Profitability of milk production is significantly influenced by daily milk yield which related to the average length of lactations or calving intervals in cows in a dairy herd. Milk yield decreases in the end of lactation and income from milk is lower than costs for a „feeding day“. An extension of days open period is a consequence of negative energy balance (NEB) in cows during the first third of lactation. Therefore a restriction of NEB influence, consisting of a preservation of feed consumption and good health of Dairy cows, is for a profitability of milk production key point.