Any animal that needs a vet will either get taken to or visited by the vet, or get the knackerman calling - it'll not be left to suffer. So we still have the vet bills to pay in the first instance - but an older girl who's had problems this year will probably struggle next, so it's best for her and for us if she's away when she's fit. Depending on the problems she's had, a younger animal may be given the benefit of the doubt and kept on.
With cattle especially these decisions are not taken lightly, but BH reckons for every 5 he's kept on against his better judgement, he's had 4 suffered the following year. And watching a beast struggle doesn't make him feel like a good stockman, so that strengthens him for these difficult decisions.
Whichever road one takes, all such decisions are made with the best interests of the animal very firmly in mind, whether you are a farmer with hundreds of stock or a hobbyist with a handful.