210             Hypomagnesaemia in Heifer Calves

sufficient for maintenance. Wendt [1925] offered as a standard 0.01 gm. of
magnesium per kg. of body weight, which amounts to roughly 4.0 gm. of
MgO per day per animal of 500 lb. live weight. Forbes, French and Letonoff
[1929] found that on a ration of equal parts of maize meal and alfalfa hay at a
level of half maintenance, storage of magnesium occurred with an intake of
9 mg. per kg. body weight. At the same time, these workers observed a
negative retention of the mineral when alfalfa hay alone was fed at main-
tenance level, although the magnesium intake in the later experiment was as
high as 32 mg. per kg. of live weight. Using a basal ration largely or entirely
composed of milk, Huffman and Duncan [1936] were able to maintain the
magnesium content of blood plasma by administering extra magnesium com-
pounds to the extent of 15 to 20 mg. per lb. body weight. If the figures given
in Table IV are represented graphically (Fig. 1) it will be noticed that with a
feed consisting of grain-mixtures and wheat straw the minimum daily magne-
sium requirement works out at 24 mg. of MgO per lb. of body weight. This
figure is twice as high as that given by Wendt [1925] or that found by Forbes
et al. [1929] on the maize and alfalfa diet. Our figure, however, compares
favourably with the figure of Forbes et al. obtained from the alfalfa alone
feeding experiment or that of Huffman and Duncan (loc cit.).

[NLS note: a graphic appears here - see image of page]

FIG. 1. Relation between feed magnesium concentration and magnesium retention