Wow. That’s young to wean… Do you have it on calf starter for rumen development? or what is it being weaned to?
I strongly suggest you join the Keeping a Family Cow forum. They have many experienced folks who raise bottle calves. I’ve never done that. They also have several vets who offer free help…
On our homestead, on the few times we have had any respiratory issues, I have used Thyme Essential Oil up the topline and rubbed over the lung area from the withers down toward the front legs. For a calf I wouldn’t use more than four drops.
https://familycow.proboards.com/