Hi, I have goats and I have had good results with feeding them fresh plants that would help a particular issue and have also given them tincture by squirting a little in a some grain. For respiratory issue, you could
feed them some wild blackberry leaves, wild
rose hips (anti-viral) lemon balm, onion, chives, you could even see if they would eat echinacea flowers. Animals are pretty close to the earth and so know what they need. I don't know about mullein, you could try that but that isn't one of the ones I would choose first off. With tinctures, I have given them Echinacea, wild rose and St. Joan's wort.
Glad to hear they are feeling better.
Peace, Julie
www.crowsdaughter.com