GENERAL CHEMISTRY OF MILK 123 



normal variation usually observed during the lactation period. 

 Such are the conclusions reached by Palmer and Eckles from a 

 recent study of this question. 



5. Influence of Food on Milk. — Authorities agree that the 

 food given to the cows has an intimate connection with milk 

 production, speaking both quantitatively and qualitatively. As 

 a rule producers have the firm conviction that they can increase 

 the yield of milk and fat by feeding certain foods rich in protein 

 and fat. Scientific investigations which have been carried on in 

 this country and abroad have not entirely confirmed this belief. 

 The use of drugs for increasing the yield of milk and butter-fat 

 has, according to McCandhsh, also proved futile. 



Studies on suitable rations for cows were commenced by Ger- 

 man investigators about the middle of the last century and stand- 

 ards for food balances proposed. A comprehensive literature has 

 accumulated since that time, and valuable contributions have 

 originated in Germany, Denmark, France, and from experiment 

 stations in this country. Prominent among these are the stations 

 of Vermont, Wisconsin, New York, IlUnois, Missouri, Minnesota, 

 Pennsylvania, Ohio, Connecticut, Utah, Kentucky, Michigan, 

 Massachusetts, Maine, Texas, and others. 



Although there are some points on which there is still some 

 difference of opinion, the main results of these studies are harmo- 

 nious. Contradictory results have been harmonized by perfecting 

 the nature of the experiments. Sometimes the period of observa- 

 tion has been too brief to warrant the conclusions drawn, as it is 

 known that sudden changes in food and of other factors, for that 

 matter, cause temporary changes in the quantity and quality of 

 the milk produced. These changes gradually disappear and opin- 

 ions based on short period observations have no lasting value. It 

 is now generally agreed that feeding experiments should cover 

 a sufficient length of time to get the animal accustomed to the 

 new rations, and several months are therefore required to get re- 

 sults. The longer the animals remain under observation, the more 

 valuable and trustworthy are the results. 



Like other animals, the cow requires protein, fat, and carbohy- 

 drate in suitable ratio and quantity. Food is utilized for three 

 purposes, namely: 1, for the growth of young animals; 2, for main- 

 tenance, that is to say, sufficient food of the right kind and quan- 

 tity to maintain weight without gain or loss, and 3, for milk pro- 

 duction. As a rule a good dairy cow is able to convert food in 

 excess of her maintenance requirement into milk. However, 

 when food is scant a cow will produce milk for aconsiderable length 

 of time by converting body substance into milk in order to care 

 for her young and preserve the species. Under such condi- 



