INVESTIGATIONS ON TFIE METABOLISM OF MILCH COWS. 915 



tein and fat is supplied by the maternal organism in 284 days, or at 

 the rate of 35.2 gm. of protein and 5.3 gm. of fat per day. So far as is 

 known the unborn calf itself metabolizes materials, and can not utilize 

 tbe protein of the maternal organism directly. These materials 

 undergo a loss during metabolism. It may be assumed that the 

 maternal organism must supply about 20 per cent more protein and 10 

 per cent more fat than is actually required in order to make good this 

 deficiency. That is, 42.2 gin. of digestible protein and 5.8 gin. <>!' fat, 

 or an equivalent amount of carbohydrates, is necessary for the forma- 

 tion of the 35.2 gra. of protein and 5.2 gm. of fat mentioned above. 

 Although the fetus requires more material as it increases in size, the 

 average requirements for the fourth month are the quantities given. 

 The 12 kg. of milk produced would contain 480 gm. of protein, 420 gm. 

 of fat, and 000 gm. of milk sugar. Therefore the cow would require 

 480+42.2=522.2 gm. of protein for milk production and for the fetus, 

 in addition to a sufficient amount of other material, which maybe most 

 conveniently expressed in terms of energy. The fuel value per gram of 

 the protein under consideration is 5.711 calories; of the fat, 9.231 

 calories; and of the milk sugar, 3.052 calories. If a maintenance 

 ration consists of 8 kg. of meadow hay of good quality, the materials 

 added 10 make it a productive ration — for instance, peanut cake and fod- 

 der beets — must supply 522.7 gm. of digestible protein. Fodder beets 

 contain very little protein, and without introducing much error it may 

 be assumed that 50 per cent may be digested and assimilated. The 

 protein of peanut meal contains 18.2 per cent of nitrogen (instead of 

 the usual 16 per cent), therefore, 100 gm. of digestible nitrogen of pea- 

 nut meal could be stored in the body or used for milk production only 



in the proportion ( -^09 — =87.9 J. Seventy-three per cent of the 



nitrogen of peanut meal is digestible. Assuming that peanut meal 

 contains 7 per cent of albuminoid nitrogen, 100 gm. would supply the 



body with 28.1 gm. of available protein ( jg-^-X jq x 6.25 = 28.1 J. 



One hundred grams of fodder beets furnish 0.22 gm. of pure digestbile 

 protein. Assuming that X gm. beets and Y gm. peanut meal are fed, 

 the equation would be 281 Y+ 2.2 X = 522.2. The fuel value of the 

 total butter fat produced would be 3,877 calories (420x9.231 = 3,877). 

 The fat used for the formation of the fetus would be equivalent to 55 

 calories (5.8x9.5 = 55), and the milk sugar produced would be equiva- 

 lent to 2,371 calories (600 x 3.952 = 2,371). Therefore, in addition to the 

 protein mentioned above, the food must supply 3,877 + 55+2,371=6,303 

 calories. If this energy is supplied by fat and carbohydrates the 

 ration must also contain sufficient material to make up for the labor of 

 digestion and for the losses by fermentation. 



As previously mentioned, it maybe assumed that the energy supplied 

 by crude fiber is just sufficient for its mastication and digestion, while 



