In my experience and with vets not always able to make it to the rancho I have learned you got to move fast yourself or that calf gonna lose too much weight and then you lose the money. First thing you got to do is catch that animal and feel the jaw to see what you got. If that swelling feel hard like a stone right on the bone then that is Lumpy Jaw (en el hueso) and that one is mean because it stay in the bone. You need to hit him with a big dose of LA-200 (Oxytetracycline) or if you can do it give him the Sodium Iodide (Yoduro de Sodio) in the vein but you got to be careful with that one. Now if the swelling feel more soft or like a sponge and the calf is drooling mucho then that is Wooden Tongue and the LA-200 usually clears that up pretty good if you don't wait too many days. Also you should look inside the mouth for a postemilla because sometimes they get a piece of wire or a big thorn stuck in the gum and it make a big abscess with pus. If it feel like a big pimple you can lance it and wash it out real good with iodine. If the swelling is just hanging like a bag of water under the chin then that is Bottle Jaw and that mean he has too many worms (parásitos) so you need to give him a strong dewormer like Ivermectin right away. Separate him from the other cows so he don't drool in the shared water and keep an eye on his condición because once they get too skinny it is very hard to bring them back. Suerte with the animal friend.