The grain-sized implant releases a compound which results in suppression of the production of the hormones necessary for sperm production in males and estrus cycles in females.
Depending on the size of the implant, it is effective six or twelve months.
The benefits include managing feral populations, the procedure doesn't require surgery or anesthesia and leaves the options open if reproduction became desirable in the future.
Oddly, initially, after installation, the implant actually acts as a reproductive stimulant.
Kind of counter-productive, isn't it?
Still, though, an interesting idea and perhaps a stepping stone to something really cool in the future.
Source article:
Can Reversible Birth Control for Dogs Be a Reality?