Im rembering a part in James Harriet's book where he visited a farm for something unrelated & there was i think a ewe dying in a corner & James said he didn't think she'd make it & told the farmer to put her down He said he'd let nature take its course So Harriet snuck some pain killer to the poor animal & she slept for 3 days & then recovered
The idea that animals are better with pain is a very old school thought and it's becoming a best practice for vets to prescribe pain medication after surgeries.
Majority of animals hide pain and work themself to death to make owners happy, others are absolute babies and if they are sore they limp for days, which I'm glad my horse is an absolute baby so we can get stuff checked out instead of hiding shit