This review article focuses on negative energy balance (NEB), which occurs in dairy cows especially in the early lactation. The NEB is a condition in which dairy cows expend more energy than they are able to receive from feed, which has a significant impact on their overall health and reproductive performance. The article discusses in detail the complex metabolic processes that take place in a dairy cow during NEB. Furthermore, the article addresses how NEB affects the health status and reproductive performance, which has a direct impact on overall farm efficiency. Various methods of using direct and indirect indicators are described for early identification of NEB and associated health risks that can be monitored in practice. The article concludes by highlighting the importance of further research in this area, particularly with the aim of developing more accurate and reliable diagnostic tools to enable farmers to monitor the health status of dairy cows and minimise the negative impact of NEB.