MEAT PRODUCTION 431 



608. Difference in feeding stuffs. The difference in the 

 character of the feed consumed by the animal at different ages 

 must not be overlooked. The very young animal subsists on 

 milk (or milk substitutes). As it grows older and begins to 

 consume solid feed, the latter must be at first of a rather con- 

 centrated character and highly digestible while, with advancing 

 maturity, the ration is likely to consist to an increasing extent 

 of coarser and more bulky materials. It is evident that to 

 make a direct comparison between animals receiving such dif- 

 ferent rations on the basis of the dry matter of the latter is to 

 ascribe to differences in the animals what is really due to differ- 

 ences in the feed. The ration of the younger animal will usually 

 have the higher percentage digestibility, while at the same 

 time it may cause a smaller expenditure of energy in the pro- 

 cesses of digestion and assimilation, so that the net energy values 

 of the rations per unit of dry matter are unequal. That an 

 animal shows a greater rate of gain on milk than later on a 

 mixed ration of grain and roughage does not necessarily show 

 that the younger animal made any more efficient use of the 

 materials actually resorbed, but may be simply because it re- 

 ceives more actual feed (net energy) in a unit of dry matter. 



509. Difference in composition of gain. It must also be 

 remembered that the cheaper gain made by the younger an- 

 imal means gain in live weight and that, as shown in Chapter 

 XI (458), this increase is of inferior food value as compared 

 with that of the more mature animal and represents the storage 

 of less energy, since it contains more water and a larger pro- 

 portion of protein to fat in its dry matter. A greater increase 

 in live weight, even on perfectly comparable rations, therefore 

 may be compensated for by the lower quality of that increase. 

 Gain by the younger animal is, so to speak, more dilute. 



510. Feed consumption. A third important factor, es- 

 pecially when the animal is not pushed to the limit of his capac- 

 ity, is the relatively greater consumption of feed by the younger 

 animal. While the individual consumes more feed per head as 

 it grows older, the consumption per unit of live weight and in 

 particular per unit of body surface decreases. For example, 

 in Henry's averages for swine and in Weiske's experiments on 

 growing lambs cited in Chapter XI (481 b, 487), the total feed 

 consumption was : 



