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SCIENCE PROGRESS 



grass, brewer's grains and undecorticated cotton cake are very similar, but the 

 productive index of average meadow hay and of oat straw is lower. 



Consideration of the starch equivalent per lb. of dry matter leads to much the 

 same conclusions, as may be seen from the following examples : 



These data serve to explain the well-known fact that roots may advantageously 

 form a large part of rations for production, whereas straw may not, though the 

 starch equivalent of the latter is double that of the former. Moreover, there is 

 reason to believe that animals consume more total dry matter when the rations 

 consist largely of roots. It is certain that the amount any given animal can con- 

 sume is limited. In a recent experiment the specific capacity for food of a fat ox 

 (1400 lb. live weight) was found to be 24*2 lb. of dry matter per 1000 lb. fat-free 

 live weight, but there is nothing to show whether it varies with the size, age, con- 

 dition, and the kind of animal. 



The basal katabolism of an ox of 1000 lb. live weight in store condition is 

 about 10*5 kt (4,900 CaL), and as the net energy of wheat straw is only o' 17 kt per 

 lb., about 62 lb. of that substance would be required for maintenance ; but if the 

 animal can consume only 25 or 26 lb. of the fodder, it must ultimately die of star- 

 vation. This result would accrue not, as has been said, because the animal 

 expends more energy on the food than it gets out of it, but simply because it can- 

 not eat enough to satisfy its requirements. Sawdust contains about 15 per cent, 

 of digestible organic matter, equal to about o'5 kt of metabolisable energy per lb. ; 

 but, as ingestion of the material increases metabolism by nearly twice that amount, 

 the nutritive effect is negative. In other words, sawdust does not retard, but 

 accelerates, the process of starvation. 



It is estimated that, if the basal katabolism of an ox were io'$kt in store 

 condition, it would be about 15 kt when the animal became fat. As pasture grass 

 contains about 22 per cent, of dry matter, 100 lb. per day would be about the limit 

 of the animal's capacity for this fodder. If the net energy of the grass were o' 1 5 kt 

 per lb., the animal might eventually attain the fat condition ; but if it were only 

 o'i2 kt, or less, as in some of the poorer pastures, the animal could not improve 

 beyond the half-fat condition, however large an area it was allowed to graze ; the 

 whole of the net energy of the largest amount of food the animal could consume 

 would be required for maintenance at that stage, and there would be no surplus 



