THE DEVELOPMENT OF ANIMALS 63 



and more especially the amount assimilated in the processes 

 of digestion. This is clearly evidenced in the fact that during 

 the finishing process two animals will consume practically 

 the same amount of food and yet one will make about twice 

 as much increase as the other. 



The foods fed usually change from the more to the 

 less concentrated forms, as with advancing age, the capac- 

 ity to dige,st more relative bulk continually increases. 

 These, as a rule, if not indeed always, have more of crude 

 fibre in them, hence the energy required to digest such 

 foods is more than is required to digest the former in pro- 

 portion to the nutriment obtained. More digestive energy 

 is used for instance in obtaining a given amount of nutri- 

 ment from timothy hay than in obtaining the same from 

 whole milk, and more energy is used in obtaining the 

 nutriment from ripe timothy hay than in obtaining it from 

 timothy cut at the blossoming stage. 



The food of maintenance gradually increases with ad- 

 vancing age. This arises first, from the increased demand 

 on nutrition to sustain the enlarging frame, to maintain 

 animal heat in the larger body surface exposed, and to 

 drive properly the machinery of digestion with the increase 

 in performance put upon it, and to repair the greater waste 

 of tissue relatively because of increase in the fleshy domain 

 where waste occurs. After the meridian of growth has 

 been attained, the decrease in the activity of assimilation 

 and the increase in the waste of tissue call for increasing 

 quantities of food to sustain the animal, hence so much less 

 is left for production. 



This law of development is fittingly illustrated in the 

 gains made by calves, lambs and foals at different stages 

 of growth. There is no real difficulty in securing two 

 pounds of gain daily during the first year of the life of a 

 calf, not including the weight at birth. It is more difficult 

 to secure an average daily gain in the same animal of 1^4 

 pounds the second year, and of 1^2 pounds the third year. 

 A lamb well nourished may be made to gain from say, 0.6 



