THE BREEDING SEASON 53 



with great irregularity. Failure to breed under these 

 conditions is not the result of a diseased condition of the 

 generative organs ; as Marshall has said, " It would seem 

 probable that failure to breed among animals in a strange 

 environment is due not, as has been suggested, to any 

 toxic influence on the organs of generation, but to the 

 same causes as those which restrict breeding in a state 

 of nature to certain particular seasons, in that the sexual 

 instinct can only be called into play in response to definite 

 stimuli, the existence of which depends to a large extent 

 upon appropriate seasonal and climatic changes." 1 



Among the domestic animals, the generative functions 

 are more active in the spring season. This is true of 

 the horse, the cow and the pig. Sheep breed more readily 

 in the autumn. 



How much the increased sexual activity of the domestic 

 animals may be due to climate and how much to the 

 change in the food supply, it is not easy to determine. 

 Food itself as distinct from climate has a direct influence 

 on the breeding powers of animals. The green succulent 

 grass upon which the animals feed in the spring may be 

 the efficient cause of increased sexual activity at that 

 season. The ewes that exhibit an increased tendency to 

 reproduction in the autumn may be stimulated in a similar 

 manner by the general abundance of fresh feed which is 

 characteristic of that season. It has long been the cus- 

 tom among skillful shepherds to provide fresh, succulent 

 feed in abundance to ewes at the time of turning in the 

 rams. This practice is called " flushing." The shepherds 

 claim that this practice causes the ewes to come in heat 

 more promptly and with greater regularity. It is also 

 claimed that a larger number of lambs will be produced 



1 Marshall, "The Physiology of Reproduction," p. 5. 



