])etween the two traits were 0.29 at 10 weeks and 0.27 at 6 months of age. 

 Heritahility estimates of hody weight and hreast angle at 10 weeks 

 averaged 50 and 30 percent, respectively, and at 6 months 40 and 25 

 percent. Selection indexes were constructed from these data. The 

 weighting factors determined for the indexes were designed to ohtain 

 maximum progress in both traits. 



Blood Pressure 



Researchers at the New Jersey Agricultural Experiment Station 

 developed an improved method of measuring systolic blood pressure 

 in chickens (50). The new method involved a compact, portable and 

 relatively inexpensive unit which could be easily attached to the bird's 

 shank while in an upright position. 



Selection of lines for high and low systolic blood pressures of White 

 Leghorns resulted in differences between lines after the first generation 

 of selection (55). Cardiac output and stroke volume of hypotensive fe- 

 males were greater than of hypertensive females. However, this did not 

 occur in males. Total peripheral resistance of hypertensive birds of both 

 sexes was greater than that of hypotensive birds and in females the 

 difference was even more striking. Heart rate of the two lines did not 

 differ (53, 54). 



Mortality was greater in both sexes of the low blood pressure line 

 than in the high blood pressure line. This was also true in unselected 

 birds, but the difference in mortality became less when total mortality 

 was low (51) . A similar situation was found with respect to the abilities 

 of the birds of the selected lines to withstand exercise stress (52). In 

 general, the biological efficiency of the birds was better in the high pres- 

 sure line than in the low pressure population. 



Meat Spots 



Data were analyzed from 6 generations of selection for low meat 

 spot incidence in a Rhode Island Red line at the Rhode Island Agricul- 

 tural Experiment Station (31, 32). The number of eggs free of meat 

 spots was increased by 8.7% per generation. The realized heritahility of 

 meat spots was 0.68. This undesirable trait was virtually eliminated 

 from the line. The percentage of hens laying meat-spot free eggs in- 

 creased from none in the zero generation to 37% in generation six. 



However, as the percent of eggs free of meat spots increased, the 

 percent hen-day production decreased by 2.84% per generation. This 

 negative correlated response was significant. Also, a reduction in shell 

 thickness occurred. Correlated responses to percent incidence of meat 

 spots were not detected for age at first egg, egg weight, blood spot inci- 

 dence. Haugh units or albumen height. There were no significant 

 changes in the magnitude of the selection differentials during the experi- 

 ment. 



The population was later mated at random and one group of eggs 

 were stored for 24 hours, another for 12 days at 50 to 55°F. Heritahility 

 of albumen height differences after storage (fresh eggs minus stored 

 eggs for each bird) was estimated, Heritahility estimated from the dam 

 component was 4% at 8 months of age and 18% at 12 months of age. Es- 

 timates from sire components were negative at both ages (30) , 



13 



