Hi,The chill may be to do with the upset stomach, make sure to keep the sick ones warm and seperate from the healthy lambs, as these things spread so quickly. If they are cold wool lamb covers available in nz from farm gear retailers can help keep them warm, I expect you will be able to get these . Make sure also that the bedding (hay?) is dry and no draughts. Check too that they dont have watery mouth- wet and mucusy around the nose and mouth, this often goes along with being chilled.