MILK PRODUCTION 171 



protein may be formed from the non-protein nitrogenous com- 

 pounds (amides) and the non-nitrogenous nutrients together. 

 This, however, could occur only when there is a deficiency of 

 protein and a considerable excess of non-nitrogenous nutrients, 

 together with the necessary amides, in the food. Under 

 ordinary circumstances, we may take it that the nitrogenous 

 matter of the milk is derived entirely from the true protein of 

 the food. The question remains what quantity of this nutrient 

 is required. 



It was shown (p. 133) that for animals of 1000 Ibs. live 

 weight the maintenance ration must supply a minimum of 

 about | Ib. of digestible protein per day, and that on other 

 grounds it is generally desirable to allow more. In the case 

 of cows in milk it has been found that when the rations 

 contain a sufficient amount of digestible non-nitrogenous 

 nutrients, the whole of the excess of protein, beyond what is 

 actually required for maintenance, can be used for milk pro- 

 duction. For example, if the maintenance ration contain 

 i Ib. of digestible protein, and a certain quantity of digestible 

 fat and carbohydrates is added to it, the extra J Ib. of protein 

 will not be oxidised, but will appear in the milk. If each 

 pound of milk contains 0*035 Ib. (3*5 per cent.) of protein, 

 the extra \ Ib. would be sufficient for about 14 Ibs. of milk. 

 Theoretically, then, the rations for milk cows should contain 

 at least 0-035 Ib- of digestible protein, in addition to the 

 quantity (J Ib.) required for maintenance, for each pound of 

 milk produced. 



Pat. Any excess of protein, beyond what is required for 

 maintenance and what appears as such in the milk, undergoes 

 chemical change. The nitrogenous part is split off and 

 discharged in the urine, but the remainder or some of it 

 is converted into milk fat (p. 113). It will presently be 

 shown that milk fat can be produced at less cost from other 

 constituents of the food, but a certain excess of protein is 

 nevertheless desirable; it appears to stimulate the mammary 

 glands and increase the secretion of milk. Perhaps it would 

 be more correct to say that unless a certain excess of protein 

 (beyond what is required for maintenance, and what appears 



