Really surprised at the number of you advised AGAINST neutering by your vets, because of the risk of weight gain. All Guide Dogs for the Blind are neutered (many/ most of them labs!) and you will never see a fat one. If diet is controlled, there is absolutely no reason for a neutered dog to become overweight.
My dogs, cats and rabbits are/ will be done- mainly for health reasons. 70% of all RTAs are unneutered males- presumably out with one thing on their mind. lots of older dogs get testicular cancer, prostate problems and anal adenomas (which are hormone-related growths round their bum), and all these are preventable by neutering. In unneutered females, many have to have emergency hysterectomies due to a life-threatening condition where the womb fills with pus and can rupture, meaning major surgery in a very sick older bitch- not always a good outcome. Neutering at a young age also dramatically reduces the chances of mammary cancer in the bitch.
Cats are reflex ovulators, which means they get pregnant almost every time they get mated, and which can be harsh in young cats which are really just kittens themselves. Male cats left entire will spray, and also get into fights with other territorial males leading to wounds, abscesses and even blood poisoning.
And female rabbits are prone to a form of uterine cancer, so the general advice is to neuter them too!
Not trying to be arsey, but rather just to point out that there are medical reasons for neutering, which, to me, are far far more important than behavioural implications.