A pair of pit bulls (search) burrowed under a fence at a children's zoo and killed two goats and a rooster, officials said.

Nine other animals were injured at the Children's Zoo at Celebration Square (search) after the dogs got into the zoo sometime early Monday.

"It is a sad day at the zoo," Director Nancy J. Parker said.

One of the dogs was shot to death by a zoo employee while another was captured by animal control officers.

Saginaw County Animal Care Center Director Mark Wachner said he was not surprised by the pit bulls' attacks.

"That is just prey behavior," he said. "It is not that uncommon."