DAIRY FARMING — DAIRYING. 697 



Such a ration, extremely poor in fat but which was found adapted to the experi- 

 mental animals, inasmuch as they not only remained in good condition hut gained 

 in live weight, was not favorable to milk production. The substitution of a thermi- 

 cally equivalent quantity of fat for a portion of the carbohydrates in such a ration 

 exerted a very favorable influence upon milk production, increasing the yield of 

 milk and milk constituents and also the percentages of fat and milk solids. 



The substitution of protein for a like quantity of carbohydrates in the ration defi- 

 cient in fat was also favorable as regards milk production, but was without influence 

 on the fat content of the milk, and therefore not able in this respect to take the 

 place of food fat. In rations deficient in fat neither carbohydrates nor protein could, 

 therefore, be substituted satisfactorily for food fat furnished in quantities of 0.5 to 1 

 gm. per kilogram of live weight. 



Increasing the food fat to 1.5 to 2 gm. per kilogram live weight caused, in individual 

 cases only, a further increase in the production of milk fat, while in other instances 

 the increase was without influence or the larger quantity was even of less value than 

 the smaller quantity. It is, therefore, concluded that from 0.5 to 1 gm. of fat in food 

 per kilogram of live weight is apparently sufficient in general for the function which 

 food fat exerts in milk production. 



The experiments are belie veil to furnish additional proof to the generally accepted 

 view that food fat is by no means the only constituent that enters into the formation 

 of milk fat. The addition of either peanut oil or mutton tallow to the ration defi- 

 cient in fat increased the iodin and refractometer numbers of the milk fat to normal 

 figures or at times above. The two fats had practically the same effect in this 

 respect. 



Food from which the fat had been extracted, but to which fat was later added in 

 the forms mentioned, did not exert the same influence on milk production as a normal 

 ration showing the same composition, which difference in influence is attributed to 

 a loss of certain irritating or stimulating substances in the former case. In some of 

 the experiments this deficiency was very nearly overcome by the addition of irritat- 

 ing substances, such as fennel, anise, or hay extract. The influence of irritating 

 substances in the absence of food fat was less marked and uncertain. Such sub- 

 stances so far as studied had no influence upon the properties of the milk fat. 



As regards live weight of the animals, the different rations showed only a small 

 but varying influence, yet taking the results as a whole, it is considered clear that 

 the food deficient in fat exerted not only no unfavorable influence, but rather a 

 favorable one on live weight, which, in view also of the fact that the animals were 

 always in good health, showed that such food is very satisfactory for maintenance. 



The principal results of the investigations may therefore be stated as follows: To 

 a certain extent food fat exerts an invariably favorable influence on the production 

 of milk fat, and in this influence fat can not be replaced by carbohydrates or pro- 

 teids. Moreover, food fat appears to be a specially favorable material for the forma- 

 tion of milk fat. In the food of dairy animals fat can not therefore be omitted, 

 while for the maintenance of animals it may be a more nonessential food constituent. 



From the standpoint of practical feeding, the experiments, so far as they go, show 

 that in all normal rations fat is entirely sufficient for milk production, and that an 

 addition of fat and materials rich in fat is necessary only when the rations are com- 

 posed of Btraw, roots, or other materials very poor in fat. The manner in which 

 food fat exerts its influence is discussed, the conclusion being drawn that like other 

 food constituents it serves merely as material for the formation of milk, but is for 

 this purpose an exceptionally suitable material, perhaps better than protein, at any 

 rate better than carbohydrates. 



In these experiments irritating substances, such as fennel, anise, and malt sprouts, 

 were believed to have exerted no favorable influence upon digestion and a favorable 

 influence directly upon the cells concerned in milk secretion only in cases where 



