FEEDING STANDARDS CALCULATING RATIONS 135 



purposes, on the basis of their net energy content, is theoretically more 

 accurate than the Wolff-Lehmann method of comparing them in terms 

 of the digestible nutrients they furnish. Unfortunately, the net-energy 

 values have actually been determined for but a few feeds, and with 

 these only for the fattening ox. For other feeds and other classes of 

 animals, the values which may be computed are but approximations. 

 On the other hand, during the last half-century scores of thousands 

 of analyses of feeding stuffs have been made, as shown in Appendix 

 Table I, and large numbers of digestion experiments have been con- 

 ducted in which the coefficients of digestibility have been determined, 

 as given in Appendix Table II. Thus the values for digestible nutrients 

 in the various feeding-stuffs, given in Table III, rest on a reasonably 

 secure basis, tho we must remember that different kinds of animals 

 digest somewhat different percentages of feeds, especially of roughages. 

 (85) 



The value of a concentrate and of a roughage for productive purposes 

 can not be compared on the basis of the digestible nutrients each fur- 

 nishes, for in the roughage., containing more fiber, a larger part of the 

 energy in the digested nutrients is used up in the non-productive work 

 of mastication, digestion, and assimilation. (78-80) In the ordinary 

 rations for each class of animals, concentrates and roughages are, how- 

 ever, usually fed in about the same proportions. This tends to lessen 

 any error due to inaccuracy in computing rations according to the 

 Wolff-Lehmann method. Furthermore, the prescription of a definite 

 allowance of dry matter is a check upon the net-energy value of the 

 ration. If a ration contains sufficient digestible nutrients to meet the 

 Wolff-Lehmann standards, but carries an excess of dry matter, obviously 

 too much roughage or concentrates too high in fiber have been used 

 and the net-energy value will consequently be too low. On the other 

 hand, if the content of digestible nutrients satisfies the standard, while 

 the ration does not contain the dry matter called for, it indicates that 

 feeds more concentrated in character than necessary have been used, in 

 which case some roughage or feeds higher in fiber may be substituted till 

 the dry-matter content is brought up to the standard. With this simple 

 check any large error in f ormulating the ration may be avoided. 



188. Necessity for modifying the Wolff-Lehmann standards. -It has 

 already been shown in this chapter that in several instances the original 

 Wolff-Lehmann standards do not set forth the actual requirements of 

 farm animals as revealed by the many experiments which have been 

 carried on since these standards were drawn up. We know, for example, 

 that the allowance of digestible crude protein prescribed is higher than 

 is needed by fattening animals, dairy cows, and work horses. Yet 

 these standards were more commonly employed in this country, 

 except perhaps with the dairy cow, than any other system for formu- 

 lating rations. Indeed, the authors have found feeders, annually 

 fattening hundreds and even thousands of animals, who were balancing 



