STERILITY 117 



half and the number to one-fifth in the last or eleventh 

 service of the series as compared with the condition of 

 the semen at the first service." Other conditions which 

 are to be regarded as sources of barrenness are incomplete 

 erections, premature ejaculations, fear and repugnance. 

 The inability of the male to produce fertile semen may 

 be a congenital condition or it may be acquired through 

 some of the causes mentioned in this chapter. 



112. Sterility in the female. The failure of the 

 female to produce offspring is due to a variety of causes. 

 Some of these are inherent and cannot be successfully 

 treated. Such animals are permanently barren and of 

 course useless for breeding purposes. There are other 

 causes of infertility which are the result of purely tempo- 

 rary circumstances, and these may often yield to skillful 

 treatment by man and valuable animals thus become 

 regular breeders.. Some of the more important causes 

 of sterility which are temporary and which may yield 

 to treatment are mentioned below. 



113. Closure of the cervix. Mares and cows often 

 fail to become pregnant as a result of the constriction of 

 the muscles forming the neck of the womb. This spas- 

 modic closure of the cervix prevents the passage of the 

 semen from the vagina into the uterus, and the fertiliza- 

 tion of the egg is thus prevented. This condition is more 

 frequent in young females that have never been pregnant, 

 but is not uncommon among animals that have previously 

 given birth to offspring. This condition may generally 

 .be successfully treated by a simple operation known to 

 the stallioners as opening. The treatment for this con- 

 dition is admirably and clearly described by Law 1 as 

 follows : " Spasmodic closure of the neck of the womb 



1 " Diseases of the Horse," U. S. Department of Agriculture, 1907. 



