Cattle producers faced many challenges with forage and crop production last year. Many areas had poor hay crops and the weather didn’t co-operate at harvest for many grain crops.
As a result, many beef cattle herds have relied heavily on baled cereal crops, such as oats or barley, as a major component of their winter rations.
This greenfeed, when it’s of good quality, is a great option for wintering beef cows but it can be associated with a metabolic disease known as milk fever or hypocalcemia.
Milk fever or hypocalcemia is a disease often associated with mature dairy cows around the time of calving. As the cow begins to produce milk, calcium is taken from her blood stream into the udder. The cow must then mobilize calcium from her bones to replace the calcium in her blood stream. If the process of mobilizing calcium from the skeleton is not efficient, the blood calcium level of the cow can drop to dangerously low levels.
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.
Once the cow goes down, other symptoms become evident 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. An injection of calcium intravenously and, in most cases, the cow will miraculously recover and soon be up on her feet.
However, even if the cow responds well to calcium injections, cows that experience milk fever are much more likely to suffer from retained placentas, displaced abomasums and other complications including lower milk production. Cows that are down because of milk fever, for any period of time, also have the potential to suffer from muscle damage, which can make their recovery problematic.
Most of our knowledge about milk fever has been learned by studying the disease in dairy cows. These 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 and usually the disease is seen in cows older than four years. Most dairy producers, veterinarians and nutritionists manage the dry cow diets carefully to prevent this disease.
Although much less common, we have 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 and less commonly after calving, which is more typical in dairy cows.
Cases are usually diagnosed by seeing a cow having difficulty standing in late pregnancy and then by having your veterinarian take a blood sample to analyze blood levels of calcium, magnesium and phosphorus. Most veterinary clinics have the capability of doing the laboratory work for those blood samples within the clinic and can usually confirm the diagnosis within a few hours. Responsiveness to treatment with calcium is also an important diagnostic tool.
A number of beef herds were studied in northwestern Saskatchewan more than a decade ago, by nutritionists from the University of Saskatchewan and Saskatchewan Agriculture, with the assistance of local veterinarians. Many of these herds had multiple beef cows affected with milk fever in late pregnancy and occasionally around the time of calving. These herds tended to be composed of cows with relatively high milk production such as Simmental breeds.
Beef cows that are clinically affected with milk fever seem to be less likely to respond to calcium treatment immediately. This may be because the cases are not identified as quickly as they are by experienced dairy farmers or it may be due to other deficiencies that are occurring at the same time. These cases of low calcium in beef cows can occasionally be coupled with low levels of blood magnesium, which can cause muscle tetany (or spasms) and that can also cause cows to go down.
A common theme was that all farms fed a majority of the dry cow ration as cereal greenfeed. In this particular study, the farms were mostly using greenfeed from oats or barley. The cereal greenfeed was particularly high in potassium and as a result, the cows were consuming excessive amounts of potassium throughout the wintering period.
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 or DCAB. This dietary indicator actually has an impact on 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 the acid-base balance in the animal, making it more difficult for the cow to mobilize calcium. This relationship has been well described by nutrition researchers as a cause of milk fever in dairy cows and it appears to also be important in beef cows.
If you have fed a significant amount of cereal greenfeed as a winter ration for your beef cows, you may want to be aware of the potential of hypocalcemia in late gestation beef cows.
It is not a syndrome that we usually look for and therefore can sometimes be missed in the early stages.
You might also want to consider using alternative forages other than greenfeed in the critical period six to eight weeks before calving.