PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 41 



Furthermore, " in almost any selection of adipose tissue a few nuclei may 

 be seen crowded in the angles between the fat cells. The protoplasm 

 around these nuclei is so small in amount that it can hardly be dem- 

 onstrated. From a study of fattening animals I am convinced that these 

 interstitial cells may form many new fat cells when the animal fattens. 

 It is generally believed that a cell does not divide after any considerable 

 amount of fat has been deposited in it." Further studies of these inter- 

 stitial granules of muscle and their relation to the nutrition of the ani- 

 mal were reported by Bell in later papers (*^). 



Atmshy's prediction equation of the rate of gain of protein at different 

 ages. — In 1908 Armsby(*''^) computed the daily gains in protein of 

 calves, lambs, and a number of pigs of varying ages from available slaugh- 

 ter data, and observed that when these gains were expressed per 1000 

 pounds live weiglit they exhibited similar variation with age, expressible 

 by the very simple hyperbolic equation 



in which g is the gain of protein per day per 1000 pounds live weight 

 and a is the age of the animal in days. A general similarity among dif- 

 ferent species of animals in the rate of gain of protein during growth 

 would be remarkable, and it becomes a matter of great interest to com- 

 pare the gains in nitrogen of the Missouri steers in Groups I and II at 

 different ages with the prediction obtained from Armsby's equation. 

 Such a comparison, at the ages at which the body weights are 300, 400, 

 etc., pounds, is afforded by the computations contained in Table 32. 



The Armsby equation gives a very poor prediction of the nitrogen 

 gains by the Group I steers, greatly underestimating the early gains, and, 

 to an even greater extent, over-estimating the later gains. Probably the 

 Armsby equation will not apply to animals carrying as much fat as the 

 steers of this group. 



For the steers of Group II, a much better fit was secured between the 

 rates of nitrogen retention computed from the Missouri data and the 

 rates predicted by the Armsby equation for animals of their weight and 

 age, though the agreement is not particularly good. Again the Armsby 

 equation underestimates the early gains in spite of the fact that the 

 equation used above to describe the relation between age and nitrogen 

 content (13), from which the rate of nitrogen retention has been com- 

 puted, underestimated the nitrogen content of the steers less than 6 

 months of age (see Table 10). Also, with Group II, as with Group I, the 

 later daily gains of nitrogen are greatly over-estimated by the Armsby 

 equation, which would lead one to expect a much more protracted gain 



