| |
During the past few years, an increasing number of cattle herds are exhibiting problems with "winter or grass tetany" and in some cases, milk fever. Winter tetany is a metabolic condition caused by lower than average blood magnesium levels. It is seen in cows in late pregnancy or after calving. Signs of grass or winter tetany in the cowherd are often a dead cow or cows with marks of struggling or paddling on the ground around head and legs. Cows that have not died are often excitable, uncoordinated, trembling or staggering. Occasionally, affected cows look like those with milk fever in that they are down, very quiet and unable to get up. Older cows are more susceptible than first- and second-calvers because of lower magnesium stores and decreased efficiency of absorption of magnesium from the gut. Dry cows and bulls are rarely affected. Producers should contact their veterinarian immediately if their cattle show any of these symptoms. Treatment may include intravenous or subcutaneous administration of solutions containing magnesium and calcium salts.
Winter tetany in Alberta and across the Prairie Provinces is often associated with feeding grain, straw or greenfeed rations. Cereal feeds are low or borderline in magnesium compared to the cow's requirements (gestating cows need 0.12% and lactating cows need 0.20% Mg of dry matter intake). Also, high levels of potassium in feeds can reduce the amount of magnesium that is absorbed from the diet.
Repeated or high levels of manure application to soil can cause high accumulation of potassium in feeds. Dry growing conditions and regions where acidic soils exist (low soil pH) contribute to the accumulation of potassium in plants. Normally the levels of potassium in feeds range from 1.5 to 1.9% on dry matter basis. Feed tests in Saskatchewan in cereals grown in 2001 indicate potassium levels as high as 4.2%. Similar results are being reported in Alberta. Gestating cows need 0.6% of dry matter intake as potassium and lactating cows need 0.7% potassium. Indeed, the maximum tolerable level is 3% of dry matter intake. Thus, the high dietary potassium reduces absorption of magnesium from the gut of the cow and also reduces the efficiency with which calcium is mobilized from the bone for productive purposes by the cow.
Prevention of this condition is possible through supplementation of the diet with magnesium oxide and limestone. Limestone is a source of calcium. Supplementation programs should be designed to provide approximately 40 grams of magnesium oxide and 80 grams of limestone per cow per day. Greater amounts may be required if the potassium level in the diet is very high. Magnesium oxide is very unpalatable and needs to be mixed with grain or screening based supplements to achieve this level of intake. Producers should work with a nutritionist from a feed company to design a program that fits with their management program. The goal should be to reduce the K/(Ca + Mg) ratio to less than 2.2 in the diet. Levels of the K/(Ca + Mg) ratio greater than 2.2 indicate a potential for winter tetany in your herd. The nutritional program should also aim to get the Ca:P ratio to greater than 2 in the total diet. Cereal-based rations also require supplementation of salt, trace minerals and vitamins and, if a lot of straw is used, protein.
For additional information contact Bryan Doig, Livestock Agrologist, Saskatchewan Agriculture & Food, North Battleford, SK at 306-446-7477 or Tennis Marx, Beef Specialist, Alberta Agriculture, Food and Rural Development at 780-653-5130.
Grant Lastiwka, Pasture Agronomist, Western Forage/Beef Group, comments:
We are finding in central Alberta and other areas of the province that tetany is also occurring. The minerals taken in by animals in their drinking water also affects the situation, positively or negatively. As Brian has said, the calcium/magnesium imbalance has the greatest likelihood of occurring just before or during calving in the form of tetany or milk fever. Cases may be visible by finding a dead cow that was calving or laying on her side in a slight hollow. These could be misdiagnosed as calving difficulty or weak cow syndrome.
If your feed samples were analyzed, ask yourself, "Were they properly collected and are you comfortable that it is a representative sample of what you are feeding?" Check to see if you have analyzed for calcium, phosphorus, potassium and magnesium.
Do you have a water analysis you can provide to your nutritionist?
Check to see if your feed analysis was done by the more costly, wet chemistry or the cheaper Near Infrared Reflectance Spectroscopy (NIRS) method. In the NIRS method the mineral analysis is less accurate than a wet chemistry mineral analysis and should be used only with great caution.
Finally, if you are now providing the necessary mineral package to the animals' free choice, are their intakes at the recommended levels? Calcium is not palatable and magnesium is very unpalatable. If feeding a free choice mineral mix, add flavoring agents and a 58% granulated magnesium oxide for best results. Granulated gets better intake than other more powdery magnesium forms.
Monitor the intakes to see that they are meeting recommendations. Manage the location and freshness of the mineral.
If intakes are still low, you are concerned and have not had a feed analysis done, you may want to force feed 1-2 ounces of magnesium and some additional calcium in a grain ration. This is a much more preferred method for feeding minerals.
Force feeding 1 ounce of magnesium oxide if the problem is just a magnesium deficiency works well or, up to, but no more than 2 ounces if the ration also has an excess of potassium. To compensate for the excess of potassium affecting calcium and magnesium absorption (called the DCAB ratio - we lack good information on DCAB critical values in beef cows) the feeding of calcium and magnesium needs to be higher than recommended.
Consult a nutritionist, beef specialist or livestock specialist for more details.
The contents of this page are no longer available.
|
|