These are weaning bibs for mother dogs or cats that are trying to wean with your help.  These go on over the head and attach with velcro to make it more difficult for the puppies/kittens to nurse - helping Mom to wean them.  Bibs are available in polar fleece (for winter or short hair breeds) or knit ( for summer and long hair breeds).  Make sure you do allow weaning to progress slowly so Mom does not get engored or mastitis. Here are articles about nursing and weaning puppies which can also apply to most other mammals.