72 PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 



The high-protein calves in this experiment also gained at a subnormal 

 rate. The subnormal growth of the two Virginia steer calves, of two of 

 the Pennsylvania calves, and of the one Maryland calf is readily explain- 

 able on the basis of the low intake of protein, markedly lower than the 

 estimated requirements. The following seven calves made approximately 

 normal or supernormal gains in weight on amounts of protein but little 

 above the estimated requirements, in some cases in spite of an energy 

 intake much less than the intended: Massachusetts Nos. 18, 20, and 23,^ 

 Virginia ISTos. 3 and 4, Pennsylvania No. 974, and North Dakota No. 

 3A. It is true that Massachusetts calf No. 24 and Pennsylvania calf No. 

 1033 made subnormal gains on amounts of protein almost exactly equal 

 to the estimated requirements, but on the other hand, the Ohio calf grew 

 at a rate much faster than normal on an intake of digestible crude pro- 

 tein that must have been considerably less than the estimated require- 

 ments. No calf in the entire series of studies receiving more protein than 

 the estimated requirements grew at a subnormal rate. 



On an average of 18 digestion trials, the actual intake of digestible 

 crude protein by the low protein calves was found to be only 68 per cent 

 of that expected from average analyses and average coefficients of digesti- 

 bility, a fact readily explainable by the inclusion of large amounts of 

 starch in their rations.^ The starch thus added would increase the excre- 

 tion of metabolic nitrogen in the feces without increasing the nitrogen 

 intake. Hence, the estimated intakes of digestible crude protein in the 

 Ohio, North Dakota, South Dakota, Maryland, and Nebraska experiments 

 are probably much greater than the actual. 



From this study it seems fair to conclude that calves can grow at a 

 rate as great as that expected from available data on normal growth 

 with intakes of digestible crude protein but little if any greater than the 

 estimates developed in this report. In fact, with more liberal energy in- 

 takes, it may be possible that such growth could be attained upon even 

 smaller intakes of protein than these. 



A comparison of the tentative estimates of protein requirements in 

 Table 31 with the Missouri data on dairy calves. — Another extensive 

 investigation of the protein requirements of growing calves was conducted 

 at the Missouri Agricultural Experiment Station from 1913 to 1931 by 

 Swett, Eckles, and Ragsdale(^8). A total of 34 Holstein and Jersey 



* In the second Massachusetts experiment no consistent difference was noted 

 between the gains of the high-protein calves and those of the low-protein calves. 



^ The low-protein ration in the North Dakota experiments was not composited 

 according to the plan of these studies and contained no starch. Hence, the 

 estimated crude protein intake is not subject to this considerable error. 



