A Guinness representative was on-site to judge the event and present the World Record certificate in Louisiana.
Until now, the largest human mattress domino involved 550 people, a record achieved in 2011 in Kortemark, Belgium.
Mattresses for the event were donated, and will now go to various local charities.
Nicole Graham and her daughter were riding along Avalon beach in Geelong, southwest of Melbourne, when their horse Astro began to sink.
Ms Graham stayed with the 17-year-old animal while her young daughter Paris called for help.
After sedating the animal, rescue workers used a sling and a tractor to pull him very slowly from the mud.
Despite the three-and-a-half-hour ordeal, Astro escaped with only bruising, leaving one very relieved owner.