The Ugly Dachshund (1966) on Netflix

Plot summary

Danke, the prize dachshund of Fran and Mark Garrison, is about to have a litter, and Fran dreams of a champion among the pups. Three female puppies arrive. At the clinic, the veterinarian, Dr. Pruitt, reports that a Great Dane mother has rejected one of her male puppies because she lacks milk, while Danke has more than she needs, so Mark brings the Great Dane home to nurse with the litter. Fran, surprised by the extra puppy, does not know it comes from another mother. Named Brutus, he grows up among the three dachshunds, copying the way they walk low to the ground and counting himself one of them. The dachshunds are mischievous, and Brutus joins their household mishaps while growing far too large to be a lapdog.