But what are we missing out on by abstaining from other mammals' milk? Take the goat: Its milk is tangier, richer, and, to reasonable persons, much tastier than cow's milk. The superior flavor owes a great deal to the fact that goat's milk does not separate; the cream is knitted into the milk. Goats produce the most milk of any mammal relative to body size, which would make them attractive to industrial dairies if they weren't so small. At best, dairy goats are the size of a Newfoundland; milk output averages only around a few gallons a day. A direr failing: Goat's milk cannot easily be made into butter.
As for sheep's milk, almost no one in the United States or anywhere else drinks it straight. It has twice the fat of cow's milk and human milk, making it too rich to be very appealing as a beverage. This fattiness endears it to the world's artsier cheesemakers, who find in sheep's milk a profound communicator of terroir.
"The sheep people are a weird bunch," says one chef, who wanted to remain anonymous so as not to offend his favorite cheesemaker. "Sheep are difficult to raise, and fickle. You don't get much yield, and the cheese isn't that popular, so you're talking about an eccentric person. It's very difficult."
Unpalatable fat and protein levels keep some milks off the shelves, but the difficulty of milking recalcitrant beasts can be no less an obstacle. Consider water buffalo, which are raised in Campania, Italy, to make the otherworldly mozzarella di bufala but are otherwise little known in the West. Water buffalo are smart and watchful and have giant horns — in other words, they're dangerous — yet their milk has been a cornerstone of the most dairy-crazed cuisine in the world, that of India, for 1,000 years. Indian cooks use buffalo milk in cream sauces, boil and coagulate it for paneer, or reduce it to a paste called khoa that becomes the basis for desserts such as the rosewater-sweetened gulab jamun. The low availability of water-buffalo milk in the United States limits how authentic an Indian meal you can hope to have, and a few dairies are trying to fill the niche, but water buffalo are difficult animals for noobs to deal with.