Yes this has been discussed before. I think the consensus is that “death” is not specific enough. A “birth” log represents the start of an animal asset’s lifespan, in the same way that a “seeding” log represents the start of a plant asset’s. How these assets end their lifespan will vary. For animal assets, maybe it was due to illness, or maybe it was slaughtered. One might be an observation, and one might be an action.
Here are some older discussions for context/reference:
@wotnak created a module called Asset Termination, which is a nice flexible solution. It allows you to record a log (of any type) that “terminates” any assets referenced by it. See the last link above for more information.
There is some discussion about adopting that as a core convention in farmOS, but for now it is available as an add-on module.