), Ricardo Z (50pc TB), and Jumbo (41.5pc TB, GB).