478 NUTRITION OF FARM ANIMALS 



A combination of the two systems may also be used, one 

 group of animals being fed varying rations in successive periods, 

 while the other receives a uniform ration throughout the entire 

 experiment. 



A very complete discussion of the methods of eliminating the in- 

 fluence of advancing lactation in the interpretation of the results of 

 experiments on milk production is to be found in a recent article by 

 Morgen. 1 



3. THE INFLUENCE OF ENVIRONMENT ON MILK PRODUC- 

 TION 



The word environment is here used loosely as a convenient 

 term to summarize all those external influences other than feed 

 which may affect milk production. The dairy cow appears 

 to be particularly sensitive to external conditions, some of the 

 more important of which are considered in the following para- 

 graphs. 



Milking 



Milking is but an imperfect imitation of the suckling of the 

 young, and naturally its efficiency in securing the milk is likely 

 to be affected by a variety of circumstances. 



573. Frequency of milking. As already stated, the cavities 

 of the udder in heavy milkers cannot hold all the milk produced 

 at one milking. Between milkings there evidently may be a 

 considerable accumulation of matter in the alveoli and canals 

 which appears to have the effect of diminishing the secreting 

 activity of the epithelial cells through what might be crudely 

 called " back pressure." Suckling or milking would have the 

 effect of relieving this " pressure " and perhaps rendering 

 secretion more easy, while at the same time it seems to act as a 

 direct stimulus to secretion. At any rate it is a fact that more 

 frequent milking tends to increase the yield of milk, especially 

 in the case of good cows and in the earlier stages of lactation. 

 The effect of frequent milking is strikingly illustrated in the 

 following experiments by Kaull. 2 The abrupt falling off in the 

 milk yield when the milking was made very frequent may per- 



1 Landw. Vers. Stat., 77 (1912), 351. 



2 Cited by Kellner, Die Ernahrung der landw. Nutztiere, 6th Ed., p. 521. 



