The charity has targeted 2m low-income households across the North East and North West, Wales and Northern Ireland.
Integrated agency 141 created 'OAP bus pass' leaflets that highlight the fact that neutered dogs tend to live longer.
The pass enables owners to pay just £25, compared with up to £120 at vets. It also features a competition with prizes donated by PetPlan.
The door-drop is the first in a series of four. Further activity is scheduled for September, November and January.
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