I spent a month in India earlier this year with a retired Indian vet who had a wealth of information about the medicinal uses of lots of different Indian plants. His absolute favourite was the Neem tree. It is reputed to be extremely good for all sorts of ailments and is higher in protein than a lot of the vegetation that the local animals would normally eat. I tried some of the leaves and it is extremely bitter so I'm quite sure that most animals wouldn't eat much of it and then only when it is mixed with more palatable food. The Indian vet also was quite adamant that the oil was only for external use as it would be toxic if consumed, but the leaves were alright to eat in small quantities.