448 NUTRITION OF FARM ANIMALS 



supply more digestible protein than is called for by the estimates 

 in Appendix Table IV b. When protein feeds are especially ex- 

 pensive an even smaller proportion of protein might doubtless 

 be used to economic advantage, even though at the expense of 

 some loss of digestibility, without unduly curtailing the pro- 

 tein supply, especially in the case of animals approaching 

 maturity. 



527. Specific effects of feeding stuffs. Account must be 

 taken also of the fact that in most of the experiments upon the 

 protein requirement thus far reported the variation in the 

 protein supply was effected by varying the proportions of cer- 

 tain concentrates in the ration, such, e.g., as substituting cotton- 

 seed meal for maize. As was suggested in Chapter XI (491), 

 however, such a substitution may not only affect the ash bal- 

 ance of the ration but may serve to introduce substances which 

 stimulate the growth process or perhaps the fattening process. 

 While we are not to suppose that such substances can take 

 the place of actual nutrients (738), they might enable the 

 protein in the ration to be more fully utilized, or they might, 

 by stimulating the fattening process, create an appetite for more 

 feed. 



At any rate it seems to be the general experience of stockmen 

 that the addition of certain feeds rich in protein, especially the 

 oil meals, to the rations of fattening animals tends to induce 

 them to consume feed more freely and thus (518) to yield more 

 profitable gains. 



Energy requirements for meat production 



528. Combined growth and fattening. An attempt was 

 made in Chapter XI (480-483) to estimate approximately the 

 net energy values required at different ages for normal growth 

 without material fattening. To the extent to which the fatten- 

 ing process is to be carried on at the same time, these require- 

 ments must evidently be increased by amounts equal to the 

 additional net energy stored up in the increase of adipose tis- 

 sue desired or expected. Subject to the limitations indicated 

 in previous paragraphs, this additional energy may be supplied 

 by the addition of either nitrogenous or non-nitrogenous ma- 

 terials to the growth ration. 



