Bloat is a condition where the lamb is unable to belch up the gas which is formed in the second stomach (rumen). The pressure will build up until it interferes with the lambs breathing and heart and he can die. It is caused by certain alfalfa hays, clover and alfalfa pastures.
The lambs abdominal area (belly) will be very swollen looking, particularly on the left side. The left side will often be higher than the top of the back. The lamb will be uncomfortable and depressed. This is an emergency situation. You need to get the lamb to the veterinarian as soon as possible.