INFLUENCE OF THE PLANE OF NUTRITION UPON MILK 71 
portance of controlling the plane of nutrition of the 
cow becomes especially apparent in studying the influence of 
specific feeds on the composition of the milk fat, in which 
the changes in the ration which are necessary for studies of 
this character may bring about a temporary underfeeding 
of the cow. The great care which it has been found necessary 
to exert in studies of this character at this Experiment Station 
to avoid involving the effects of underfeeding with the effects 
of specific feeds throws great doubt on the results of many 
of the studies of this kind that have been published in the 
past. Not only is it necessary to control this factor in feeding 
studies, but it is also necessary to take it into account in the 
interpretation of the results. The data secured in the under- 
feeding studies are also useful in explaining some of the 
heretofore unexplained cases of abnormal butter that are 
occasionally reported in the agricultural literature. 
Application to feeding experiments. The danger of 
allowing the effects of underfeeding to interfere with the 
correct interpretation of the effects of specific feeds on the 
composition of the milk fat is no more strikingly shown than 
in experiments to determine the effects of fresh pasture grass 
on the composition and properties of butter fat. Not only is 
there danger of a cow in good flow of milk being underfed if 
suddenly turned from dry feed to pasture, but more or less 
underfeeding is practically certain to follow such a procedure. 
This is due to the relatively low nutritive value of fresh 
pasture grass together with the fact that the animal is not 
accustomed to depend upon her own activity for the feed 
which she requires. 
An example of underfeeding accompanying a sudden 
change from dry feed to pasture is shown in Table VII. 
The data were taken at this Station. The animal used was a 
pure-bred Jersey weighing about 850 pounds. Her energy 
requirement for maintenance and milk production was about 
eight therms, which was just supplied by the dry ration. 
The animal was turned to pasture for the first time on the 
morning of May 20 and thereafter received no additional feed. 
The certainty that the animal would be underfed for a few 
