Thieves stole nine dogs and 12 puppies from kennels on the outskirts of the town and three dogs are reported to be heavily pregnant, Northamptonshire Police say.
Offenders broke into the premises between 10pm on Tuesday, March 28 and 9.30am on Wednesday, 29 March, taking the dogs and puppies with them.
They broke padlocks to access the kennels and are believed to have cut through fencing to get to the location.
Northamptonshire Police have declined to say where the dogs were stolen from as it might identify the location of the other dogs.
The dogs taken include:
A female red Cocker Spaniel with six Cockerpoo puppies, aged six weeks
A female white/cream Cockerpoo, leaving behind a litter of puppies
Two pregnant female Schnauzers
A female black and tan King Charles Cavalier
A red and white King Charles Cavalier
A female Sable Cocker Spaniel with six chocolate and black Sable puppies
A female red Cocker Spaniel who is very heavily pregnant
A male black Toy Poodle
We are appealing for anyone who may have been offered any of the dogs or puppies for sale, or who may have any information about this incident to contact us.
Witnesses or anyone with information about this incident can contact police on 101 or Crimestoppers anonymously on 0800 111 555.