286 FEEDS AND FEEDING 



or third hour even more protein will have been digested than had the 

 horse remained at rest. Contrary to some statements, exercise does not 

 hasten the passage of food from the stomach into the small intestine, 

 but apparently retards it. Severe labor may, however, depress digestion. 

 Grandeau and LeClerc found that hard work at a trot lowered the di- 

 gestibility of the protein 7 per ct. and of the fiber 13 per ct., compared 

 with the amounts digested when the horse was allowed to rest after eat- 

 ing. The greater depression observed in the case of the crude fiber is 

 doubtless due to the fact that this nutrient is digested mainly in the 

 caecum and large intestine and is hurried thru these organs by the motion 

 of the horse in action. 



447. True value of feeds for work. As previously shown (78-80), the 

 true value of different feeds for work is not based merely on the amount 

 of digestible nutrients they contain, for a varying percentage of the 

 available energy in the digestible portion of the feed is used up in the 

 work of mastication and digestion, and thereby lost so far as useful me- 

 chanical work is concerned. By subtracting the energy thus used from 

 the available energy which the digestible nutrients of any feed furnish, 

 we will find the amount of net nutrients which may be used in the per- 

 formance of such external work as propelling the body, carrying a burden, 

 or pulling a load. We should remember, however, that the energy 

 which is used up in mastication and digestion is all changed into heat, 

 and so may aid in keeping the body warm. 



It has been pointed out in a previous chapter that the net energy val- 

 ues for various classes of animals differ to a greater or less extent and 

 that in most of the experiments carried on to determine the net energy 

 value of feeds, fattening steers have been used. (177) Armsby 8 has 

 recently computed the net energy values for a few feeds when fed to the 

 horse, using the results of Zuntz and Hagemann 9 and the analyses and 

 the digestion coefficients given in Appendix Tables I and II of this book. 

 These are given in the table on the next page. 



It will be noted that these net energy values differ quite widely from 

 those for ruminants. (171) For example, the net energy value of dent 

 corn for ruminants is given as 89.16 therms and for horses, 112.80 therms 

 per 100 Ibs. The net energy value of alfalfa hay for ruminants is reported 

 as considerably lower than that of timothy hay. On the other hand, in 

 this table the net energy value of alfalfa hay for horses is given as nearly 

 double that of timothy hay. These values should be regarded as merely 

 approximations, showing the relative value of typical feeds for the pro- 

 duction of work. The table shows a negative net energy value for wheat 

 straw of 20.90 therms per 100 Ibs. This means that the work of masticat- 

 ing, digesting, and assimilating wheat straw uses up more energy than 

 the straw furnishes. This feed therefore is worse than worthless for 

 feeding a hard- worked horse. However, straw is of value for maintaining 



s Nutrition of Farm Animals, 1917, p. 721. 

 'Landw. Jahrb., 27, 1898, Sup. Ill, p. 431. 



