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 1 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 cerlainty that the animal would be underfed for a few 



