FERTILITY 599 



of the process being to get the animals in an improving condition 

 without permitting them to put on too much fat. If the 

 artificial feeding is excessive and the sheep are forced to depend 

 for the remainder of the year upon a mere sustenance diet, it is 

 easy to understand that they would tend to deteriorate, and 

 their subsequent fertihty become impaired, owing probably to 

 a higher frequency of follicular degeneration. It is seemingly 

 for such a reason that some flockmasters regard the practice of 

 flushing as one altogether to be deprecated. There is some 

 evidence, however, that if sheep are specially fed in one season, 

 the process must be repeated in the next, and that if this is 

 omitted the sheep tend to be less fertile than if they had never 

 been subjected to flushing. 



It has already been mentioned (p. 335) that the practice of 

 flushing tends to hasten the sexual season, the sheep coming 

 " on heat " sooner than they would otherwise. The result 

 must be ascribed to a general increase in the ovarian meta- 

 boHsm consequent upon the stimulating power of the special 

 food supply. Conversely, it has been shown that in ewes which 

 are poorly fed the sexual season is often retarded, and the 

 fertihty of the flock reduced. So also the occurrence of a snow- 

 storm, or other unfavourable climatic condition, occurring during 

 tupping time will cause a corresponding scarcity of twin births 

 in the following lambing season. There can be Httle doubt, 

 therefore, that the conditions which exist during tupping time 

 are largely responsible for controlling the fertihty of the flock, 

 and that favourable conditions tend to promote the more rapid 

 growth and maturation of the foUicles in the ovary, and cause a 

 greater number to discharge their ova during the cestrous periods. 



It would appear also that the condition of the ewe is a far 

 more important factor in determining the number of twin births 

 than that of the ram ; but it is obvious that the number of ewes 

 which one ram can serve successfully must depend upon the 

 degree of vigour possessed by the latter. Sixty ewes to one 

 ram is about the usual proportion allowed.^ 



• It is said that a good stallion should be able to serve eighty mares in 

 one season, and get on an average forty to fifty foals. See Wallace, loc. cil. 

 The reproductive capacity of the male animal is almost invariably far 

 greater than that of the female. 



