"To neuter the dog" means to surgically remove the reproductive organs (testicles) of a male dog, which makes them unable to reproduce and can also help control some behavioral issues. Full definition
Four out of five studies show an increase in prostate cancer in neutered dogs; however, this cancer arises in only 0.2 % to 0.6 % of the population. (petsmagazine.ca)
There isn't a culture of neutering dogs here, so lots of people end up with puppies that they don't want and can't look after. (onegreenplanet.org)