Many thanks Melinda and Caro, that's all really helpful. I'll mull it over and digest what I can (pun intended
). Yes, the vet had suggested watering Nutri-gel down with water, which I would tube in, but I was also concerned about the amount of sugars there might be in it, and you have both brought that point up.
I hadn't considered baby food, and that is something I can get here, so that might be worth a try. The vet had also suggested supplementing with children's vitamins.
I only rear the chickens for 2 weeks, in an indoor enclosure, and feed them commercially prepared dry pellets (and sometimes rice) so unless the pellets contain lung worm eggs (which is not impossible I suppose, no idea exactly what is ground up to make them) I don't see how they could be contaminated. Would worms cause mucus or just lung damage? This is definitely soft white mucus he "coughs" up, not a worm body.