PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 77 



In attempting to reconcile these two views, Harding in his recent 

 article on metabolism in pregnancy (^^) believes that the former applies 

 to the lower animals and the latter only to the human organisms. How- 

 ever, it appears that much more investigational work should be done be- 

 fore this compromise position can be considered with complacence. 



Apparently the only evidence of this nature bearing on bovine preg- 

 nancy has been contributed by Crowther and Woodman (^2), who deter- 

 mined the nitrogen balance of a pregnant cow (D) and of a dry cow not 

 in calf (C) over long periods of time. The data bearing on the question 

 at issue may be briefly referred to. Cow D was bred on September 6, 

 after which the collection of excreta was unfortunately suspended until 

 November 8. On resumption of the metabolism experiment, the cow 

 was found to be in slight negative nitrogen balance which persisted for 

 three weeks, at which time a positive balance was established and main- 

 tained until parturition. Before being bred, Cow D had shown through- 

 out a uniformly higher positive nitrogen balance than Cow C, but when 

 the experiment was thus resumed, the reverse relation was observed. The 

 authors, therefore, conclude that the cow, like the dog and the rabbit, 

 suffers a disturbance in its nitrogen metabolism in the first stage of 

 pregnancy, and this conclusion is accepted by Harding in the review of 

 the subject previously cited. 



However, another conclusion from this extensive study is that " even 

 after nitrogen equilibrium is established and a relatively constant nitro- 

 gen consumption is maintained, there may arise from time to time con- 

 siderable deviations from equilibrium either in the positive or negative 

 direction. It would appear therefore that for reliable work of this char- 

 acter long experimental periods are essential." Such an apparently 

 fortuitous disturbance in the nitrogen equilibrium of Cow C occurred 

 about December 1 and a considerable negative nitrogen balance persisted 

 for five weeks on an intake previously adequate for nitrogen storage. The 

 point may therefore be raised that the similar disturbance of Cow D, to 

 which such great import is attached, may be of this fortuitous nature and 

 thus may bear no relation to conception or pregnancy. 



The investigations thus briefly reviewed evidently have an important 

 bearing upon the problem of the protein requirement for pregnancy in 

 cattle, since if the condition of pregnancy disturbs the nitrogen economy 

 of the maternal organism, either by inducing excessive tissue catabolisra 

 or a storage of nitrogen greatly in excess of the needs of the fetus, the 

 rate of nitrogen retention by the fetus and its membranes would not 

 represent the total nitrogen requirements of pregnancy, but would be 

 something less than these. The subject is of great physiological interest 

 as well as of practical importance. 



