A STUDY OF NITROGEN METABOLISM 

 IN THE DAIRY COW. 



By CHARLES CliOWTHEH. .\1.A., rii.JJ. 

 AND HERBERT ERNEST WOODMAN, D.Sc, Pii.l). 



The work outlined in the present communication icas carried out during 

 the years 1916-19 in the Institute for Research in Animal Nutrition of the 



University of Leeds. 



In an earlier conunuiiicatioii' dealing with the results of a series of 

 digestibility determinations carried out by us with two sheep, attention 

 was directed to the fact that, w^hen the averages for consumption and 

 excretion of nitrogen in the different periods were arranged in the order 

 of increasing nitrogen consumption, the retention of nitrogen in the body 

 of the sheep rose only up to a certain point and then fell. The essential 

 data are reproduced below: 



Period Nature of ration 



1 Hay I palm kernel oake I 



IV Hay alone 



II Hay + palm kernel cakes I and 1 1 



V Hay + extracted palm k. meal ... 



Ill Hay + undec. cotton cake 



VI Hay + dried yeast 



It will be noted that each sheep showed the maximuni retention of 

 nitrogen in Period II, in which about 12 gni. digestible nitrogen, or 

 roughly 17 gm. total nitrogen (= 106 gm. total crude protein) per head 

 per day (= 2-4 kg. total crude protein per 1000 kg. live-weight) were 

 consumed. In the periods following this in the table, as the nitrogen- 

 consumption increases the nitrogen-retention falls steadily. 



These results suggest that, judged by nitrogen-retention, there is an 

 optimum point of protein supply, above or below which nitrogen-reten- 

 tion is reduced. It was realised, however, that this series of observations 

 could not be regarded as in any way conclusive on this point, in view of 

 ' Journ. ofAgric. Sci. 8 (1917), 447. 



