So, if we can get pet births down to replacement levels, problem solved?

Alfie looking for a home

Not entirely.

It's quite possible to have a situation where most of the young animals are wanted but there's still a substantial welfare issue about animals being discarded when they don't match owners' expectations.

It may be possible to solve this partially by a combination of education, help for otherwise good owners who run into financial difficulties and improvement of the conditions in which dogs are reared so that fewer end up with behaviour issues. However there will always be some people who die, get ill, lose their jobs etc. etc. and can't keep their animals for reasons that are not their fault. Barring an unlikely amount of improvement in human behaviour there will probably always be some owners who aren't suitable and a few who are actively cruel and whose animals must be removed.

So long as there are more people looking for animals than there are animals needing homes, this just means that animal shelters will still be needed, but most of their occupants will fairly readily be placed. Unfortunately it doesn't mean this will apply to all animals taken in.

Some animals will have chronic health conditions that make them less attractive to potential adopters (or simply unaffordable because of the cost of treatment). Some will be elderly. This doesn't mean it's going to be impossible to save them, just that the simplistic model of "find good home, problem solved" won't work. Realistically the majority of adopters want a pet with good prospects of being a companion they'll have for many years and few are going to consider a relationship they know will end in heartache in a few months or years.

This means high-quality, long-term fostering is likely to become more important to avoid elderly or difficult animals simply being warehoused in kennels.  Getting it right will be crucial, so that no-one is overwhelmed with the stress of looking after multiple animals who are approaching the end of their lives. Cost isn't the whole story; it's the cumulative load of animals needing to be taken to the vet nearly every week, tempted to eat and helped with grooming.

Cats and dogs

Virtually every week our branch gets requests for help with dogs or puppies who've been recently purchased and now have some kind of problem. Sometimes this is clearly the fault of the original seller; sometimes simply that the buyer had no idea how expensive vet treatment can be. It is really fantastically aggravating when we're asked to spend charity money treating a puppy we know would have cost quite a lot to buy.

It is extremely rare for us to get similar requests for help with cats or kittens, but we get lots of requests for help finding homes for unexpected/unwanted litters of kittens or for help catching and taming kittens which have been born to unowned mothers in people's gardens. Conversely, it's unusual for us to be asked to help with unwanted puppies, but we get a lot of requests for help with mother dogs who need expensive veterinary help giving birth and we sometimes have to take in litters of puppies who appear to have been dumped because they are ill (and therefore valueless).

There's a "pet population" problem for dogs and cats (and rabbits, ferrets, you name it), but the biology that underpins the problem isn't identical. To solve a problem you first need to understand it.

The non-pedigree cat population of mainland Britain is reproducing at a rate that makes it not only self-sustaining but over-producing. If no cats were ever imported and all pedigree breeding stopped, there would still be a "cat crisis" every summer, because most cats breed in spite of human activity, not because of it. We need to increase the percentage of pet owners who spay their female cats (currently around 80%; around 90% is needed to bring births and deaths in balance), and increase effort to trap and spay free-living cats who don't have owners.

(Bradshaw, J. W., Horsfield, G., Allen, J., & Robinson, I. (1999). Feral cats: their role in the population dynamics of Felis catus. Applied Animal Behaviour Science, 65(3), 273–283. doi:10.1016/S0168-1591(99)00086-6)

There is very little incentive for anyone to breed cats to make money because kittens are available from rescue centres at no more than the cost of neutering and vaccinating them.

The dog population is quite different; almost all breeding is the result of human selection and a very high proportion is aimed at making money. The "high-end" serious breeders, who care about their dogs, have to charge a lot because their costs will be high if they're doing expensive health checks on the parent dogs before deciding on a mating. Unfortunately this opens a marketing opportunity for breeders and traffickers who can produce a "product" (a living creature!) at lower cost, either by keeping their breeding bitches in dreadful "battery" conditions or by importing pups from countries where there is still over-production of unwanted litters (presumably because of lower rates of spaying and/or because it is more acceptable for dogs to be allowed to roam freely).

In these respects the "dog problem" is more similar to the "rabbit problem" than the "cat problem" because the driver producing more animals than can easily be rehomed is primarily commercial breeding and importing, not accidental litters. We could probably achieve 100% spay/neuter of the UK pet dog population and still have a problem of over-production of dogs because we have no way to "turn off the tap" in Ireland, Bulgaria or Romania.

A hundred years or so ago unwanted litters of pups were the major source of Britain's unwanted dogs. Affordable spay/neuter and a reduction in numbers of dogs allowed to roam unsupervised solved this, but made large-scale breeding for profit possible. As we approach the level of cat spay/neuter that should reduce cat breeding to replacement levels we need to learn from the earlier experience with dogs and avoid anything that might make commercial exploitation appear attractive. Cats and dogs are primarily companion animals and it's absolutely critical that they should be reared as far as possible in a domestic environment where they will have extensive social contact with people and other animals to avoid behaviour issues that will increase the risk of them becoming unwanted adults.

Useful links
BVA/AWF/RSPCA Puppy Contract
Advice about stray cats