Massey University staff run the annual trips to the main island of Upolu as a special topic for students, and set up travelling surgical clinics to offer free neutering when a dog is registered.
This year, the first team of staff arrived in July, and the clinics will wrap up in September.
The July group neutered 200 dogs, Massey veterinary resident Malcolm Jack said, so 600 dogs could be operated on this year.
"If you do that every year, it makes a difference."