I’m sure that, with some effort, they could have found some other way to do that.
This is one of those situations where I can see both with the eyes of an animal welfarist and with those of a ranch hand. The animal welfarist says, “Why are you doing that with no anesthetic?!? With your teeth? Why are you castrating them at all? You could just [insert high-maintenance management program, expensive castration alternative, or impossible immediate job switch here]!” The ranch hand says, “I have 1,600 sheep to do — can you imagine what it would cost, or how long it would take to anesthetize every one? Or to separate every adult ram, because they’ll fight?”
(Hate this problem? Ask why they have 1,600 baby sheep — they have such a large flock because they’ve been forced to expand their business to compete with even larger companies, to supply people who buy wool sweaters and ground lamb from enormous box stores. Buy local, and know what you’re buying.)
Either way, this is another one of those horrible consequences of exceeding the Monkeysphere — the sheep have become items, not individuals — and of assembly-lining the process. Forced to do something 1,600 times in a short period, the ranch hands found the fastest, lowest-effort way they could in which to do it. I notice that no-one checked to see if the sheep caught anything from their mouths!