Hypomagnesemia (Grass, Lactation, & Milk Tetany)

Hypomagnesemia in Goats

(Grass Tetany, Lactation Tetany, Milk Tetany)

by Robert Van Saun, DVM, MS, PhD Department of Veterinary Science Pennsylvania State University

Hypomagnesemia is a common problem in beef cattle on spring pasture, but sporadically seen is dairy cattle and small ruminants such as goats.

Many clinical syndromes have been identified relative to disease circumstances, but all have hypomagnesemia in common. Lactating does on spring pasture are susceptible (Grass tetany or Lactation tetany) as well as growing kids on milk replacer (Milk tetany).

Clinical Signs. Hypomagnesemia (low blood magnesium concentration) usually occurs in early lactation and results in a life threatening disease process characterized by severe tetanic muscle spasms. Affected animals initially show ataxia, stiffness and hyperexcitability. This rapidly progresses into recumbency and paddling. All muscles are overstimulated resulting in extreme leg stiffness and observed muscle spasms. This is very different from the paralytic muscle weakness of hypocalcemia. Convulsions may be triggered by some stimuli including predator attacks, severe weather changes, transportation and other stressors.

Causes. Magnesium is inefficiently absorbed from the rumen. Dietary levels of potassium and excessive calcium can interfere with magnesium absorption. Potassium is especially of concern relative to magnesium absorption. Magnesium also plays a role in maintenance of blood calcium concentrations and hypomagnesemia can induce hypocalcemia. Besides mineral interactions, differences exist between grasses and legumes as to magnesium content. Grasses contain less magnesium than legumes and when growing rapidly in cooler conditions (lush spring pasture), magnesium availability is greatly reduced. Goats like other ruminants, have little ability to manage blood magnesium concentrations if dietary levels or absorption are depressed. The combination of low intake coupled with greater losses during early lactation result in the clinical syndrome.

Treatment. Like hypocalcemia, hypomagnesemia must be treated as an emergency situation. Intravenous administration of combined magnesium and calcium solutions is necessary. This may be followed by subcutaneous injections of magnesium sulfate solutions as well as oral magnesium supplementation. Response to intravenous therapy is rapid, but may be short-lived. Repeat treatments may be necessary. Subcutaneous and oral supplements are useful in preventing relapses.

Prevention. Appropriate dietary supplementation of magnesium from late pregnancy through early lactation is needed. Dietary magnesium should be increased to account for high dietary potassium, up to a point. Dietary magnesium should not exceed 0.4% of dry matter. A suggested ratio of dietary potassium to magnesium of 4:1 is suggested. Magnesium can be supplemented in mineral mixes, but it is unpalatable. Mixing 1 part magnesium oxide, 1 part trace mineral salt and 1 part soybean meal or other palatable feed has been shown to be effective in maintaining good magnesium intakes and preventing disease problems.