Health events are undesirable events in dairy farms, and in my opinion, are one of the biggest challenges the dairy industry has been facing. Although the incidence of some specific diseases, such as milk fever or clinical ketosis, has decreased in the last 20 years or so, the overall percentage of animals experiencing one or more diseases in the first 60 days after calving hasn't changed.
If we start from the basis, a sick animal has impaired welfare since optimal health is a key component of animal welfare. Furthermore, diseases require costly interventions to treat affected animals and represent an important economic loss for the farm. Nevertheless, the biggest economic loss associated with animal diseases is not the cost of treatment, but the loss in animal performance and the higher chance of being culled.
Diseases can be defined as a deviation from an animal's tissues or cells' normal functions or structure that can be caused by a pathogen or metabolic disturbances, among others, and that is often associated with clinical signs or subclinical findings. This definition matches common dairy cattle diseases such as mastitis, lameness, and hypocalcemia. However, in dairy cattle, we have a broader term to refer to health issues, which is health events. A health event is slightly different from a disease since the term includes animal losses, such as stillbirth, short-length events, such as dystocia, and undesirable events that have been associated with poor performance, such as twin births.
Regardless of the definition we used, these undesirable events have been associated with poor animal performance and lower longevity. Considering that 35-40% of dairy cows in the U.S. develop a health event in the first 60 days in milk, the latter is very relevant, and preventing disease should be the focus of any animal management program. The initial loss in performance is usually seen in milk yield since one of the primary signs of clinical disease in dairy cattle is a drop in dry matter intake and milk yield. On top of this, the veterinary treatment bill adds to the overall short-term loss of the disease. It has been estimated that common diseases such as clinical ketosis and lameness cost the farm between $145 and $400 per case.
Source : psu.edu