For early calving herds, the risk of tetany may be low, but for those that are calving or will soon be, now is the time to consider how to manage this deficiency, which can lead to death.
The Condition
Low blood magnesium (hypomagnesemia) is a complex metabolic condition aggravated by stresses such as lactation, weather, fatigue or excitement. Consumption of forages such as lush grass pastures or green cereal crops (cover crops) in which magnesium is low can reduce blood magnesium and precipitate the highly fatal crisis called tetany. Adult lactating animals are most susceptible because of the loss of Mg in milk and their inability to mobilize Mg bone reserves. Tetany usually occurs near parturition and/or until approximately 2 months postpartum, and the frequency usually increases with older cows. It is rare in non-lactating animals unless they were undernourished and turned into lush pasture or a green cover crop. Cool, rainy weather can increase the incidence of this disease.