Got milk? Well, in the case of Toma, the Amur tiger at the Pittsburgh Zoo & PPG Aquarium who gave birth to a single cub on Sunday, maybe not enough.

Toma, who nursed her newborn briefly but has since shown little interest in that and other mothering duties, was examined by zoo veterinarians yesterday and found to have little to offer the hungry boy.

"She didn't seem to have a lot of milk," said Dr. Barbara Baker, after the morning examination in which Toma was immobilized, X-rayed and given a battery of tests that found nothing else unusual. "We've injected her with a drug to stimulate milk production and we should see a response in one or two days."

In the meantime, the zoo veterinary and keeper staff will continue to bottle feed the as-yet-unnamed cub every four hours with a cat milk replacement product commonly used to help raise domestic kittens. If Toma doesn't resume nursing, the bottle feeding could continue for six to 10 weeks.

The new cub, which weighed 1 kilogram -- 2.2 pounds -- at birth, is maintaining its weight, Dr. Baker said, which is a good thing. The cub seems to be feeding, excreting and breathing normally, and Toma and her new son continue to share a den at the zoo.

"She's not letting the cub nurse, but he is active and moving round, trying to find his mom," said Dr. Baker, who explained that like all newborn tigers the cub will not be able to open its eyes for 10 to 14 days.

Dr. Baker said Toma's nursing problem is surprising because she successfully nursed her first litter of three cubs born in August 2006.

"She's nursed before and that makes this particularly unusual," she said. "We're perplexed as to why she is not attentive. She was good with the first ones."

Dr. Baker theorized that Toma may sense that the cub has an unseen, and at this time undetectable, birth defect. She said it's not uncommon for female domestic cats to take care of and favor some kittens in a litter and ignore others that are smaller or that she senses may have a problem.

One of the three cubs Toma gave birth to in 2006 -- the runt of the litter -- died when it was 5 weeks old. It was subsequently discovered to have had a heart defect and hydrocephalus, commonly termed "water on the brain." But Toma did not reject that female cub.

Amur tiger cubs have a 30 percent to 40 percent mortality rate, whether born in the wild or in captivity.

Formerly called Siberian tigers, Amur tigers are endangered worldwide. There are less than 400 known Amur tigers in the wild, and 190 more live in zoos in the United States. Other sub-species of tigers -- Bengal and Sumatran tigers-- are also endangered. The Sumatran tiger is the rarest of the three.

Because of their endangered status, tiger breeding in zoos is planned and monitored by the Association of Zoos and Aquariums. The Pittsburgh zoo's Toma mated in late January with Globus, a 12-year-old Russian-born male brought in from the Bronx Zoo for that purpose late last year.

Coincidentally, Globus was rejected at birth by his mother. He was bottle fed by the owner of the Russian reserve after his mother abandoned him and his brother. The brother did not survive.