A mother and daughter from Holbury in Hampshire have been found guilty of four charges of causing unnecessary suffering to ponies.
Twenty-nine ponies belonging Debra (41) and Michelle (19) Green died after being left to live in appalling conditions, New Forest magistrates were told.
The pair from Holbury, a village near Southampton, denied the charges but were found guilty. They will be sentenced on March 20.
Jeremy Cave, prosecuting for the RSPCA, said 12 ponies were already dead when found in December 2006 and another 17 had to be shot.
They were lying or standing in mud and their own excrement and were suffering severe respiratory infections.