how many animals aren't lactose intolerant after infancy?

Lactose intolerance is the more common trait of adult animals. Some humans developed the ability to digest lactose as adults. They were populations that kept cattle or goats.

"A new Cornell University study finds that it is primarily people whose ancestors came from places where dairy herds could be raised safely and economically, such as in Europe, who have developed the ability to digest milk....

...Although all mammalian infants drink their mothers' milk, humans are the only mammals that drink milk as adults. But most people -- about 60 percent and primarily those of Asian and African descent -- stop producing lactase, the enzyme required to digest milk, as they mature. People of northern European descent, however, tend to retain the ability to produce the enzyme and drink milk throughout life."

http://www.news.cornell.edu/stories/2005/06/lactos...

Probably all animals are lactose intolerant as adults.

" After weaning, other mammals naturally graduate to life as a vegetarian, carnivore, or omnivore. Thus, there is no question of lactose intolerance in the animal world. Most adult animals refuse to drink milk. Although many people give domesticated adult cats milk in the mistaken belief that it is needed, cats that drink milk often have diarrhea due to lactose intolerance. In man, lactase activity drops at about age 2 or 3 and may be absent by age 5 to 10.[1"

http://www.medscape.com/viewarticle/482131