USEFULNESS IN ANIMALS 1 19 



repetition in breeding proper in character, the greater will 

 be the degree of the profit from keeping such animals for 

 breeding. The same is true of milk giving. There is 

 succession in its periods, and the longer the succession of 

 those periods, that is, the greater their number without 

 much diminution in the maximum of milk furnished by 

 each, the greater will be the return. With reference to 

 labor there is also succession, and more constant in char- 

 acter than is possible from either breeding or milk produc- 

 tion. It is in some instances daily repetition from year 

 to year. Its daily occurrence without the necessity for pe- 

 riods of temporary cessation other than those necessary for 

 rest from day to day, make its prolongation still more 

 important. The importance of such prolongation is fur- 

 ther emphasized by the fact that usually animals used for 

 labor, that is horses and mules, are not used for meat after 

 the labor term is ended. 



From what has been said, it will be very evident the 

 age limit of usefulness cannot be definitely fixed. With 

 animals grown primarily for meat, the shorter the life 

 period which duly considers the cost up to the time of birth, 

 and which does not involve too costly feeding, the better. 

 With animals maintained primarily for breeding and in a 

 secondary sense for meat production at the close of the 

 breeding period, the aim should be to prolong the period 

 of such breeding. The limit of such prolongation would 

 be the limit of capacity for breeding without any diminu- 

 tion in the individual prospective excellence in the progeny, 

 and without too much reducing the value of the carcass 

 when finally disposed of. With animals kept primarily 

 for milk production and in a still more secondary sense for 

 meat making, at the end of the milk-giving period, it is 

 still more important that the period of usefulness shall be 

 prolonged, since animals may be profitable for milk giving 

 for a longer period than it would be profitable to retain 

 progeny which they may bear for breeding uses. 



