An RSPCA officer told Bicester Magistrates Court told how she found the rotting bodies of 20 animals strewn around an Amersham farm when she was called to the scene last January.
Kirsty Hampton was giving evidence on the second day of the trial of Buckinghamshire horse-dealer James Gray, his wife Julie, daughters, Jodie and Cordelia and a youth who cannot be named.
All five defendants deny 10 counts of causing unnecessary suffering to an animal, and two counts of neglecting an animal’s welfare.
Miss Hampton was called to Spindle Farm on 4 January. She told the court how she found two dead bodies of horses in a pen with nine live animals and drew Gray’s attention to the bodies of two more horses under a tarpaulin.
She said: “I asked him how the horses had died and he replied that you always get a few who die when you have this many.
“I asked him how they had died and he replied ‘the worms’.”
The RSPCA inspector also found horses in over-crowded pens with no clean water, feed or dry bedding.
One horse was so “painfully weak” it could not stand, while another had blood dripping down its leg from a serious infection.
More bodies, including those of two Shetland ponies, were dumped in other locations around the farm.
Miss Hampton alleged that Mr Gray had become aggressive towards the inspectors and threatened to set his dog on them and she later found one of the tyres on her van had been slashed.
The case continues.