Letting a species go gracefully into the history books which is only there to service man isn't a huge loss. Most domesticated modern animals only reproduce out of a result of artificial insemination anyway.
To keep a species in existence to live a life of death & servitude isn't really something to aspire to in my view.
It's amazing the amount of effort people seem to go through to keep old breeds of domesticated animal from "extinction". On the other hand the problem with letting all breeds of a domesticated animal go the way of the dodo is that they are the closest link to the original wild animal. Many of the forebearers of our domesticated animals are now extinct. The last wild "cow" is believed to have been killed in Poland in the 1600s after it had been hunted from its range over most of Europe and beyond. The last wild horse may have been one that died in a zoo in Russia in 1909 (debateable - may have been much earlier).
Unfortunately these "useful" domesticated versions are all that we have left.