weird behavior is also a clue...we have been hand feed big squares of hay & a little grain each day, I take a good look at them each day. so heres some examples:
The night before the first cow calved, she waited outside for several minutes, until all other animals in the barn and settled down--was just weird, she didn't want to get in the pushing match, also I think she was waiting for the 8' snow and sleet storm that was coming. Our second cow to calved this year, again waited for the cold front and blustery, snow and wind weather and calved friday night. Friday when we fed she waited outside on the hill for a long time, then decided to come in barn a few minutes, then went to the side of the barn and moo'd real soft..was really wierd behavior. I'm now waiting on a first calf heifer..she is soo loose and looks like anyday for a week..wonder what wierd behavior she will exhibit.
Good Luck!