Serum Cholesterol 



An experiment was undertaken at the Maryland Agricultural Ex- 

 periment Station to determine the influence of age during the growing 

 period on levels of serum cholesterol (6). The chicks were from a cross 

 between White Leghorn males and females of a flightless strain of do- 

 mestic fowl. Although serum cholesterol at hatching time was higher 

 by 3 times than at any other time from 1 to 10 weeks of age, the age 

 variation was not significant. 



Differences in serum cholesterol level among dam-families were 

 found when measured in the Cornell randombred population of White 

 Leghorns at 6 to 9 weeks of age (4, 5). Heritability of the trait was 

 estimated to be 0.30. 



After 5 generations of selection the low line was greater than the 

 high line in 6 week body weight, while the Haugh units of the high 

 line exceeded those of the low line. The lines did not differ in advilt 

 body weight, mortality, fertility, hatchability, egg weight, specific gravity 

 of eggs, egg production, or egg yolk cholesterol (59) . 



When the high and low lines were crossed after 5 generations of se- 

 lection, the average cholesterol levels in reciprocal crosses were close to 

 each other and to the average of the two lines. After 6 generations of 

 selection, the cholesterol level of the high line was approximately 30% 

 greater than that of the low line. Liver synthesis of cholesterol was 

 equivalent in the two lines but fecal excretion of the metabolite was 

 greater in the low line (7, 8). 



Correlations were calculated between serum cholesterol of 6 week 

 old chicks and adults and ten other traits (58). The only repeatable 

 and significant phenotypic correlations of serum cholesterol of adult 

 birds were with serum cholesterol at 6 weeks of age ( 4- 0.13) , egg weight 

 ( — 0.13 in October and — 0.18 in March) and albumen quality (—0.24 

 in October and — 0.22 in March) . Genetic correlations of serum choles- 

 terol in young pullets were positive for chick body weight, age at first 

 egg, egg production and albumen quality but were negative for adult 

 body weight. 



Summary 



Much new information was obtained under the second objective of 

 studying genetic correlations. The research on biological selection in- 

 dexes provide a new and imaginative approach to multitrait selection. 

 The estimates of heritability and genetic correlations developed in the 

 project provided bases for new selection indexes designed to maximize 

 overall genetic progress in selection. 



The blood pressure selection project resulted in much new informa- 

 tion of interest to the medical profession as well as to poultry physiol- 

 ogists. The biological efficiency of the high blood pressure line was better 

 than of low pressure birds. The meat spot selection project demonstrated 

 that this undesirable trait can be easily reduced to an insignificant level 

 in a population but egg production and egg shell thickness decreased at 

 the same time. Selection for high serum cholesterol resulted in higher 

 Haugh units but lower 6-week body weight than selection for low serum 

 cholesterol. 



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