19161 DATET FARMING DAIRYING. 775 



result of overfeeding was to cause the cow to gain in weight, and that in 

 none of the experiments did overfeeding exert an influence toward abnormality 

 in composition of the milk or milk fat. In one case a high supernormal plane 

 of nutrition prevented further changes in the constants of the milk fat due 

 to declining lactation. In two cases where the composition of milk and the 

 constants of the fat were abnormal, due to previous underfeeding, the result 

 of overfeeding was to restore normality. The conclusion is reached "that 

 normal milk and butter is to be expected when the cow is on a supernormal 

 plane of nutrition as well as when the plane of nutrition Is normal, provided 

 there are no other influencing factors such as specific feeds." 



Data obtained on the effect of overfeeding on milk flow indicate that the 

 secretion of milk is regulated by at least two factors, designated as chemical 

 and nervous. Facts brought out in the investigations are thought to show 

 that the chemical stimulus, which is the stimulus that fixes the maximum milk 

 flow and which is more or less independent of the plane of nutrition, is the pre- 

 dominating stimulus immediately following and for a period after parturition, 

 but that as the lactation period advances the chemical stimulus gives way 

 for the nervous stimulus. The nervous stimulus is dependent upon the plane 

 of nutrition of the cow. 



In one case only was there a marked increase in milk flow due to a super- 

 plane of nutrition. In this case th'^ milk flow of the cow had been appreciably 

 reduced by underfeeding. The results indicate, however, that a very high 

 plane of nutrition is effective in holding off the decline in milk flow due to 

 advanced lactation. 



In two of the four experiments the percentage of fat was slightly affected 

 by overfeeding. In one case there was a reduction of 0.2 per cent, but this 

 accompanied an increased milk flow, the total fat production remaining practi- 

 cally constant. In the other case a high fat content due to previous under- 

 feeding was restored to normal. With three of the cows the protein content 

 of the milk, which in each case had been appreciably depressed, was restored 

 to normality by overfeeding. In the other case intense overfeeding caused a 

 constant high protein level of from 0.4 to 0.5 per cent throughout the entire 

 period. This fell back to normal when the plane of nutrition was reduced. 

 This increased protein percentage was accompanied by an increased milk flow. 



The lactose percentage was the least uniformly affected by supernormal feed- 

 ing. In the case of the Jersey cow, which started her lactation period in a 

 very low state of nutrition and with an abnormally low lactose percentage 

 in the milk, the lactose content was gradually raised to its normal value. 

 The only effect of overfeeding on the saponification value of the milk fat 

 was a strong tendency to produce r normal value. This was also true of the 

 Reichert-Meissl number, the oleic acid content, and the melting point of the 

 milk fat. 



The influence of the state of nutrition on the composition of milk fat im- 

 n-.ediately following parturition is discussed. 



Data connected with the experiments are tabulated in detail and shown 

 graphically in the appendix. 



The changes in composition of butter fat produced by feeding cotton-seed 

 oil, F. H. Smith, C. A. Wells, and P. V. Ewing (Georgia Sta. Bui. 122 (1916), 

 pp. 95-111). — This is a detailed report of investigations previously noted 

 (E. S. R., 35, p. 71) on the changes in composition wiiich milk fat undergoes 

 when the animal receives a ration containing cotton-seed oil, and on the trans- 

 fer of food fat to the milk fat. 



