A study of the methods of controlling the incidence of hypomagnesaemia and hypomagnesaemic tetany in ruminant animals

The disorder of magnesium metabolism resulting in hypomagnesaemi and tetany is one of the most troublesome metabolic disturbances discussed and studied in the last thirty years. It is not known to occur in human subjects or in domestic pet animals, but it occurs in ruminant animals, particularly bovine (13). It affects cattle (1,12,30,41,89 h sheep (19, 75, 78 ), young calves - reared on Bilk alone or milk with various supplements (17, 32, 51 53, 53 ) - and it has been artificially induced in rats by a deficient-magnesium diet (51). It is not confined to any particular sex, age or breed (2). It is generally accepted that the eai"liest cases of tetany on record occurred in the 1920 s. Since then numerous other, outbreaks have been reported from 'European countries, Australia, Hew Zealand and certain parts of the U.S. The earliest detailed observations of these occurranoeH, however, were made in the period 1929-1930, when Sjollema and Seekles (89) and Sjollema (90 discovered that low-blood magnesium values were a significant biochemical feature of tetany. Since then a great deal of work has been done on this subject and and a number of explanations have been offered, ¡dost of these involved the following two approaches: (1) Hypomagnesaemic tetany was regarded as dysfunction of the physiological mechanism controlling the level of blood-magnesium. The mderlying cause was thought to be inherent in the animal itself with environmental stresses permanent (41). (2) Hypomagnesaemic tetany was regarded as being of complex dietic origin in which the excess of certain essentials in the feed such as protein (91) and potassium (85) were involved. No single specific factor has been successfully identified as the causative agent in hypomagnesaemic tetany, and in spite of the work of several investigators in many different countries seeking an explanation to this disorder, the primary cause is still unknown. Further, the nature of the physiological mechanism which controls the level of blood-magnesium is still not understood (2, 10 11,41,100). The disease appears to be increasing every year but whether this increase is a real increase or only an apparent one due to better diagnosis, is not known (61)« During the last 15 years, the disease has spread (97). It has affected '• tetany-free“ areas and and the conditions under which it occurred in the past have apparently changed. It occurs in dry cows (30,96) and in stall-fed animals in winter which are given hay and concentrates, as well as those on pasture (2,14,41,65,66,86,100 ). Today, tetany is a serious economic factor and its spread and increase are regarded with considerable anxiety. Hopkirk et al. (45) state that, “death rate from tetany is extremely high, but the percentage incidence of the disease to the cow population is comparatively low.” Sjollema (94) pointed out that mortality from "grass tetany” is much higher than from' cases of acetonaemia and milk-fever