48 FEEDS AND FEEDING, ABRIDGED 



the proteins and carbohydrates contained therein from the action of 

 the digestive juices. This depression does not occur when nitrog- 

 enous feeds, such as oil meal, are added along with the starch or 

 sugar, thus preserving the balance between protein and non- 

 nitrogenous nutrients. It is assumed that this is due to a stimula- 

 tion of the bacteria by the addition of more protein, so that, invig- 

 orated, they attack the fiber of the food again. 



Adding nitrogenous feeds to roughages, such as hay, straw, etc., does 

 not increase the digestibility of the roughage. Neither does the addi- 

 tion of fat to a ration increase the digestibility of the other con- 

 stituents. When too much fat is fed it may cause digestive disturb- 

 ance. Salt does not affect digestion, tho it may cause animals to 

 eat more food and may improve nutrition. 



Class of animal, age, breed, and miscellaneous factors. — Cattle 

 and sheep digest concentrates and good quality roughage equally 

 well, but cattle digest poor roughage, such as straw, somewhat better 

 than sheep. Horses and pigs digest fiber less completely than do rumi- 

 nants. While there is little difference in the digestibility of con- 

 centrates by these animals, horses cannot digest roughages as com- 

 pletely as do cattle or sheep, and pigs utilize roughages still less 

 effteiently. 



In general, age does not, in itself, influence digestibility, tho young 

 farm animals cannot utilize much roughage until their digestive tracts 

 are developed. The digestion of old animals is often indirectly 

 injured by poor teeth, which make the proper mastication of their 

 food impossible. Breed has no influence upon digestibility. Animals 

 may, however, show considerable difference, one from another, in 

 their ability to digest the same ration, tho ordinarily the digesti])ility 

 of a given ration by different animals of the same race will not vary 

 more than 3 to 4 per ct. 



Neither the frequency of feeding, the time of watering, nor the 

 amount of water drunk appears to influence digestibility. Moderate 

 exercise tends to increase digestibility, but excessive work lowers it. 



The flow of saliva and the other digestive juices is checked by fright. 

 On the other hand, kind treatment and palatability of food should 

 favorably influence digestion. Under skillful care animals show 

 remarkable relish for their food, and it is reasonable to conclude that 

 better digestion results. 



Summary. — The preceding discussions make it evident that average 

 figures for the composition of any feeding stuff are but approximately 

 correct when applied to a particular lot of the feed. This likewise 

 applies to the expression of its nutritive value, whether stated in terms 

 of digestible nutrients or net energy. In other words, different lots 



