510 NUTRITION OF FARM ANIMALS 



The results for the entire year and likewise for the winter rations 

 showed on the whole a somewhat greater and a decidedly more 

 economical average production on the smaller supply of pro- 

 tein. The protein content of the milk is not stated, but esti- 

 mating it at 3.38 per cent and allowing 0.6 pound per 1000 for 

 protein maintenance, the approximate surplus of thfe available 

 protein (digestible protein minus maintenance requirement) 

 over the milk production in the winter rations was as shown 

 in Table 143 in each of the nine years. 



603. Summary. In view of the great differences between 

 individual cows both as to yield and composition of milk, it is 

 clear that no one figure can express the protein requirement for 

 milk production per day and head, but that it must vary with 

 the amount and character of the milk produced. 



It appears to be fairly well established (586) that the digesti- 

 ble feed protein of ordinary mixed rations may be converted 

 into milk protein without any very great loss and that conse- 

 quently a moderate rate of milk production may be maintained, 

 at least for a time, on rations furnishing a comparatively small 

 surplus of digestible protein over the milk protein plus the 

 requirement for maintenance. 



On the other hand, however (599, 600), both experiments with 

 pure proteins and those in which an increase in the protein con- 

 tent of rations has been secured by the use of protein-rich feeds 

 seem to indicate clearly a stimulating influence of excess protein 

 on milk production, although in the majority of cases the effect 

 was not very large. Contrary to what might have been antici- 

 pated, however, an increase in the digestible protein of the ration 

 appears to have been on the whole quite as effective with ani- 

 mals already on a high plane of protein nutrition, i.e., receiving 

 a large surplus over the minimum requirement as with those 

 on a much lower level of protein supply. This appears 

 with especial clearness in Morgen's experiments on sheep. 

 The results therefore fail to indicate the limits within which 

 this stimulating effect is manifest or to establish any quantitative 

 relation between the surplus protein supplied and the additional 

 milk yielded. They afford no basis, therefore, for any estimate 

 of the extent to which a stimulation of milk production by means 

 of excess protein will be economically profitable under any given 

 conditions. 



