Chapter V 



MISCELLANEOUS DEFECTS AND DISEASES 

 INTERFERING WITH FERTILITY 



There are many defects and diseases of other than the 

 genital organs which may render coitus physically difficult 

 or impossible, although the animal is fundamentally fertile. 



Much has been said of the physical difficulty of coitus be- 

 tween individuals representing extremes in size. This oc- 

 curs only when the disparity in size is so great that mating 

 is as a rule imprudent for other reasons. Extreme varia- 

 tion in size may render coitus difficult or dangerous. In 

 both horses and cattle it is not rare to observe successful 

 coitus of a large male with a female 30 to 40 per cent, of 

 his weight. The danger from such disparity is not great, 

 but when a stallion has an extra large penis this may have 

 great peril for the vagina of the mare. These injuries will 

 be discussed later. When a very small male attempts coitus 

 with a large female, failure is dependent ordinarily upon 

 the shortness of the hind legs of the male, making it impossi- 

 ble for him to reach the vulva. As a rule, however, the male 

 of a given breed of animals is able, not long after he reaches 

 puberty, to copulate with an adult female of his breed. In 

 horses and dogs, where giant and pigmy breeds have been 

 developed, coitus between these extremes is virtually im- 

 possible. The variations in weight between Clydesdale 

 horses and Shetland ponies, for instance, may be from 2400 

 to 200 pounds — or 12 to 1. In dogs the extremes reach 

 nearly 100 to 1. Disparity in size does not enter prominently 

 into the question of the physical possibility of copulating. 



A. Umbilic Hernia 



Umbilic hernia, especially in the bull, whenever of ma- 

 terial size, inhibits copulation by deflecting the penis as it 

 is being protruded. The defect is ordinarily not brought to 



