Ketosis or milk fever is a metabolic disease in which a cow finds itself in a negative energy balance. Ketosis occurs when cows consume too little feed immediately after calving compared to the amount of milk produced. The energy intake is lower than the energy requirement, resulting in a glucose deficiency. As a consequence, the cow breaks down its fat reserves to provide energy. The liver then cannot completely break down all fatty acids, so that ketone bodies are produced. The ketone bodies get into the blood, urine or milk. Large concentrations of ketone bodies are toxic. A distinction is made between clinical and subclinical ketosis. When it comes to clinical ketosis, the symptoms are immediately visible. Symptoms are not (yet) observable in subclinical ketosis.