212 THE PRINCIPLES OF BREEDING 



absence of liA^e, vigorous spermatozoa. Sterility of the latter 

 class may be complete or only partial, as when the breeding 

 powers are impaired but not lost. Double cryptorchids, in which 

 both testicles are retained undeveloped in the abdomen, are usu- 

 ally sterile, while single cryptorchids (ridglings), in which one 

 testicle only is involved, may be sure breeders. The latter are 

 objectionable as sires, however, since the condition is frequently 

 transmitted, thereby seriously comjilicating the operation of 

 castration. 



Many instances are reported of imported stallions which have 

 had successful stud seasons abroad joroving impotent the first 

 year or two in this country, after which their potency is regained. 



Stallions remain jjotent to an old age as a rule. Many valu- 

 able sires are sacrificed just as their true worth is beginning to 

 be appreciated, because they are growing old. Experienced 

 breeders who retain their proven sires find them potent to an 

 advanced age and much more valuable than many untried young 

 stallions prove to be. Most stallions are sold with a guarantee 

 to get 60 per cent of brcedable mares in foal, but a much higher 

 percentage is maintained by some. 



Sterility or barrenness of the mare consists of an inability 

 to produce a li\dng colt. She may either be unable to conceive, 

 to carry the foal the full period of foetal development, or to de- 

 liver the foal alive at the conchision of gestation. 



Some mares are so irritable or excitable in the presence of 

 the stallion as to make it necessary to resort to artificial impreg- 

 nation in order to get them bred. 



If a twelve- or fourteen-year-old mare has never had a foal, 

 her generative organs have probably undergone more or less 

 atrophy from disuse, and the possibility of getting her with foal 

 is much lessened. There are numerous instances, however, of 

 quite old mares having become pregnant for the first time. Mares 

 frequently suffer from cysts or tumors of the ovaries, the irrita- 

 tion of which keeps them almost continually in heat and renders 

 them practically useless, yet they fail to get in foal, when bred. 

 Such mares should be spayed and considered as work geldings 

 rather than brood mares. 



