My horse was seen by a vet, we are treating it, but I want to know what yellow discharge coming both from nostril and bleed nose was from?

Hi Cordina, as per your other post, these are questions you really should be asking the vet who's treating your horse. Nobody here can answer your questions safely and appropriately. You do not know the knowledge levels of people here and there is no way to confirm it. I have seen some very very bad medical advice handed out over the internet, and if the person asking the question had heeded some of the advice given, they would have had a seriously ill, or even dead pet. The internet is not the place for medical/vet advice unless you can confirm with absolute certainty that you are speaking with a suitably qualified person.