Executive director Peter Rizzo was commenting on findings from Florida agriculture officials that an overdose of selenium is the probable cause of death.
"The Florida Department of Agriculture report confirms that what happened to the Lechuza Polo Team was a tragic accident," Rizzo said.
He pointed to the association's decision to form a special committee "to examine additional safety measures and regulations to further protect our horses".
"We will examine these reports and develop a stronger prohibited substance policy that will ensure the safety and wellbeing of polo horses in the future," he said.
"The US Polo Association is 100 per cent committed to preventing a tragedy of this nature from happening in the future."