How has modern science changed the care, breeding, and training of horses?

[Double S]

I have found the biggest difference is in breeding. It is much safer now that you can do artificial insemination and invetro fertilization. The stallion can get his jollies off on a phantom without the risk of being kicked and the mare has much less stress. Mares that are worth too much to risk foaling can be inseminated and the embryo can be flushed and put into another mare.

The underwater treadmill has also had a huge impact in the training of performance horses. There is less stress on the joints so horses can keep performing into their later years. Also lubricating injections for and advances in farrier's techniques (padded shoes, clips, bars etc) have extended the horse's working years.