More than 100 horses, ponies and donkeys were left to starve among the carcasses of other animals at a Buckinghamshire farm, a court heard.
The "horror scene" was uncovered after RSPCA inspectors were called to Spindle Farm at Hyde Heath in Amersham.
In total, 115 animals had to be rescued and removed from the farm in January.
James Gray, 45, Julie Gray, 41, Jodie Gray, 26, Cordelia Gray, 20, and a teenage boy are standing trial at Bicester Magistrates Court.
Bones and skulls
They face a total of 12 charges under the Animal Welfare Act 2006.
They relate to causing unnecessary suffering to, and failing to meet the welfare needs of, horses, ponies and donkeys.
The court heard body parts of horses that had been "left to die" were scattered around and a mound made up of bones and skulls was discovered.
There were 140 animals at the farm where a horse trading business was based, the court heard.
A judge was told vets described it as the worst case of animal cruelty they had ever seen.