Two dozen rabbits were found dumped in a cardboard box in freezing conditions in Sheffield as snow fell across the city.
A member of the public found 25 rabbits abandoned in an alleyway near Landseer Drive, Gleadless Valley, on Saturday morning.
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Nine of the 20 newborn babies in the box have since died.
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RSPCA animal welfare officer Liz Braidley said: "Some of the rabbits had been fighting and a couple of the adults had sustained quite bad bite injuries as a result. Even one of the tiny babies had been bitten.
"One of the adults has severely infected eyes which appear to be from bite wounds sustained earlier, and is suffering a great deal as a result.
"We have lost so many of the babies it’s heartbreaking. They were so cold and underweight you could see their backbones."
AWO Braidley and colleague Kim Greaves, an RSPCA inspector, are caring for the rabbits at their own homes.
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AWO Braidley said: "They are in an horrendous state. They are having to be heavily medicated. Their injuries are having to be bathed. Some of them may have long term damage to their eyes.
"The weather was terrible on Saturday, it was freezing cold blizzard conditions. They would have all died if they hadn’t been found.
"The ones that have made it this far are doing okay. We’ll get them right. They won’t be going anywhere until we do."
Anyone with information on who owns the rabbits should call the RSPCA appeal line on 0300 123 8018 and ask to leave a message for AWO Braidley.