670 EXPERIMENT STATION BECORD. [Vol.36 



to a subnormal plane of nutrition immediately after parturition maintain their 

 milk flow at u nearly constant level under the most adverse conditions. In one 

 experiment a constant flow was maintained for 30 days with sufiicient food 

 for body maintenance only. A decline in milk flow accompanies even moderate 

 underfeeding when the lactation period has reached a certain stage. The exact 

 point when this occurs was not determined in the experiments. The explana- 

 tion of this difference in the elfect on the milk flow is believed by the authors 

 to rest on the conception that the milk flow of the cow is stimulated by two 

 factors, (1) chemical, (2) nervous. The former is more or less independent 

 of the food supply and predominates for a period of time after parturition. 

 The latter is almost entirely dependent on the food supply and predominates, 

 or replaces the chemical stimulus, after the lactation period has attained a 

 certain stage. 



" Physiological underfeeding and reduction in the plane of nutrition from a 

 high to a normal plane is invariably accompanied by a marked increase in the 

 percentage of fat in the milk, especially when the cow has a surplus store of 

 fat on her body. In the case of physiological underfeeding there is almost 

 invariably an actual increase in the yield of milk fat, as well as in the per- 

 centage in the milk [E. S. K., 27, p. 280]. The efi'ects of an induced subnormal 

 plane of nutrition on the percentage and yield of fat in the milk are variable, 

 an increased fat percentage sometimes resulting, in other cases there being 

 no change, while in others an actual decrease in the percentage of fat results. 

 The factors that appear to cause these variations are the state of flesh of 

 the animal, the degree of underfeeding, and the season of the year in which 

 the experiment is conducted. 



"A subnormal plane of nutrition at times affects the percentage of protein 

 in the milk. In some of the experiments conducted there was a decline in 

 the percentage of casein, while in others the total protein only was affected. 

 In the latter cases the percentage of ash in the milk also decreased. None 

 of the types of underfeeding influenced the percentage of lactose in the milk. 



"All types of underfeeding have marked effects on the physical and chemical 

 constants of the butter fat, which are characterized by a decline in the 

 Reichert-Meissl number and saponification value and an increase in the iodin 

 value. Three types of results were noted with respect to the effects on the 

 melting point of the butter fat, (1) increase in melting point, (2) stationary 

 melting point, and (3) decrease in melting point. These differences are ex- 

 plained by the facts that in the group of experiments with increased melting 

 point the decline in the volatile fatty acids was relatively greater than the 

 increase in the oleic acid. In the group of experiments with constant melting 

 point, the changes in the two kinds of fat constituents offset each other with 

 respect to their effects on the melting point. In the group in which the melt- 

 ing point declined, the increase in oleic acid was relatively much greater than 

 the decline of the volatile fatty acids. 



"The proportion of volatile fatty acids in butter fat has a much greater 

 influence on the melting point than the proportion of oleic acid. This was 

 strikingly shown in several of the underfeeding experiments, in which marked 

 changes in the melting point of the fat occurred with variations in the Reichert- 

 Meissl number in spite of the fact that the iodin value remained abnormally 

 high throughout the experiment. 



" The more important factors influencing the effects of underfeeding on the 

 fat constants are the character of the ration, the degree of underfeeding, and 

 the length of the underfeeding period. Corn silage and other feeds which in- 

 crease the volatile fatty acid content of butter fat, affect the degree of abnor- 

 mality of the fat constants accompanying underfeeding, but not their amount of 



