My neighbor's heifers are in the pasture next to us (b/c we watch them for him). The first one to calve had twin heifers, 3 weeks ago. Both are doing just fine - that is until last weekend. He fed hay on the other end of the pasture and one calf slept while the others went to the hay. She stayed where she was all day, night and the next morning, bawling every so often. Momma had the other calf and didn't think about this little one, but my cows were sure concerned. :D
We caught the little one and used the ATV to haul her over to the herd, where I'm sure she found something to eat.
Both calves are growing equally well and are keeping up with the other calves that were born a few day later.