The transition dip is a deficit that occurs naturally around calving. Calcium is one of the scarce substances and an important one. Nearly all cows have low calcium levels in their blood around calving. When the dip is too deep, problems such as retained placenta, ketosis and infections arise.
The dip in calcium (hypocalcaemia) occurs just before calving. The intrauterine development of the calf requires calcium, but most calcium is needed in the production of colostrum. The common decrease in dry matter intake around calving reduces the intake of calcium around calving.
With increasing parity, cows are more likely to encounter hypocalcaemia. The calcium deficiency is exacerbated by high blood pH, which can be caused by a high potassium diet. High potassium levels in the diet also decrease the absorption of magnesium in the gut, an important factor in maintaining calcium levels.
If the demand for calcium is greater than the supply from feed intake and bone absorption, hypocalcaemia arises. Muscles need calcium to contract.A calcium deficiency increases the risks of dystocia, stillborn calves, retained placenta, ketosis and displaced abomasum.
Furthermore, calcium is needed to activate immune cells. Hypocalcaemia increases the risk of mastitis and other infections.
If calcium levels are too low to supply the skeletal muscles, the cow can no longer stand. This is a typical case of clinical milk fever. However, even a slight calcium deficiency (subclinical hypocalcaemia) will increase the chance on transition problems significantly.