I was talking to a farmer during the week who said his in-calf heifers were licking the lime on the cubicle beds. He had given the heifers a mineral bolus but they weren’t getting any dry-cow minerals.
Most boluses only cover trace elements, so supplementary magnesium, phosphorus and sodium are not being supplied by these. If sodium was deficient the heifers would likely be drinking urine, so it could be a magnesium or a phosphorus problem. A deficiency in either needs to be rectified fast. The magnesium requirements of pregnant animals doubles in the last two weeks before calving. Magnesium is an important mineral for muscle function, so it helps at calving and for pushing out the cleaning. So make sure your herd is covered for the major elements and not just the trace elements. Some farms are having a hard time with milk fever in fresh calvers. Insufficient calcium after calving is a factor, but so too is feeding silage high in potassium (K) before calving. If you have a problem get your silage tested and try to feed silage low in K to dry cows.