Dec. 15, 1924 
Composition of Diet, Blood, and Milk 
619 
It is necessary also to bear in mind 
certain evidence, which will be re¬ 
viewed briefly at this point, that 
indicates that the secretion of milk 
may be affected through either the 
precursor of milk fat or that of milk 
protein. This evidence gives some 
idea of the differences in the changes 
that occur in the composition of 
milk when its secretion is affected by 
these different precursors. 
Morgen and a number of his col¬ 
laborators have conducted an extensive 
series of experiments on sheep and 
goats in which the effects on milk 
yield of varying the protein and fat 
of the diet were studied (13-16). 
The plan of the experiments was to 
in the composition of the milk; changes 
in the dietary fat, when they produced 
changes in milk yield at all, generally 
changed the concentration of milk fat 
in the same direction as the change 
made in the dietary fat; and the 
concentration of milk nitrogen, in the 
opposite direction. It seems likely 
that the changes in the composition 
of milk produced by changes in the 
quantity of dietary fat would have 
been even more regular than they were 
had they been determined immediately 
instead of after an interval of some 
days. The concentration of lactose in 
the milk was not significantly affected 
by any of the dietary changes studied 
in Morgen’s experiments. 
0s4YS 
Fig. 5.—Experiments VII and VIII. Effect on milk yield of change in quality of dietary protein. The 
yield before the ration was changed is taken as 100 per cent 
change the rations by substituting 
protein or fat for an isodynamic 
amount of carbohydrate, or vice versa, 
and then, after an interval of some 
days, to determine the effect which 
had been brought about on the yield 
and composition of milk. It was 
found that milk yield could be affected 
by such changes in either the protein 
or fat of the ration. Changes in the 
dietary protein affected the milk yield 
through a wide range in the level of 
the protein feeding; changes in the 
dietary fat, on the other hand, only 
when they were made at low levels of 
fat feeding. Changes in the dietary 
protein produced only irregular changes 
Subsequent to Morgen’s work, an 
extensive series of experiments, in 
which the effects of dietary changes in 
fat on the yield and composition of 
cow’s milk were studied, was made by 
the Deutscher Landwirtschaftsrat (4). 
The results of these experiments indi¬ 
cate that the dietary fat has less effect 
on milk secretion in cows than it has 
in sheep and goats. But an experi¬ 
ment reported by Jordan and Jenter 
(9) indicates that, under appropriate 
circumstances, milk secretion in cows 
may be affected by changes in dietary 
fat and that, when it is so affected, the 
concentration of milk nitrogen varies 
in a direction opposite to that of the 
change made in the dietary fat. 
