No. Gil] FERTILITY IN SOUTHDOWN SHEEP 667 



The figures for the per cent, of lambs per ewe and the 

 per cent, of twin-bearing ewes do not in all cases check 

 each other, as records of certain ewes were available for 

 the one column but not for the other. 



The writers tabulated birth frequencies in Shropshires, 

 Cotswolds and Dorsets with the following results : 



TABLE VI 



St?wold..'.'. '..'.'.'..'.'.:.. ^}>-i:l 1,4^1 20.53 m ^'.11 I ^ 



Dorsets seem to have an exceptionally high percentage 

 of triplets and quadruplets. 



Factors Affecting Fertility 

 Heape (5) in a study of 122,673 breeding ewes, 413 Eng- 

 lish flocks, suggests five physiological factors that may 

 affect the hereditary expression of fertility. The most 

 important factor according to him is the physical condi- 

 tion of the ewe, which must be vigorous and healthy, espe- 

 cially at tupping (mating) time. The second most 

 important factor is the feeding of the ewe, especially 

 flushing previous to breeding, and careful diet during 

 gestation. The third factor in importance is the district; 

 he cited the fact that the Suffolk in its native country pro- 

 duced 60.46 per cent, of twins, while in Essex it produced 

 only 42.87 per cent. The fourth factor in importance he 

 found to be the age of the ewe ; and the fifth, the season 

 of year at which mating occurred. 



Carlyle and McConnel (3) at Wisconsin discuss time of 

 mating and age of ewe, factors similar to those mentioned 

 by Heape. In a study of twelve years of records of the 

 station flock at the University of Wisconsin they found 

 that ewes bred early in the season dropped a higher per- 

 centage of lambs than those dropped late in the season, 



