In article , Mary Fisher
writes

We avoid
them on animal welfare grounds,

Why is that? hoof and horn and even blood are products of the
slaughterhouse, animals are slaughtered for food. I'm not challenging, just
asking.

It goes back to our goat-keeping times. A lot of our goat milk went to
people with allergies to bovine produce. Health advisers pointed out
that some problems could arise from bovine animal blood or bone nasties
entering the food chain through the herbage and then into the milk. We
don't need to use that kind of fertiliser anyway because we have plenty
of organic compost - partly made from stable and farmyard manure!
--
Alan & Joan Gould - North Lincs.