Review/Oorsig Volume 22, Issue 03 - Page 20

Oorsig/Review PART 02 COMMON PRODUCTION DISEASES: MILK FEVER OR PARTURIENT PARESIS Milk fever or parturient paresis Milk fever is a production disease of dairy cows (usually high producing, older cows) that occurs around parturition and the beginning of lactation and that is associated with clinical hypocalcaemia. The name “milk fever” is a classic historical misnomer because in fact most cows with hypocalcaemia have a lower than normal temperature due to reduced muscle tone and reduced circulation. The condition is characterized by an imbalance of blood mineral levels especially low serum calcium; general muscular weakness; depression of consciousness; circulatory collapse and eventually coma and death. Milk fever has quite an interesting history: • • • • • • The condition was first described in 1793 by Eberhardt During the 19th century several descriptions were made of the epidemiology that is still relevant today. Treatments advocated during the 19th century included drenching with various organic and inorganic compounds including boiling ale. Bleeding of susceptible cows before calving was used for prevention, about 5 litres of blood had to be removed. In 1897 Schmidt described a method to treat milk fever that reduced mortality from 40-60% to 10-24%. The method used was insufflation of the udder with potassium iodide and air. It was believed that the condition was caused by a neurological toxin similar to botulism that originated in the udder. In the 20th century it was discovered that the condition was caused by lowered serum Ca levels, and around the mid 1920’s treatment with Ca borogluconate was first started. It was then believed that dietary intake could not sustain Calcium loss through milk production. 20 • • • • Early in the 20th century the role of parathyroid hormone in Calcium metabolism was described, but in the middle of the 20th century prevention was mainly achieved by administering synthetic vitamin D. This at first caused problems with metastatic soft tissue calcification and when the product was improved still only had adequate effect if treatment was administered 3 to 6 days before calving. Since it is not always possible to predict the exact onset of calving, the treatment was later combined with 5mg flumethasone in order to induce parturition. This practice continued into the 1970’s. During the 1970’s and 1980’s changes were being made to dry cow rations to reduce Ca intake in order to “prime” Ca metabolism as was then understood. This is still a viable option today (see later) During the 1990’s and 2000’s Goff and others developed the DCAB theory to prevent milk fever, and this is now widely used in combination with Calcium drenches post partum. Despite the above improvement of our knowledge of hypocalcaemia and milk fever it remains one of the most important and most challenging production diseases in a dairy. Milk fever as a production disease In most cases, hypocalcaemia is caused by a basic metabolism output problem. A fall in serum Ca levels is seen in all adult cows at the onset of lactation. This is assumed to be due to the sudden outflow of Calcium due to the onset of lactation in combination with a failure to rapidly mobilize calcium reserves from bone, and/or to rapidly absorb calcium from the gastro intestinal tract. Phosphate, magnesium and to a lesser extent potassium may also play subsidiary roles. Milk fever is caused by an imbalance in Ca throughput/