The Process of Breeding. 75 



mating also varies in animals, the average duration of 

 heat in the mare is two to three days, in the cow fifteen 

 to thirty hours, ewe two to three days, in the sow one to 

 three days. The presence of the male is often required 

 to prove the existence of the heat. If conception takes 

 place heat is not evinced again until after the birth of 

 the young. The cow will come in heat four weeks after 

 calving, the mare nine days after foaling; in ewes, except 

 Dorsets and their crosses, breeding wilk not be allowed 

 until fall, while sows show no signs of heat until after the 

 pigs are weaned, although conception has been known 

 to take place three days after farrowing. The time taken 

 by the ovum to reach the uterus may be two or three 

 days, in rare cases after becoming impregnated, the ovum 

 has fallen into the abdominal cavity and there developed. 

 Some animals are continually in heat; such is usually an 

 evidence of a diseased condition of the ovaries. Puberty 

 in the male is evidenced by the secretion of semen and 

 the presence of the sexual appetite. The contact of the 

 male organ, which must be erect, with the walls of the 

 vagina causes ejaculation of the semen. One single sper- 

 matozoon is sufficient to impregnate an ovum, such being 

 the case, numerous services during one heat should not 

 be permitted except in special cases. Impregnation is 

 as a rule only possible between animals of the same 

 species; hybrids are the result of crosses between differ- 

 ent species, such as between the donkey and horse, the 

 mule being the result. Hybrids will not breed. Artifi- 

 cial breeding by means of the capsule method is useful in 

 mares that are shy or difficult breeders, and in those who 

 throw out the semen. (See Sterility, p. 178.) 



