52 A Studji of Nitrogen Metabolism in tin' Ihih-ij Cmr 



This figure represents a iiiiniimiiu estimate, since it does not include 

 the nitrogen of the fluids, wliich were collected with the urine and not 

 analysed separately. Thus, whereas 1050 gni. nitrogen had been stored 

 as tissue in the form of calf and placenta. Cow D had been able, on a 

 ration only very slightly heavier than that which served for its protein 

 requirements when not in calf, to obtain 773 gm. from its food for this 

 purpose. The deficit of 277 gm. must have been supplied from the 

 maternal protein at the average rate of about 1 gm. per day. 



A cow in calf is thus able to maintain a positive nitrogen-balance on 

 a ration differing only slightly from that requisite for nitrogenous equi- 

 librium in the ante-pregnant period, though under such circumstances, 

 it may have to supply from its own protein a fraction of the nitrogen 

 necessary for foetal growth, and thus be unable to build up the desirable 

 reserves during pregnancy to enable it to come into lactation with a 

 good milk flow ca])able of being sustained over a long period. More 

 generous feeding than was given in this investigation is obviously 

 necessary in actual farm practice, especially in view of the heavy negative 

 nitrogen-balances shown by Cow D in the days following parturition. 



For the first three days after calving it was thought inadvisable to 

 increase the ration, but on the fourth day (day 590) the allowance of 

 linseed cake was raised to 8 lb. This immediately checked the loss of 

 nitrogen from the body, but as the cow at this stage could barely con- 

 sume the ration, the allowance of linseed cake was reduced two days 

 later (day 592) to 6 lb., whereupon a marked nitrogen deficit was again 

 established. On day 595 the allowance of linseed cake was again raised 

 to 8 lb. and nitrogen-equilibrium was practically restored, this changing 

 to nitrogen-retention when on day G08 a further 1 lb. of cake was given 

 {vide Table VI). 



For the period covered by Table V Cow C, dry and not in calf, was 

 again in nitrogen deficit (see below) following a short period of nitrogen 

 storage from day 502 to 575. 



N consumed N voided Mean daily Change in 

 (average (average nitrogpn- weight for 

 Daily ration (days 580-603) per day) per day) balance period 



gm. gm. gm. lb. 



215 lb. hay + 1 lb. linseed cake 143-8 ISoO - U-8 +2i 



Comments on Table VI (Fourth Main Period of E.xperiment). 



It will be noted from Tables V and VI that a positive nitrogen- 

 balance was not estabUshed in Cow D until three weeks after parturition. 

 It was then consuming daily aiiout .3.30 gm. nitrogen and was yielding 

 about 27 lb. of milk, containing roughly GO gm. N per day. That the 



