782 EXPERIMENT STATION RECORD. 



cerning the source of milk fat and other questions relating to the metabolism of the 

 milch cow are reported and briefly summarized as follows: 



"Three cows were used: Cow 12 fed a fat-poor ration in which the protein supply 

 was gradually decreased from 2.6 lbs. daily to 1.6 lbs. and then gradually restored to 

 the maximum, with accompanying increase and decrease in carbohydrates, so that the 

 digestible dry matter of the ration was kept fairly uniform; cow 10 fed a ration with 

 normal supply of fat at first which was gradually increased to 1.4 lbs. daily, then 

 gradually restored to the normal; and cow 2 fed the herd ration having a nutritive 

 ratio about 1:5.6. These rations were quite varied in character and contained some 

 fat-extracted foods, yet showed a quite miiform digestibility of about 70 per cent of 

 the dry matter. It is believed that this figure represents fairly the digestibility of 

 rations made up in part of silage and containing a fair proportion of high-class grains. 

 A widening of the nutritive ratios appeared to render rations less digestible, especially 

 the protein. The marked changes in protein content and in fat content of rations 

 did not produce noticeable changes in the character or composition of the ndlk. In 

 the former test, during 59 days, 18.4 lbs. of fat was formed in the milk which could 

 not have had its source in food fat or food protein and could hardly have been drawn 

 from the cow's body fat, as she increased in weight 33 lbs. in the same time. In this 

 test cow 12 in 74 days produced 39 lbs. of fat similarly unaccounted for, with a body 

 gain of 15 lbs. ; and cow 2, in 4 days, 1} lbs. These amounts of fat must have come 

 from the carbohydrates in the food. 



"A lessening of protein supply in the food did not ])roduce a corresponding decrease 

 in protein in the milk solids, but caused a marked lessenmg of protein decomposition 

 in the body. Calorimeter determinations show that the heat value of urine bears no 

 constant relation to its nitrogen content, and also prove that the formula used in 

 computing heat energy of urine, N X 5.343 cal., is greath' in error, actual results being 

 from 3 to 4 times as large as calculated by this formula. The energy values of nutri- 

 ents as given by Rubner — protein and carbohydrates each 4.1 cal. and fats 9.3 cal. — 

 appear to be fully high enough for herbivora, even when the loss due to escape of 

 unoxidized gases, methane chiefly, is not considered. 



"Over 40 per cent of the available energy value of the rations was used for main- 

 tenance, over 30 ])er cent reappeared in the milk solids, leaving a balance of from 

 one-fifth to one-fourth of the ration. The logical conclusion is that this balance, in 

 part at least, sustains the work of milk secretion." 



Fat in milk from starch in food, F. H. Hall et al. {Neiv Yoj-k State Sfa. Bui. 197, 

 popular ed., pp. 8). — A popular summary of the above bulletin. 



A feeding experiment ■with sheep, showing the influence of the fat in the 

 ration upon the amount and composition of the milk, A. Morgan et al. 

 {Chem. Ztg., 25 {1901), Nu. 87, pp. 951-95-i). — This experiment was carried on during 

 a portion of 2 years and was made with the object of ascertaining tlie influence of 

 the fat in food upon the fat content of the resulting milk. In comparison with the 

 usual ration, consisting of a number of common foods, rations were fed poor in fat 

 and ricli in fat. The ration poor in fat was made up of carboliydrates containing 

 small amounts of fat, and the ration rich in fat was made up in part of sesame cake 

 and peanut oil. The rations consisted of about 167 gm. of digestible protein and 600 

 gm. of nitrogen-free stuff including fat, to each 50 kg. of live weight. The fat con- 

 tent of the rations ranged about 10, 50, and 76 gm., respectively. The dry susbtance 

 of the milk obtained in feeding the ration poor in fat contained the following per 

 cents, more or less, than those obtained with the normal ration: Fat —7.1, sugar -f 2, 

 ash +0.5, and nitrogen +0.6 per cent. The ration rich in fat gave, in comparison 

 with the normal ration, the following per cents, plus or minus: Fat —1.2, sugar 

 +0.6, ash +0.1, nitrogen +0.05 per cent. These experiments will be continued, but 

 from the results so far obtained it would appear that fat in food in the form of sesame 



