It's not the most glamorous job - feeding, washing, walking and cleaning up after forgotten and unwanted pets.
Yet many invest hundreds of hours into caring for the vulnerable creatures at SPCAs around the country.
SPCA New Zealand chief executive Andrea Midgen said they have 5000 volunteers across the country - that's 10 volunteers for every paid staff member.
"We simply couldn't do the work that we do without the help of our amazing volunteers. They are the heart of the SPCA, and we rely so heavily on these in all areas of our organisation.
"We are very fortunate to have a range of volunteers from all areas of New Zealand and different stages of life."
The SPCA has volunteers who are retired, working or studying as well as young schoolchildren.
There are a range of ways they help the animals, including helping out at events, organising fundraising activities, working in SPCA op shops, assisting with administration, and being hands-on with the animals at SPCA centres.
Mary Olsen does just that at the SPCA Waipukurau Centre. She helps out twice a week as an animal care volunteer, but also as a foster parent.
She has been volunteering at the centre for about three years because of her great love of animals.
She has fostered about 10 puppies - and at one stage had eight in one sitting. "That lasted about three or four days. We split them up because they were a bit much for one volunteer."
She is a self-confessed cat-lover and has fostered kittens since she started giving her time to the SPCA.
"This week is National Volunteer Week and I would like to thank each and every volunteer who donates their time and energy to the SPCA," Midgen said.
"Their dedication helps all animals stay happy and healthy during their time at the SPCA – their contribution really does save lives."