Barbaro with veterinarian Dean Richardson. © Jennifer Rench
Barbaro suffered a catastrophic leg fracture at the start of the Preakness Stakes in 2006 and died nearly nine months later due to laminitic complications.
Eight Belles was euthanized on the track after running second in the 2008 Kentucky Derby after suffering compound fractures of both front ankles.
Society president and chief executive Wayne Pacelle said the deaths sparked intense debate around training and breeding practices within thoroughbred racing.
His other stories included Hurricane Katrina in 2005, which devastated New Orleans. The suffering of animals in the wake of the disaster resulted in a federal law being passed requiring pets to be considered in disaster response plans. A raft of state laws were also passed requiring attention to animals in emergencies.
Pacelle also listed the dog-fighting scandal around NFL star Michael Vick in 2007, Oprah Winfrey's series on puppy mills, the resurgence of the Canadian seal hunt campaign, the release of the killer whale, Keiko, and the ongoing list of attacks on people by wild animals kept as pets or performers.