No. 611] FERTILITY IN SOUTHDOWN SHEEP 



673 



Table XII shows the relative breeding performance of 

 the sires and dams in pedigrees started from twin births. 



Treating the sires in pedigrees from twin births as in 

 Table X, Table XIII is produced. 



TABLE XIII 



L.5296 ± .00543 

 1.5682 db .00724 

 1.6154 =fc .06435 



The dilference between singles and twins as sires is 

 .0386 + .0091; between singles and triplets is .0858 

 + .0645 ; and between twins and triplets is .0472 + .0647. 



The difference between singles and twins is in this case 

 significant, being about 4.2 times the probable error. 

 Further consideration will be given this difference when 

 the ewes are discussed. 



Treating the ewes in pedigrees from twin births as in 

 Table XI, Table XIV is produced. 



0.51075 

 0.51583 

 0.41811 



The difference between singles and triplets is 0.2513 

 + .05098; between twins and triplets, 0.2191 + .05132 ; 

 and between singles and twins is 0.0322 + .01011. Ewes 

 from triplet births give significantly larger progenies 

 than ewes from single or twin births, while ewes from 

 twin births give significantly larger progenies than ewes 

 from single births, the last difference being 3.323 times 

 the probable error. It is interesting to observe that both 



