No. 7. JjJiPAUTMKNT OF AGKICUL-TUKK. 195 



amount of waste product excreted in the urine. You cannot cause 

 the mature animal to build up tissue or lean meat in the body by 

 giving it more protein in the food. It will simply break down; all 

 the nitrogen will be disposed of in the urine of the animal. The best 

 you can do is to have this nitrogenous residue used just as you might 

 use starchy matter or fat; in other words, what practically happens 

 is, when you feed more protein to the mature animal than it needs, 

 you are simply using that protein for fuel, and you don't get any con- 

 structive work out of it. It simply serves either to run the animal 

 machine for the time being, or it may be stored up as food and used 

 in that way at some future time. In this respect, I am speaking of 

 the mature animal. 



In the case of a young animal, or a milking animal, we have a 

 somewhat different state of affairs. As I said, with the mature ani- 

 mal all the protein practically that is in the feed goes out in the 

 excreta, that is, if the protein breaks down. 



With the young animal, on the other hand, there is a possibility 

 of storing up extra protein; with a very young animal, there is a 

 very strong tendency that way. There were some experiments made 

 a number of years ago on a calf about a week old or so. That calf 

 ate^ in proportion to its weight, a large amount of protein in the milk 

 which was given to it and stored up about seventy' -five per cent, of 

 that protein, while if the same amount of protein had been given to a 

 mature animal, it would all have been broken down practically, that 

 is, the young, growing animal has a use for this extra protein in build- 

 ing up its tissues, consequently, it is safe to feed it more, because it 

 can store up this extra protein. As it grows older it gradually loses 

 that power; when it is a month old it stores up less protein; when it 

 is two months old, less still and so on. 



In the young animal, then, a certain excess of protein in the food 

 can be used. There is a place to put it. The same is true, to a de- 

 gree, in the animal that is producing milk. AVe all know that milk 

 itself contains in the neighborhood of three to three and a half per 

 cent, of protein, chiefly in the form of casein. In this respect, then, 

 the milking animal is somewhat like the young animal, that is, in 

 reference to using an excess or a larger amount of protein in its food 

 for constructive purposes than the mature animal not giving milk. 



We come now to something a little more definite, the bearing of 

 these general facts upon the subject of the necessary protein supply 

 of the dairy cow. How much protein does a dairy cow need? To 

 answer that question, let us consider, in the first place, what she 

 needs it for, in the light of what I have said. Like every 

 other animal, she needs a certain amount for maintenance, n 

 certain minimum amount to keep her vital machinery in repair and 

 make good the waste. That amount has been found to be in the 



