People never stop coming up with new ways to inflict suffering on animals, for their own convenience or amusement. A new trend in "sport horse" ownership is described in this article, wherein nursemare foals are deliberately produced and discarded to allow the mare to nurse a "more important" foal. However, people are out there rescuing them:

http://www.equestrianmag.com/news/orphaned-foals-saved-horses-rescue-7-07.html

This isn't the only way foals become a by-product of an unnecessary industry. PMU (pregnant mares' urine) products like Premarin invlove keeping horses pregnant so that their urine can be collected, for use in HRT (hormone replacement therapy). For more info on PMU and alternatives see http://www.nopmu.org

Wyeth is finally suffering the financial effects of producing drugs that cause cancer and other deadly diseases in women:

http://abcnews.go.com/Health/story?id=2770416

While the story seems to say that the horses will all be slaughtered solely because of the drop in popularity of Premarin and Prempro, the fact is that these horses face that fate regardless of the demand for the drug; the horses have a limited lifespan of "usefulness" for hormone production and are turned over quickly (as are their foals, at a rate of about one foal per PMU horse per year). The end of PMU drug production will see no new replacements for these horses, thus ending the cycle of cruelty. Ideally, the horses will be rescued and given good homes, user the new public scrutiny over the situation.

For more info, see http://www.nopmu.org