In the novel A Murder is Announced, Uncle Simon is mentioned by Mrs Swettenham as she is reading the Chipping Cleghorn Gazette and comes across an advertisement for dachshunds. She tells Edmund Swettenham that people seemed to be going crazy about breeding dachshunds. There are other breeds, for example Manchester Terriers which Edmund's Uncle Simon breeds.
Note that one of Christie's own dogs, Bingo, is a Manchester Terrier.