12 



MASS. EXPERIMENT STATION BULLETIN 359 



the work progressed. In Table 8 the percentage of unsuccessful matings is 

 recorded by years for females of different ages, together with the mean fertility 

 of all birds except inbreds and outbreds each year. 



Table 8. — Progress in Improving Fertility 

 (Omitting Outbreds and Inbreds) 



The data show that fertility, as measured by the percentage of infertile matings, 

 did not change throughout the fifteen-year period. In other words, there was no 

 apparent tendency for the number of unsuccessful matings to decrease, but there 

 was a wide fluctuation from year to year. The last column of the table gives the 

 mean of individual fertility records by years and shows that there was no progress 

 in raising the mean level. These data lend no support to Jull's (1935) assumption 

 that fertilitv is an inherited trait. 



7. Relation Between Inbreeding and Outbreeding and Fertility 



Four types of matings have been considered in the inbred series: full brother 

 and sister, half-brother and sister, sire and daughter, and son and mother. Ex- 

 perimental evidence on the effects of inbreeding is not entirely conclusive at 

 present. 



Outbreeding, using outside stock within the breed, is believed by many to be 

 effective in increasing fertility. In these studies outside stock was used from five 

 different sources. Stock W was represented by 2 males, stock D by 14 males, 

 stock S by 4 males, and stocks T and P by males from hatching eggs obtained 

 from the two sources. Check matings include all matings in the flock not in- 

 cluded under inbreds or outbreds. 



Mean fertility may be taken as the average of the individual mating records of 

 each male when mated to one or more females. Fertility may also be measured 

 by the percentage of unsuccessful matings. In Table 9, the data for inbred, 

 outbred, and check matings are recorded in the two categories. 



