Body builders that push themselves too hard swear by this stuff to reduce their down time but I don't know how much of that is psychological. Body builders use BPC-157 injections for tendon repair [0]. It's also banned in horse races and banned for humans by WADA as it is considered cheating. Here [1] is an example of people trying to figure out if someone is cheating. Perhaps there are more studies on nih.gov by now, Ill check. All the cases I have seen thus far were for race optimizations and not treating old mares with a bum leg.

[0] - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6271067/

[1] - https://pubmed.ncbi.nlm.nih.gov/23084823/