A third said: “Sad for JP he wins the race but sadly the long mile is not coming home.”
A fourth wrote: “So sorry for The Long Mile and all connections at the stable.”
The Jockey Club has made several changes over the years to safety and welfare measures for riders and horses.
In the last decade, more than £2million has been spent on horse welfare measures on fences, landing areas and the ground at Aintree.
Both horses and jockeys are also required to meet stringent standards of fitness.
Every horse before the Grand National Festival also undergoes pre-race checks from a veterinarian to determine whether they are fit to race.
Races on the Grand National Course (three across the three-day Randox Grand National Festival) remain unique but fair challenges for horse and rider, but the evidence suggests, increasingly safer ones. Since 2012 there have only been two equine fatalities in the Randox Grand National from 318 runners.