A veterinarian may administer a magnesium solution intravenously, as soon as possible. Frequently, treatment can be given in range conditions. The response to treatment depends heavily upon how advanced the condition is at the time of administration. Animals that have been down for 12 hours or longer are poor candidates for successful treatment; muscle damage may prevent these animals from rising even if their magnesium status is corrected.
Treatment is often complicated by the severe nature of the animal's convulsions and potentially aggressive behavior; practice caution to avoid being injured.
An intravenous solution containing magnesium (as borogluconate or chloride salt) and calcium is the treatment of choice. An intravenous dose of 1.5 to 4 grams of magnesium is necessary to correct the magnesium deficit. Depending on the product used, a dose of 500 to 750 ml will achieve that level. Solutions should be administered slowly. Animals should be left alone for 30-60 minutes following treatment before being stimulated to rise. This will allow time for magnesium concentration in the cerebrospinal fluid to return to normal, while avoiding the possibility of inducing further convulsions. Relapses following the first treatment are not uncommon.
Read the full description and recommendations for grass tetany prevention by Cody Wright, PhD, Eric Mousel, PhD and Russ Daly, DVM, here.
Source: South Dakota State University and Bovine Veterinarian (sister publication to Dairy Herd Management)