As a result of reduced hay yields this year many beef producers are planning to utilize cereal greenfeed as the main forage in their winter feeding program. Greenfeed, if cut in the soft dough stage or earlier, tends to have good levels of crude protein and energy and satisfies the requirements of many rations.
In past years, an increasing number of cattle herds have been exhibiting problems with tetany (a seizure observed as involuntary contraction of muscles) and, in some cases, milk fever. High levels of potassium in the cereal forages used for greenfeed or silage is the cause of this problem. Normally, the level of potassium ranges from 1.5 per cent to 1.9 per cent (100 per cent dry matter basis). Feed tests from cereal forages have indicated potassium levels as high as 4.2 per cent. These same forages tend to have low levels of calcium and magnesium. A ratio has been developed that calculates the potential for the occurrence of tetany. Essentially, it is the total daily intake of potassium divided by the sum of calcium plus magnesium. A value of 2.2 or higher indicates that tetany might occur.
Dry growing conditions and regions where acidic soils (low soil pH) contribute to the accumulation of potassium in plants, especially cereal crops. Tetany can also occur when cattle are fed poor quality hay or straw which have low levels of magnesium.
Symptoms of tetany may start as nervousness, attentive ears and “flighty” cows. Affected animals may avoid the rest of the herd. They may have a stiff gait, poor appetites and urinate frequently. As tetany progresses, the cows may stagger and exhibit twitching on the flanks, ears and face. The animals may lie down and get up frequently. They may be irritable and behave aggressively. After several days, extreme excitement and violent convulsions may develop. At this stage, animals lie flat on their sides, their forelegs pedal frequently, saliva flows freely, breathing is laboured and the pulse is rapid.
If treatment is not administered at this stage, animals die during or after a convulsion.
Older cows are more susceptible than first or second calvers because of lower magnesium stores and decreased absorption efficiency. Tetany often strikes when cows start to freshen or in the early stages of lactation. High producing cows are particularly susceptible. Dry cows and bulls are rarely affected.
It is important to ensure the cows are receiving adequate levels of calcium and magnesium. A feed analysis will indicate the levels of available nutrients and minerals in the greenfeed or silage. Based on the results of the feed tests, proper mineral and vitamin supplementation can then be provided.
Producers should contact their veterinarian if cows exhibit signs of tetany. Livestock nutritionists can assist in developing proper magnesium and calcium supplements to prevent or treat tetany problems.
Good results have been obtained by supplementing with two to three ounces of limestone and one ounce of magnesium oxide. Often, the addition of limestone is all that is required to prevent this condition.