194 THE CHEMISTRY OF CATTLE FEEDING 



These constituents are in all cases derived from the food, 

 i.e. from additional food over and above what is required for 

 maintenance. It is true that, in pregnancy, a foetus might 

 develop, and that a young animal might continue to giow 

 even under conditions bordering on starvation, but there 

 would be no increase in live weight. The foetus could only 

 develop at the expense of the pregnant animal, and a young 

 one which became enlarged would necessarily become 

 attenuated in corresponding degree. There can be no 

 increase of any kind unless the animal takes in more than 

 it gives out. It is obvious, therefore, that, in each case, the 

 animal must receive, at least, enough food to supply the con- 

 stituents deposited daily in addition to a sufficient maintenance 

 ration ; and it is desirable that such additional food should be 

 of a readily digestible kind. 



Pregnancy. The additions to be made to the maintenance 

 rations on account of pregnancy are so small, even in the case 

 of large animals like cows, as to be practically negligible. 

 The margin which should always be allowed over and above 

 the theoretical minimum requirements would generally be 

 more .than sufficient to provide for this trifling increase. The 

 question of pregnancy may, therefore, be dismissed without 

 further consideration. 



Growth. The additions required to provide for growth 

 are more considerable. Thus, in the case of calves growing, 

 not fattening, at an average rate of 2 Ibs. per day, the addition 

 should comprise at least 0*32 Ib. of protein and 0*95 Ib. 

 of starch or its equivalent in other nutrients. These are 

 minimum quantities, and various considerations render it 

 desirable that they should be increased. 



It is found, for example, that when calves are fed entirely 

 on milk, about 25 per cent, of the protein the whole of which 

 is digestible is excreted in the faeces. This nitrogenous 

 matter probably consists mainly of effete bowel membranes 

 and digestive enzymes. The amount of digestible protein 

 should, therefore, be not less than about 0*4 Ib. The non- 

 nitrogenous nutrients should also be increased to allow for 

 what is expended in the digestion of the food. The additional 



