^0. t t>Ei»AR*ME^fT OF AGRICULTURE. <M 



more economical to suffer some loss of digestibiHty than to pay 

 excessive prices for protein. Ordinarily, however, unless we go 

 to excess in reducing the protein of our rations to the lowest 

 possible limit, there need be little apprehension of loss on account 

 of impaired digestibility. 



The point of view having thus indicated, we come to the question 

 of the specific protein requirements, particularly of beef cattle. 

 This question we may sub-divide into three; first, as to the amount 

 of protein required by young, growing cattle; second, the amount of 

 protein needed for mature cattle; third, the amount required for 

 cattle at the age at which they are usually fattened in this country. 



First, young and growing cattle: Growth, of course, is the in- 

 crease of size of the body; that is to say, the body is increasing its 

 working machinery, therefore it calls for a liberal supply of protein, 

 because the working machinery is made up of protein. Consequently 

 the demands of young growing cattle for protein are larger than 

 those of maturer animals, and they have the capacity to store a 

 larger amount than the maturer animal. Of course, it is not fair 

 to compare the amount which a one hundred pound calf stores 

 with the amount which a thousand pound steer stores away, but 

 if we take a calf of about a week old, we find that it will store 

 in one day in its body protein amounting to about two and one- 

 third per cent of what it already has in its body. That is if there 

 were ten pounds in his body the calf will store up every day a 

 little less than a quarter of a pound. At that rate, it would double 

 its stock of protein in forty-two days. It might not exactly double 

 its weight, but it would double the weight of its working machinery. 

 When the calf is three weeks old it is able to add If per cent of its 

 protein stock in one day, which would be equivalent to doubling 

 its amount in fifty-eight days. At two months, it would require 

 about 150 days, to double the amount of protein in its body, storing 

 up a little over two-thirds or one per cent a day. A steer 2^ years 

 old would store only about 0.07 per cent, requiring, at this rate 740 

 days to double its stock of protein, while a week old calf would do it 

 in forty-two days. In other words, the capacity for storing protein 

 is highest in the young animal and decreases as the animal grows 

 older, and consequently the protein requirement of the young 

 animal is likewise high. 



If you have a young pig and you feed him largely on starchy 

 food, like cornmeal, the chances are that you will not give him 

 enough protein to supply the material for growth, and it will tend 

 to a production of fat, rather than meat. These are facts that are 

 fairly well known. The protein requirements of cattle, as in other 

 animals, are high in young animals and decrease as they grow older. 

 At the other extreme stands the mature fattening animal. Such an 

 animal needs sufficient protein to keep his bodily machinery in 

 repair, and probably very little, if any more. As I said before such 

 an animal needs something like half pound of protein for repair 

 material — certainly no more. Some experiments have indicated 

 as little as one-third of a pound, but half a pound is probably the 

 safer estimate — corresponding to a nutritive ratio of about one to 

 fifteen. The mature fattening animal is producing fat, and simply 

 keeping his bodily machinery in repair. He needs, therefore, chiefly 

 material to make fat, and very little protein. 



