378 NUTRITION OF FARM ANIMALS 



It is obvious that the error in single results obtained in this 

 way may be very considerable, but the general teaching of the 

 table is perfectly clear, viz., that the rate of growth of protein 

 tissue, like the increase in size or in weight, whether expressed 

 per unit of body protein or per 1000 live weight, is relatively 

 high in the new-born animal and decreases rapidly at first and 

 more slowly later, tending to be asymptotic to the zero line. 



Letting the g equal the gain of protein per day per 1000 live 

 weight and a the age in days, a curve represented by the em- 

 pirical equation 1 



corresponds fairly well with the general average of the observed 

 results on cattle and sheep. With swine, the few results ap- 

 pear to indicate a greater rate of growth during the first three 

 months. This is shown clearly in the accompanying graph 

 (Fig. 38) in which the individual results on the different species 

 are shown by the light lines, while the heavy curve is that repre- 

 sented by the foregoing equation. Of course considerable 

 individual variations are to be expected, and no particular 

 significance attaches to the mathematical form of the curve, but 

 it would seem that this formula may be used tentatively to 

 express in a broad general way the average rate of protein 

 growth of farm ruminants at different ages. The few results 

 on the dog and cat seem to indicate a higher rate of growth 

 in the young of these species. 



464. Rate of gain of energy. While the rate of increase 

 of protein, as discussed in the foregoing paragraphs, may be 

 regarded as the measure of growth in the more restricted sense, 

 and while it is of importance as an indication of the amount of 

 protein which must be supplied in the feed, the actual gain in 

 normal growth includes more or less production of fat, as is 

 clearly shown by the data regarding the composition of the in- 

 crease already considered (458). Growth, therefore, in practice 

 involves a storage of energy in the body not merely in the pro- 

 tein gained but also in the accompanying fat laid on, while it 

 is difficult to draw an exact line between the growth and the 

 fattening of young animals. 



1 The equation of a rectangular hyperbola. 



