The RSPCA is appealing for information after the puppy was discovered by a member of the public in Manor Road, Kempston Hardwick.
Its body was wrapped in a greyish cream blanket and a black bin bag with a supermarket shopping basket placed upside down to cover her.
The dog, which was not microchipped, was found on Monday (February 24) at around noon.
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RSPCA Inspector Stephen Reeves, who is now investigating, said: “This must have been a very distressing discovery for the member of the public who found this poor puppy and took her to the vets.
"An examination at the vets showed that the young Chihuahua had lots of abdominal bruising and a possible broken neck. We are very keen to find out what happened to this poor dog and how her body came to be dumped in this way.
“At this stage, the circumstances of the dog's death are unclear but her physical injuries do not appear to be consistent with a road traffic collision."
If you have any information about the dog and the circumstances leading to its death, call the inspectorate appeal line on 0300 123 8018.