502 NUTRITION OF FARM ANIMALS 



which can possibly meet the requirements of the milk-producing 

 animal is the quantity required for the maintenance of the body 

 protein plus the actual amount of protein contained in the milk 

 yielded. For example, if a looo-pound cow is to produce daily 

 25 pounds of milk containing 3.2 per cent of total protein, 

 it is evident that her ration must contain in digestible form 

 at least the 0.8 pound of protein contained in the milk plus 

 the approximate 0.6 pound presumably required for body 

 maintenance, or a total of approximately 1.4 pounds. A less 

 supply than this must evidently result either in a falling 

 off in the milk yield or in a conversion of body protein into 

 milk protein. 



How much more than this minimum amount must be sup- 

 plied by an adequate ration will depend upon the percentage 

 utilization of the feed protein in the sense already discussed in 

 4 of this chapter (584-586), i.e., upon the proportion of it 

 capable of conversion into milk protein. Thus in the illustra- 

 tion just employed, if 80 per cent of the surplus feed protein 

 can be utilized the protein requirement would be i .o pound for 

 milk production plus 0.6 pound for maintenance, or 1.6 pound 

 instead of 1.4 pound. The case is parallel with that of the 

 protein requirement for growth discussed in Chapter XI (484- 

 491) and in both instances the experimental data available are 

 insufficient for a final conclusion, although the probabilities 

 appear to indicate the possibility of a high percentage utilization 

 under favorable conditions. 



599. Protein as a stimulus to the milk glands. The fore- 

 going considerations do not, however, exhaust the subject. In 

 them it has been tacitly assumed that the amount of milk protein 

 manufactured by the milk glands is substantially fixed. It 

 seems well established, however, that in addition to furnishing 

 material for the manufacture of milk protein, the nitrogenous 

 matter of the feed may act to some extent as a stimulus to the 

 glands, causing a more active secretion not only of protein but 

 of all the milk solids. In other words, it would appear that a 

 greater or less surplus of protein over the amount indicated by 

 calculations like the foregoing is necessary if it is desired to take 

 full advantage of the milk-producing capacity of the animal or 

 to delay as much as possible the natural shrinkage in milk due 

 to advancing lactation. 



