I'll combine them if you don't mind, Amigo as you have the same question.
Little tan calves. After they're weaned [taken away from their mothers] and put on straight feed, no milk, they can get sick from the combination of cold weather, stress from being weaned, new kinds of food, different water, no water, the experts say there are a lot of different reasons..
Two of my tan calves, out of four or five tans, seem to bloat from the alfalfa/brome hay I put them all on. Bloat is bad gas in their stomach, that they can't get rid of naturally. All cattle produce gas, but most are able to belch and fart it away.
Unless the gas is removed the animal will die, so I put a 1 foot by 1inch plastic tube down the calf's throat, then I feed a 6 foot by 1/2 inch tube thru the 1 inch tube down into their stomach. The bigger 1 foot tube is hard so it protects the soft tube so that the calf can't bite thru it. When you've shoved the right length down an you hit the right place, the gas comes whooshing out of the tub and their drum like stomach deflates like a balloon.
Oat straw is tasty but it doesn't have much food value so they get calf pellets, a commercial blend of all the right food, minerals and essential nutrients.