-Whether your against slaughter or not (in America at least) it is banned, probably for good.. or a really long time. The overpopulated horses have nowhere to go, and now more than ever we need to think of them first and do our part.
-The horse market is in a slump right now. Basic economics and the law of supply and demand tell us if we reduce the numbers in the future, the market will slowly pick up.
-We are responsible as people to make the world a better place for future generations. As equestrians, we should do the same for our horses.
Where it starts:
-Leaving colts with their male parts, when they clearly aren't breeding material. Everyone likes to think their horse is the best, and they may have a lot of strengths... But if their strengths don't outweigh their weaknesses, they probably aren't breeding material. Not to mention, in the wild survival of the fittest takes over. There is ONE breeding stallion per herd (at least usually, sometimes some of the younger stallions probably sneak around). Stallions will fight to death for the control of a herd, the winner breeds all the mares.
-The same can be said for mares, if your mare is not truly breeding quality.. She shouldn't be bred. As much as you love her, its not going to change the fact that her babies might not be wanted by other people. If that is the case, and you don't have the time/money to take care of them: you are contributing needlessly to the overpopulation of horses. The wild also takes care of this in a way. First many mares may be infertile, in the wild they don't get pregnant. Thanks to technological advancement, we can increase a mare's chances of fertility. Secondly, foals who are born weak and cannot keep up with the herd usually die young. In the care of people, we do everything we can to ensure that they live.
I am not saying people should stop breeding. Nor am I saying that we shouldn't use technology to increase chances of impregnating mares, or that if our foal is born premature or weak we should let it die.
What I am saying is that because of human intervention, there is no longer a population control on horses (much like dogs and cats), so we MUST do our part to ensure that we can provide them the best oppurtunities to succeed, get loving homes, and if applicable be of competition status.
Where does it start?
Responsible breeding. Be honest with yourself. If your colt has poor conformation, a terrible/overly violent attitude, or isn't marketable within its breed (such as doesn't win at recognized shows) then maybe you should geld. It is my firm belief that only outstanding representations of their breed or great champions of their discipline (notice I am including crossbreds in here) should be kept stallions. The majority of colts should be gelded, there is nothing wrong with geldings, there should be nothing to fear in gelding a colt.
The same for your mare, broodmares should pass on the exceptional qualities of both sire and dam. They should also be exceptional representations of their breed or outstandingly talented in a given discipline... But even then, it doesn't garuntee that they will be "great" broodmares. If after two or three foals they don't seem to create outstanding or highly marketable foals, you should consider keeping them as companion/competition/pleasure horses.
The best way to do this, if you are an unproven breeder (If your foals sell out the shelves, keep doing what your doing.. its obviously something correct) is to ask the opinions of fellow horseman- especially those who know more about the breed or discipline of your choice than you, and those whose opinion you highly respect. They may bring out points, good or bad, that you haven't thought about. You may change your mind or your stallion.
The most important thing, is once the horse is bred and born no matter how beautiful, ugly, talented or average the horse is: It is your responsibility to ensure its marketability. That means training it. That means starting from a young age. (not necessarily saddling a two year old, but read on.) Get it used to clippers, bathing, leading, standing on cross-ties, stable manners, loading, standing for vet and farrier, grooms, etc. All of this can be done before the horse starts any real training and increase the horse's value.
Consider the future of the horse.. Just because you don't clip your horses, doesn't mean it shouldn't stand and be clipped for a future owner. Also squash bad behavior early (bucking, rearing, laying down in tack, etc.) before it becomes a full blown problem.. I think you know where I am going with this.
I think breeding responsibly is the best and only practical solution to slowing the exponential population growth. Just think of your horses' futures before you breed and after you breed.
Also proven breeders can do their part by considering reducing their foal crops.. Even if its just by one or two foals.. In a way this can be beneficial to you, again I bring in the law of supply and demand. If you lower your supplies, in theory the demand will go up. (So if your horses truly are of spectacular quality, having less will boost their prices.)
Stallion owners can also do their part. You can approve and limit the amount of outside mares you allow breedings to. If you are a good judge of quality (assuming so, since your stallion is of upmost quality if he is kept a stallion..) then don't allow breedings to mares who don't seem like they will produce outstanding babies. (Ask for pictures, pedigrees, foal references, etc.) If you don't want to get that technical, than just limit the number of outside mares. Again the law of supply and demand dictates that your stallion will be more valuable (provided he truly is a quality animal) as a breeding stallion, especially if he throws spectacular babies.
I think I've made my point. Any other suggestions for controlling population growth?