8 MASS. EXPERIMENT STATION BULLETIN 325 



project, with the exception of Flock C, were produced under almost identical 

 breeding programs, yet definite evidence of hybrid vigor is found. 



In the case of body weight and egg size, based upon November and December 

 weights, the hybrid flocks in every instance showed a gain over the average of 

 the parents, the sisters' average being taken as a measure for the sires. Even 

 the January weights, after rigid selection had taken place, indicated hybrid vigor 

 in two cases out of the three in both body weight and egg size. 



In the consideration of hatchability there is no question as to the part played 

 by hybrid vigor, for the hybrid flocks were consistent in the production of eggs 

 having a higher hatchability than those produced by pure lines, and their eggs 

 hatched from 10 to 15 percent better than those from the sires' flock sisters, with 

 the exception of Flock D where coryza greatly influenced hatchability. These 

 data indicate that a hatchability of 79 to 82 percent is about normal for the pure 

 strains used. However, in a project of this kind one cannot be too careful in 

 drawing conclusions as there are two factors that may cause error: first, variations 

 in breeding programs for these flocks; and second, the practical methods used in 

 eliminating undesirable specimens from housing time until the breeding season. 



Summary 



It appears that production qualities and hatchability can be built up or main- 

 tained in a flock by the annual introduction of new blood from reliable sources. 

 Success will depend upon the following factors: 



1. The care with which the foundation flock is selected. 



Only flocks with satisfactory records of performance should be selected 

 for this purpose. 



2. The ability to obtain new blood that will raise the level of the factors sought. 



This should come from breeders who are known to be following an 

 approved breeding program and whose stock is giving a good account 

 of itself either at egg laying contests or in the hands of their clients 

 or both. 



3. The elimination of undesirables before the breeding season begins. 



4. The persistency with which the details of the program are followed. 

 Hybrid vigor made its appearance in egg weights, bird size, hatchability, and 



possibly in production if an accurate measure could have been used. It was not 

 of great significance in bird and egg weights, but of much importance in hatch- 

 ability. 



The cost of this method of flock improvement is insignificant compared with 

 the cost of pedigree breeding, as 300 eggs purchased annually will supply breed- 

 ing males for a flock of 750 females and will also add a possible 100 to 125 quality 

 pullets to the flock. 



Publication of this Document Approved by Commission on Administration and Finance 

 6M-ll-'36. No. £099. 



