Veterinarians and police were called to the stables at the Carmona race track, in Cavite.
Lapus is one of the biggest owners in the racing industry in the Philippines, with about 25 racehorses.
Local media report that police are questioning one man over the attacks and are seeking another. Other reports suggest two are in custody and additional suspects are being sought.
The injured horses are unlikely to be back on the track within three months. Some may take as long as six months.
Some of the suspects have been described as "caretakers" who may have been angered over recently being "displaced".
It is believed the improvised knife used by the assailants was the one left embedded in the head of a horse called Serious Susie.
Picture can be viewed here (warning: graphic).