694 NUTRITION OF FARM ANIMALS 



of different grades. As modified by his subsequent experiments, 

 this statement of requirements 1 has become known as the 

 Haecker standard, although, strictly speaking, it is not a 

 standard in the older sense. The writer 2 subsequently pub- 

 lished a tentative statement of the protein and energy require- 

 ments per pound of milk containing four per cent of fat and 

 illustrated the computation of rations on this basis, without, 

 however, attempting similar estimates for other grades of 

 milk. Later Woll and Humphrey, 3 Savage 4 and Eckles 5 

 have adopted various forms of the same conception. Henry 

 and Morrison 6 have included in their modified Wolff-Lehmann 

 standards Haecker's requirements for milk production and 

 also similar data, based on unpublished results by the same 

 experimenter, for growing fattening steers, and have also 

 widened somewhat the range of the standards for other pur- 

 poses and introduced minimum and maximum figures. 



On the other hand, however, all of the foregoing requirements 

 and standards, with the exception of Eckles', are expressed in 

 terms of digestible nutrients and are therefore open to the 

 criticism of ignoring differences in the relative values of nu- 

 trients from different sources. 



797. Requirements in terms of protein and energy. 

 The several chapters of Part III were devoted primarily to a 

 consideration of the feed requirements of farm animals in 

 terms of digestible protein and of net energy. In the case of 

 maintenance, these requirements may be regarded as to a cer- 

 tain degree fixed and capable of computation upon the basis 

 of the size of the animal, being related either to its weight or 

 to its body surface. In the case of productive feeding, on the 

 contrary, the obvious method of comparison is that of feed 

 (in excess of maintenance) with yield, and an attempt was 

 therefore made to estimate the feed requirements per unit of 

 product. The results of these estimates have been brought 

 together in Tables I- VI of the Appendix, which include also for 

 convenience estimates of the total requirements per day and 

 head for normal growth at different weights and ages. 



1 Minn. Expt. Sta., Bui. 140, p. 56. 



J U. S. Dept. Agr., Farmers' Bui. 346 (1909), pp. 19-25. 



3 Wis. Expt. Sta., Research Bui. 13. 4 N. Y. (Cornell) Expt. Sta., Bui. 323. 



6 Mo. Expt. Sta., Research Bui. 7. 6 Feeds and Feeding, isth Ed., p. 669. 



