506 NUTRITION OF FARM ANIMALS 



thirty-one trials in which protein was substituted for carbo- 

 hydrates, twenty-six showed an increased yield of milk solids 

 and twenty-one an increased yield of milk fat. In thirteen out 

 of the entire fifty experiments, therefore, the presence of ad- 

 ditional protein failed to cause an increase in the milk solids, 

 while in twenty-three trials it failed to produce an increase of 

 milk fat. 



600. Effect of protein-rich feeds. In addition to investiga- 

 tions like those noted in the last paragraph, in which the effect 

 of an interchange of practically pure nutrients was studied, a 

 considerable number of experiments are on record in which an 

 enrichment of a ration in digestible protein has been effected 

 by an interchange of feeding stuffs, as for example, by the 

 substitution of cottonseed meal for maize meal. 



In all these experiments the low protein rations contained, 

 with one or two exceptions, a surplus of digestible protein above 

 the milk protein plus the estimated maintenance, yet a further 

 increase of digestible protein was followed by a larger yield 

 of milk per unit of organic matter digested, the increase rang- 

 ing from i per cent to 39 per cent. As in the experiments 

 described in the previous paragraph, the results appear some- 

 what capricious, showing no consistent relation between the 

 excess of protein supplied and the relative increase of milk pro- 

 duction secured. 



It should be added that in many of these experiments the 

 proteins of the low-protein rations consisted to a considerable 

 extent of maize protein, which has since been shown to be of 

 inferior nutritive value (783) . 



601. Protein fed in American practice. On the basis of 

 experiments and observations, Wolff l recommended a standard 

 for dairy feeding calling for 2.5 pounds of digestible protein 

 daily per 1000 pounds of live weight. Although later modified 

 by Lehmann, this standard was for many years almost uni- 

 versally accepted on Wolff's authority, supported by the un- 

 doubted fact that in many instances the addition of protein-rich 

 feeding stuffs to ordinary farm rations materially increased the 

 milk yield. Later observations, however, seem to indicate 

 that while protein is important the amount necessary in practice 

 has been somewhat overestimated. 



1 Die Ernahrung der landw. Nutzticre, 1876, p. 548. 



