PRODUCTION OF WORK MILK, AND WOOL 103 



upon here lead scientists to believe that the chemical changes by which 

 energy is liberated are not simple oxidations, but are more in the nature 

 of sudden decompositions or cleavages of some complex substance or 

 substances built up in the muscle during rest, carbon dioxid being 

 evolved in such cleavage. Part of the energy liberated in this decom- 

 position appears as heat, and another part as mechanical work. 4 



Glycogen, or animal starch, is stored in the muscle during rest, forming 

 between 0.5 and 0.9 per ct. of the weight of well-nourished muscle in 

 the resting condition. (60) A smaller quantity of glucose is also found 

 in the muscular tissues. During muscular activity this stored glycogen 

 and glucose disappear, in proportion to the extent and duration of 

 the contractions, so that after prolonged muscular activity or hard 

 work the supply may be entirely exhausted. Tho the amount of these 

 carbohydrates in the body tissues at any one time is small, a supply, 

 especially of glucose, is being continuously produced from the food 

 nutrients or body tissues to replace that oxidized in the production 

 of work. As the larger part of the food of farm animals consists of car- 

 bohydrates, the oxidation of the glucose formed from them probably 

 furnishes most of the energy for the production of heat and work by 

 these animals. To supply the muscles with the necessary oxygen and also 

 carry away the waste products formed during muscular exertion, the 

 circulation of the blood must be hastened and larger quantities of air 

 be taken in by the lungs. 



141. Food requirements for work animals. We have seen in the pre- 

 ceding paragraphs that theoretically an animal needs no more protein in 

 its feed when at work than when idle, since the energy used in the pro- 

 duction of work is normally furnished by the carbohydrates of the ration 

 or by the fat in some instances. Protein is used up in work only when the 

 ration contains insufficient of these other nutrients. In trials mentioned 

 later (454), work horses have been successfully fed rations in which the 

 nutritive ratio was as wide as 1 :21 to 1 :28. However, as has been 

 pointed out previously (84), when the nutritive ratio is wider than 1:8 

 or 1 :10, the digestibility of a ration is usually decreased, causing a waste 

 of feed. Also, it is believed that a supply of protein somewhat above the 

 minimum requirements tends to give work animals better life and spirit. 

 Accordingly, in the Morrison feeding standards, nutritive ratios not 

 wider than 1 :7.0 to 1 :8.5 are recommended, a somewhat narrower nutri- 

 tive ratio being advised for hard work than for light work. (Appendix 

 Table V.) The mature animal when at work has need for but little 

 more mineral matter than an idle one which is merely being maintained. 

 Therefore, all ordinary rations will furnish an ample supply of the 

 various mineral nutrients, except common salt. Immature work animals, 

 which have not yet reached full size, will need a somewhat more liberal 

 supply of protein and mineral matter than mature ones. 



From the foregoing, it is evident that the primary need in rations 



4 Armsby, Nutrition of Farm Animals, pp. 533-4. 



