The postpartum period is a critical stage of lactation for a high producing dairy cow. This period is characterized by drastic metabolic changes, immunosuppression, negative energy balance (NEB) and elevated levels of stress, which can lead to increased incidence of diseases and decreased animal efficiency. Ketosis is one metabolic disease, frequently observed in high producing herds. Ketosis usually occurs within a few days to a few weeks after calving. It is characterized by low blood glucose, excess ketone bodies in blood and urine, lack of appetite, either lethargy or excitability, weight loss, depressed milk production and occasionally, in cases of severe ketosis, incoordination and neurologic signs. Based on various reports, the incidence of clinical ketosis can range from 2 to 15% and subclinical ketosis from 9 to 34%.
Any factor resulting in a reduction of dry matter intake (DMI) increases the risk for ketosis. Around calving, lactating dairy cows naturally decrease DMI due to the advanced stage of gestation, as well as metabolic changes which occur in this period. This decrease in DMI typically leads to NEB. During the last week of fetal development, the fetus uses approximately 46% of maternal glucose. The onset of milk production makes this energy shortage even more remarkable. When lactation starts, the mammary gland requires a large amount of glucose for lactose milk synthesis. It is estimated that the mammary gland consumes 60 to 70% of the whole body glucose, mainly for lactose synthesis. In this case, a cow producing 66 pounds of milk per day uses at least 3.3 pounds of blood glucose to synthesize milk lactose. The high energy demand during this period of glucose shortage triggers a compensatory process of nutrient partitioning and fat mobilization. During this period of glucose shortage, fat is mobilized as an alternative source of energy. It is used as a fuel for basic cell functions in addition to providing energy to maintain milk production.
In the process, ketone bodies are produced and the excess are eliminated in the urine and milk. Several studies have described deleterious effects of ketosis on animal health and reproduction. Clinical ketosis is associated with an increase of 2 to 3 days to first service and a 4 to 10% reduction in pregnancies per AI at first service. Other researchers have identified an association between ketosis and an increased incidence of ovarian cysts. Body condition score (BCS) has been linked to metabolic changes during the postpartum period. An elevated BCS at calving is a major risk factor for ketosis.