THE INFLUENCE OF FEED ON MILK SECRETION 199 



1. The Influence of Feed on Milk Secretion 



When fresh cows are underfed it may be observed that more nutri- 

 ents are excreted with the milk than are supplied in the feed, or, in other 

 words, that a part of the milk is formed from the tissues of the body and 

 that the latter is gradually losing weight. A certain degree of emaciation 

 is frequently observed in fresh cows. The question whether, as a result 

 of intensive breeding, the cow's udder has been developed to such an 

 extent that the digestive organs are unable to keep pace with it, may be 

 an open one. However, milk secretion can not be continued indefinitely 

 at the expense of body tissues and is bound to suffer sooner or later both 

 as to quantity and quality (Kuehn). If the food supply is relatively de- 

 ficient in phosphate of lime the phosphorus content of the milk may be 

 reduced to tlie extent of 30 per cent (Weiskes). Weiskes was unable to 

 discover an analogous deficiency of lime. 



A decrease in the milk yield occurring in the course of lactation as a 

 result of deficient food supply may to some extent be corrected by lib- 

 eral feeding, and both solids and fat content, the latter in particular, can 

 be increased. Concomitant with this there is an improvement in the 

 animal's general condition. The influence of nutrition or food, on the 

 milk yield, as already emphasized, is confined within certain limits. A 

 number of factors that influence milk yield, Uke individuality, breed, 

 natural lactation period, etc., can not possibly be overcome by feeding. 

 Within certain limits, however, in which the food supply affects the milk 

 yield, there seems to exist a zone in which the yield is in proportion to 

 the food supply. Beyond this zone every increase in milk yield requires 

 greater amounts of food until a stage is reached where increases are no 

 longer profitable. 



The proteins, of all the nutrients, have the greatest influence upon 

 milk secretion. This is especially true as to quantity. The quality on 

 chemical composition is less affected by the proteids. On the other hand, 

 the effect of the nonalbuminous nitrogenous compounds like asparagin, 

 ammonium acetate, etc., is not very marked. 



The effect of the nitrogen-free nutrients on milk secretion is subject 

 to the influence of the proteids. When feed that is rich in albumen but 

 deficient in nitrogen-free nutrients is given, the milk yield suffers and, 

 vice versa, if nitrogen-free nutrients are added, the yield is increased, 

 especially quantitatively. On tlie other hand, if the feed administered 

 has been deficient in proteids and the discrepancy is widened by the fur- 

 ther addition of carbonaceous nutrients, the result may be a depression 

 of the digestive functions and a further decrease of the milk yield. This 

 may not occur if the rations are somewhat less deficient in proteids. As 

 a matter of fact, if the animals in question are otherwise good producers 

 but in a poor or run-down condition, the addition of carbohydrates may 

 result in an actual increase of yield, due to the improved physical con- 

 dition of the animal. Thus it may not seem strange that numerous ex- 



