38%. However, this increase was not significant, suggesting that laying 

 hens prevent a marked hypercholesterolemia by excreting it in the yolk. 



Embryo Weight 



At the New Hampshire Agricultural Experiment Station, controlled 

 matings were made from meat-type chickens previously selected for 

 8- week body weight (60) . Hatching eggs were incubated and the embryos 

 were weighed 14 days later. Significant line and sire differences in 14 

 day embryo weights were found. 



Feed Efficiency 



Studies of the efficiency of feed utilization for egg production were 

 conducted at the Maine Agricultural Experiment Station. Distinct possi- 

 bilities were revealed for the selective improvement of the trait. Herit- 

 ability estimates were in the range of 30 to 50 %> when feed utilization 

 figures were corrected for egg mass, body weight, and body weight 

 changes during the test period. 



Immunogenetics 



Wlien rabbits were immunized to chicken blood at the Connecticut 

 Agricultural Experiment Station, a difference was found in the reaction 

 of rabbit antisera to the blood plasma of New Hampshire, Rhode Island 

 Red, Leghorn and Cornish chickens ( 1 ) . However, individual chickens 

 of the same breed could not be distinguished on the basis of their 

 plasma antigens with the techniques used. 



Summary 



The greatest activity in NE-6 was on the third objective of deter- 

 mining the physiology of gene action and much progress was made. 



In a study of 14 day embryo weight, important line and sire differ- 

 ences were described. A feed efficiency study revealed highest herit- 

 ability estimates when the data were corrected for egg mass, body weight, 

 and body weight changes during the test period. Different breeds of 

 domestic fowl were found to differ in their plasma antigens and some 

 protein components repeatedly showed close relationships with short 

 term egg production. 



Several interesting relationships of plumage color genes with other 

 traits were noted. The gene for extension of black pigmentation was 

 associated with high mortality, dominant white birds had superior egg 

 production, colored birds were heavier at 8 weeks of age than recessive 

 white birds, and autosomal barring was associated with social domin- 

 ance. Yellow shank pigmentation was shown to have medium to low 

 heritability. Considerable difficulty was encountered in searching for a 

 good measure of thyroid gland activity. Egg yolk cholesterol was a high- 

 ly variable trait easily influenced by diet and season, and no sire or dam 

 influences could be detected. 



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