Milk fever, also known as hypocalcemia, is often associated with mature dairy cows around the time of calving.
Calcium is taken from a cow’s blood stream as it begins to produce milk and is diverted into the udder.
The cow must then mobilize calcium from its bones to replace the calcium in its blood stream.
A cow’s blood calcium level can drop to dangerously low levels if the process of mobilizing calcium from the skeleton is not efficient.
Calcium is an essential element necessary for muscle function.
As blood calcium drops, the affected cow usually shows signs of muscle weakness and eventually goes down and is unable to rise.
Other symptoms become evident once the cow goes down, such as staring eyes, cold ears, constipation and drowsiness. The heart also starts to beat weaker and much faster.
If left untreated, the low blood calcium will eventually impair the function of the heart muscles and the cow will go into circulatory collapse, enter a coma-like state and die.
Milk fever cases are generally a rewarding experience to deal with as a veterinarian. In most cases, cows will miraculously recover following an intravenous injection of calcium and soon be up on their feet and back to normal.
However, even if they respond well to calcium injections, cows that experience milk fever are more likely to suffer from retained placentas, displaced abomasums and low milk production.
Most of our knowledge about milk fever has been learned by studying the disease in dairy cows.
High producing, heavy milking cows can have a significant amount of calcium enter the udder and are much more likely to be affected.
Older cows aren’t as efficient at mobilizing calcium from their skeleton. As a result, the disease is usually seen in cows older than four years.
Although much less common, we have also seen outbreaks of milk fever in beef cow herds.
The most significant difference is seen in the timing of the disease.
Most beef cows become clinically affected with the disease in late pregnancy.
Nutritionists from the University of Saskatchewan and Saskatchewan Agriculture studied beef herds in northwestern Saskatchewan 10 years ago with the assistance of local veterinarians.
Many of these herds had multiple cows affected with milk fever in late pregnancy and occasionally around the time of calving.
Beef cows that are clinically affected with milk fever seem to be less likely to immediately respond to calcium treatment. This may be because the cases are not identified as quickly as they are by experienced dairy farmers or it may be because of other deficiencies that are occurring at the same time.
Low calcium in beef cows can occasionally be coupled with low levels of blood magnesium, which can cause muscle tetany (spasms) that can also cause cows to go down.
A common theme in the study was that all farms fed a majority of the dry cow ration as cereal greenfeed, mostly from oats or barley.
The cereal greenfeed was particularly high in potassium, which meant the cows ate excessive amounts of potassium. Repeated manure application to soil can cause higher levels of potassium, which then accumulates in feed.
Potassium is a key component of something nutritionists refer to as the dietary cation:anion balance, which affects the cow’s acid base status.
The levels of two important cations, sodium and potassium, are compared to the levels of two important anions, chloride and sulfur.
High levels of potassium can create a subtle change in an animal’s acid-base balance, making it more difficult for the cow to mobilize calcium.
Nutrition researchers see this as a cause of milk fever in dairy cows, and occasionally, in beef cows.
Producers planning to use a significant amount of cereal greenfeed as a winter ration for beef cows should have feed analyzed and consult a nutritionist or veterinarian to help design a feeding program.
Pay particular attention to the levels of potassium in the feed and have a nutritionist calculate the dietary cation:anion balance of the ration. And consider using alternative forages in the critical period six to eight weeks before calving.
John Campbell is head of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.