I'm really not sure how keeping a "pet" cow in the backyard fits into the whole eating-locally ethos, but here's an offbeat story from the Times of London:
For between 200 and 2,000, people can buy a cow that stands no taller than a large German shepherd dog, gives 16 pints of milk a day that can be drunk unpasteurised, keeps the grass "mown" and will be a family pet for years before ending up in the freezer.
The Dexter, a mountain breed from Ireland, is perfect for cattle-keeping on a small scale, but other breeds are being artificially created to compete with it, including the Mini-Hereford and the Lowline Angus, which has been developed by the Australian government to stand no more than 39in high but produce 70% of the steak of a cow twice its size.
"People are realising that if you’ve got a couple of acres, you can just stick them there," said Sue Archer, the society’s breed secretary. "They eat grass so they are very cost-effective and they have a lovely temperament."
That bit about how they're "no taller than a large German shepherd dog" seems awfully suspicious: The Canadian Dexter Cattle Association says that full-grown cows stand 38 to 42 inches at the shoulder and weigh 750 pounds..