INHERITANCE OF FERTILITY IN SOUTHDOWN 

 SHEEPi 



EDWARD N. WENTWORTH 

 Professor op Animal Breeding 



J. B. SWEET 



Assistant in Experimental Breeding, University op Wisconsin 

 Intkoduction 



YOUATT (14)2 says: 



The disposition to twinning is undoubtedly hereditary: 

 " Ewes yearly by lambing rich masters do make : 

 The lambs of such twinners for breeders go take." 



Flockmasters of the last century have made selections 

 on this assumption, while the increased number at a 

 birth in the progeny of ewes born multiparously as com- 

 pared to the progeny of those born singly has been dem- 

 onstrated by several investigators. In general there has 

 been shown to be an increase in number produced at a 

 birth as the average birth values of the animals lambing 

 increase. Thus, Rietz and Roberts (13) present the fol- 

 lowing in Shropshires, the number at a birth being repre- 

 sented by the figures 1, 2, or 3 : 



1 I 1.3452±0.0059 3,059 



1 1.3946±0.0073 2,088 



2 j 1.4171 ±0.0067 2,436 



- 2 1 1.4o48±0.0088 1,5^0 



_0 II e parent a triplet 1.6076 ±0.030 158 



Experimental investigations of the inheritance of twin- 

 ning in sheep have been attempted in few cases. Ains- 



