PRINCIPLES OF flORSE BREEDING 259 



tend to produce it in the individual are worthy note. 

 While many of the factors that influence prepotency are 

 little understood, those that do aid and are under the con- 

 trol of man are : First, purity of breeding, which makes 

 for stability. The introduction of outside blood lessens 

 the stability and the certainty of transmission. Second, 

 strong constitutional development, which strengthens the 

 characters; and, third, in-breeding, which aids pre- 

 potency, as it strengthens dominant characters. 



In breeding horses the prepotency of the male is given 

 more consideration than the female. This is due to the 

 fact that the sire is the parent of more individuals than 

 the dam, and not to individual resemblance. This is 

 fortunate, as improvement can be more cheaply secured 

 through a good sire from the mere fact that he is repre- 

 sented in more progeny. 



Fertility. — The number of offspring produced by horses 

 • of either sex varies greatly. Some mares fail to breed at 

 all, some breed once and go barren, and some breed every 

 other year; while others breed with much regularity. 

 The English Thorovighbred mare Pocahontas produced 

 fifteen living foals and lived to the age of 33 years, while 

 Old Fanny Cook also produced fifteen, the last one in the 

 twenty-ninth year of her life. Stallions vary likewise, 

 some producing a very low percentage, while others are 

 almost fully fertile. The Standardbred stallion, Gam- 

 betta Wilkes, has 229 standard performers, and Allerton 

 has 246, while there are 10 that have over 150 (p. 120). 

 In these cases, however, much depended upon the oppor- 

 tunity, as the better the sire the better the class of dams 

 offered, and hence the better the offspring, all of which 

 leads to still further opportunities. 



Sterility. — Perhaps the horse breeder's greatest diffi- 

 culty is the failure of his animals to breed freely. The 

 causes which lead to sterility are many, some of which 

 are understood and more or less preventable, while others 

 are little known and perhaps beyond control. Some of 



