Gordon Elliott has admitted the image is real and has apologised.
Organisers were eventually told that, from Thursday, the event must be held behind closed doors – but thousands are already there.
Premier League football is set to return on June 17, with horse racing due to resume as early as Monday at Newcastle.
"I wrote this same exact tweet after you got elected."
Activists have called for better safety precautions.
Crucial Role was injured in a "horrific fall".
“The industry chooses to race-on after horses are killed on racecourses”.
All races have been called off on Thursday.
'Gives him a pat and gets the saddle off as well'.
Animal activists say event in sweltering heat was a 'disaster waiting to happen'.