8 PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 



to nitrogen equilibrium on a maintenance ration of 1 part of clover 

 hay to 5 parts of corn. During this period, the nitrogen output of these 

 steers averaged daily .046 gm. and .048 gm. per kilogram of weight, 

 equivalent to 0.29 and .30 part of protein per 1000 of weight. Titus (^°) 

 has determined the daily output of urinary nitrogen of three steers on 

 a ration containing 40 per cent of alfalfa hay and 60 per cent of paper 

 pulp. These values per kilogram of live weight are .042, .052, and .045 

 gm., or, in terms of protein per 1000 of weight, 0.26, 0.32 and 0.28. 



The Laboratory for Agricultural Eesearch in Copenhagen has pub- 

 lished (^i) the metabolism data from 2 dry cows subsisting upon a low- 

 nitrogen ration supplying 46 to 47 g-ms. daily. Nitrogen equilibrium was 

 established on this ration with average daily excretions in the urine of 

 14 gms. and 15 gms. of nitrogen, equivalent to .029 gm. and .034 gm. 

 per kilogram of body weight, or 0.18 and .21 part of protein per 1000 

 of body weight, 



Honcamp, Koudela, and Muller(^2) \^^yQ investigated the nitrogen 

 metabolism of 2 cows in milk on a low-nitrogen ration of oat straw, 

 corn, potato flakes, molasses, dried beet pulp, and salts. The nitrogen 

 intake was 85 and 89 gms. daily, and the urinary nitrogen output was 

 0.042 gm. and 0.035 gm. per kilogram of body weight, or .26 and .22 

 part of protein per 1000 of weight. If the disposal of endogenous metab- 

 olites is not influenced by the function of milk secretion, these values are 

 comparable to similar values secured on dry cows. 



The nitrogen output of 2 young growing heifers subsisting upon a low- 

 nitrogen ration was determined by Hart, Humphrey and Morrison (^^). 

 The calves weighed from 300 to 400 pounds and the ration used con- 

 sisted of wheat straw, corn starch, cane sugar, calcium phosphate and salt. 

 The average daily excretions of urinary nitrogen were equivalent to 

 0.036 gm, and 0,030 gm, per kilogram of weight, or 0,20 and 0,17 part 

 of protein per 1000 of weight. In a later somewhat similar experiment 

 upon a younger calf, Steenbock, Nelson and Hart(^*) obtained a mini- 

 mum excretion of urinary nitrogen of 0,045 gm, per kilogram of weight. 



The minimum excretion of urinary nitrogen per kilogram of body 

 weight, for various farm animals and man. — As Armsby's study of the 

 amounts of digestible feed protein per unit of body weight required for 

 the maintenance of weight or of nitrogen equilibrium has indicated a 

 remarkable similarity among different species of farm animals in this 

 respect, it is of interest to compare different animals also with respect to 

 the excretion of urinary nitrogen per unit of weight on nitrogen-free or 

 low-nitrogen rations. Such a comparison for the larger farm animals 

 from such available data as have been located has been made in Table 1. 

 The data in this table for each species are arranged in the order of 

 decreasing ratios of urinary nitrogen to body weight. 



