We have been raising a few beef calves for about 5 years now. We never had any problem until this year. We have just lost our second calf in about 2 weeks. They are fine one day and the next thing you know they are laying there dead. Any clues? They have access to hay free choice and a barn. They were born in the spring, so they are not super young. There is always a source of water as we have a stock tank heater. Thanks for any help you can give.