THE DEVELOPMENT OF ANIMALS 85 



of the former may be and usually is worth more two or three 

 years subsequently, and the same is true of milk production 

 in the latter. With the former, use has hardened the mus-. 

 cles so that they can endure more than when maturity was 

 attained, and habit in work has increased capacity for work. 

 With the latter, habit has increased capacity for milk giving 

 beyond what would have been possible when increase in 

 bodily development ceased. 



The period of highest usefulness, therefore, viewed 

 from the standpoint of production, including the results 

 from breeding, covers a period of years beginning with 

 maturity. With working horses this period may be said 

 in a general way to extend from the age of four to ten 

 years. With dairy cows it ranges from about the age of 

 three to eight years. With sheep, it extends from say two 

 to six years of age, and with brood sows from say one 

 to five years. This does not mean that animals should not 

 be retained beyond the ages named, but that the most profit- 

 able production is likely to occur between the ages named. 

 It will usually be profitable to keep good producing animals 

 longer than the period of highest production, especially 

 when they are reared on the farm, as an offset to the cost 

 of rearing up to the time when production began. It will 

 pay to keep some animals longer than others, because of 

 their relatively higher producing power. 



Much has been written, but not too much, as to the 

 unwisdom of breeding from animals at too early an age. 

 It is quite as important, nevertheless, that they shall not 

 be bred from at too advanced an age, for physical powers 

 considerably advanced in the decadent stage can no more 

 be expected to produce animals of highest excellence than 

 physical powers not yet perfected. While it is proper and 

 commendable to retain for breeding, animals of marked pre- 

 potency and high excellence as breeders for a longer period 

 than those of average merit as breeders, a time comes when 



