1.   But the zoo switched to hormone implants because keepers had difficulty keeping young chimps and males from eating the pills in the older, much smaller enclosure.

2.   Hormone implants and vasectomies have not been as successful as birth control pills, Stringfield said.

3.   The approaches being studied vary from different types of vaccines, to hormone implants, to morning-after pills.

4.   Without the corn, without the antibiotics, without the hormone implant, my brief career as a cattleman would end in failure.

5.   Menkhorst said the hormone implants will be tested for effectiveness as contraceptives for up to five years.

6.   Koala bears will be given vasectomies and hormone implants to ease overcrowding, the Victorian state government said Thursday.