Changes in Serum Magnesium Levels of Ruminants, as Influenced by Abrupt Changes in the Composition of the Diet Effect of Oral Administration of Various Inorganic and Organic Compounds on the Serum-Magnesium Level

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Abstract
During a period of four years in succession samples of grass from tetany prone pastures, topdressed with large amounts of amraon-sulphate and potassiumsulphate, have been analysed throughout the tetany season each year, and the results have been compared with the analytical data obtained from corresponding samples of grass collected from normally dressed pastures. The content of Mg and Ca and the feed unit value of the tetany prone grass differed very little from the normal. The protein content, however, was exceptionally high, and rather great differences were found in the content of P, S, K, Na and the trace elements. Several feeding experiments have been carried out in order to test the hypomagnesaemic and/or the tetanygenic effect of these compounds as dietary supplements to ruminants. The feeding was performed under exact daily control and the experiments were supported by daily serum mineral analyses. Experiments carried out with diets containing protein and feed units in the same ratio as found in the highly topdressed pasture grass, proved that this unbalanced ratio undoubtedly played an important role in the hypomagnesaemia inducing effect of the grass. As long as the fodder was given in amounts high enough to cover the feed units requirements, the level of serum Mg remained unchanged. The falling tendency of the serum Mg level was, however, evident when the fodder rations were reduced to amounts insufficient to cover the feed unit requirements ot the cows — a situation often met with for shorter periods during pasturing. Hypomagnesaemia was produced within 3–4 days, whereas a similar reduction of a normally balanced fodder to cows had no serum Mg reducing effect in the course of twelve days. Of other factors coming into play, especially K2HPO4, Na2HPO4, K2SO4 and Na2SO4 proved to influence the serum mineral balance. Oral applications of large doses of these substances to healthy sheep, produced neither pronounced hypomagnesaemia nor tetany. The initial drop in the levels of serum Mg and particularly serum Ca were, however, so remarkable that tetany very probably would have been provoked if the animals had been in a hypomagnesaemic state when the experiment started. Experiments and results have been closely discussed. The conclusion has been drawn that the tetany prone effect of the heavily ammonsulphate dressed pastures could not possibly be conditioned by one single factor in the grass. A more possible explanation seems to be an unpropitious interaction of more active compounds present at the same time: The first step in the development of the disorder, i. e. the hypomagnesaemic condition, seems principally to be due to the unproportionately high content of protein in relation to the feed unit value of the grass. Owing to the fact that the quantity of dietary protein is in excess even if the feed unit content does not cover the theoretical requirements, the milk production remains high and the cows are hampered in their efforts to accomodate to those reductions in food intake unevitably happening to occur on pasture. The next step, the convulsion of tetany, however, depends upon other, co-operating factors able to disturb the Ca-balance at the very moment when the serum Mg is already low. According to the serum Mg- and Ca-reducing effect brought about by diets supplemented with alkaliphosphates and -sulphates, the author incline to the view that the extremely high content of P, S, K and to some extent also of Na found in the tetany prone pasture grass, may be the background for this effect of the grass. Temperature, rainfall and other environmental factors have also been taken into consideration as influencing the appetite and the absorptioncoefficient.