POULTRY FLOCK IMPROVEMENT 7 



highly satisfactory. However, the records show a steady advance in body and 

 egg weights. With the exception of lower production in the second hybrid gen- 

 eration, which was influenced very greatly by unfavorable weather conditions 

 during the fall and winter of 1933-34, fecundity was very satisfactory. 



Hatchability 



Experimentation has shown that hybridizing with strains as well as with breeds 

 gives a decided improvement in hatchability. But in order to show definitely the 

 difference in hatchability between the flock sisters of the males used and the 

 foundation or hybrid flocks each year, a number of flock sisters were placed 

 with the hybrid females so that they would be served by the same males. It was 

 necessary to trapnest the females during the breeding season in order to keep the 

 eggs separate. Table 2 shows that the hybrid eggs hatched much better than the 

 pure-strain eggs except in the 1935 flock when hatchability was adversely affected 

 by an outbreak of coryza. As the average hatchability at the college plant in 

 1935 was 55 percent, a 75 percent hatchability for the hybrid eggs is evidence 

 of vigor and high hatching power. These hatchability results for 1935 are pre- 

 sented in order that the data may be complete; but from an experimental point 

 of view they are valueless on account of the coryza influence. 



Table 2. — Hatching data— percentage of fertile eggs. 



Evidence of Hybrid Vigor 



It is reasonable to expect less hybrid vigor in the crossing of strains than in 

 the crossing of breeds; likewise less in the crossing of strains that have been 

 bred along similar lines than in those produced under breeding programs where 

 aims and practices are more divergent. Although all flocks involved in this 



