FERTILITY 619 



heavy continuous rains, as well as to the feeding of the ewes 

 on unripe watery roots and unwholesome, filth-laden shells. 

 Heape has suggested that abortion on the Wolds arises partly 

 from the practice of unduly crowding the ewes on turnip fields. 

 As already mentioned, a bacillus has been isolated from outbreaks 

 of abortion in ewes, and has been used to infect other ewes for 

 experimental purposes in the laboratory. 



The Increase of Fertility, a Problem of Practical 

 Breeding 



Heape ^ has shown from statistical evidence that the amount 

 of money invested in Uve stock in this country cannot be com- 

 puted at very much less than £450,000,000, and this sum does 

 not include the enormous capital spent on buildings, land, 

 vehicles, and various accessories. The annual export of hve 

 stock from Great Britain in recent years has been tending 

 steadily to increase, until it has reached a total value of £1,750,000. 

 It is clear, therefore, that in this country the breeding industry 

 occupies a position of no inconsiderable importance, and that the 

 scientific study of the problems of breeding possesses a great 

 national interest. Foremost among these problems is that 

 which concerns itself with the factors that control fertility. 



Despite its comparative prosperity, it is evident that the 

 breeding industry suffers annually from no inappreciable loss. 

 Allusion has been made to the losses sustained by breeders 

 owing to the occurrence of abortion in domestic animals. 

 Sterility, whether persistent or temporary, is responsible for a 

 greater reduction of profit. The prevalent barrenness among 

 the better class of Shire mares has been already referred to, 

 while incapacity to breed is perhaps still commoner among 

 thoroughbreds. As already mentioned, the Royal Commission on 

 Horse-Breeding found that no less than forty per cent, of the 

 mares chosen for breeding in any given year failed to produce 

 offspring.^ Moreover, there is evidence that in certain districts 



^ Heape, The Breeding Industry, Cambridge, 1906. 



^ Owing probably to a combination of circumstances, the number of foals 

 dropped in this country in recent years has shown a tendency to decrease. 

 This fact has called forth serious comment in many quarters, and attention 



