450 NUTRITION OF FARM ANIMALS 



be stimulated to the greatest extent possible. In fact, how- 

 ever, other considerations come in to modify this conclusion. 



531. Influence on digestibility. Overfeeding to the ex- 

 tent of causing digestive disturbances and throwing the animal 

 " off feed " is of course to be avoided, since the resulting dis- 

 turbance and the subsequent lessened consumption of feed 

 may outweigh any advantage from the increased amount eaten. 

 It is the regular uniform feeder that is likely to be the profitable 

 animal rather than the one with a capricious appetite. 



But aside from this danger, it seems well established that 

 the percentage digestibility of mixed rations, such as would be 

 used in productive feeding, decreases more or less as the quantity 

 consumed increases. The results on record in this respect (722) 

 are scarcely sufficient for any quantitative estimate of the mag- 

 nitude of this effect, but it is evident that it must tend to di- 

 minish the efficiency of the rations. 



532. Influence on net energy values. Such a decrease of 

 digestibility as that just noted is, of course, equivalent to a 

 decrease in the net energy value of the rations. There appears 

 to be a somewhat general impression, however, that in addition 

 to this effect on digestibility, the matter and energy actually 

 resorbed from the ration become less efficient in producing 

 gain as the amount of the ration is increased in other words 

 that when the organism is flooded with the resorbed products 

 of digestion, the katabolic processes are stimulated and a larger 

 share of the energy of the digested matter escapes as heat. 

 As appears in Chapter XVII (764), the evidence on this point 

 as yet seems hardly sufficient to warrant positive statements. 

 The net energy values of feeding stuffs which have thus far been 

 reported have been obtained chiefly in experiments on rations 

 ranging from submaintenance to only moderately heavy fatten- 

 ing rations, and the results show no distinct indication of a 

 decrease with increasing amounts of feed. On the other hand, 

 physiological considerations render it quite conceivable that 

 the effect of the feed in stimulating metabolism and so increasing 

 the heat production (365) may be relatively greater on a high 

 than on a low nutritive plane. 



Apparently more or less falling off in the nutritive effect of 

 a fattening ration as its amount is increased must be antici- 

 pated, whether on account of decreasing digestibility or of 



