DIET: SPM 



DIET: SPB 



DIET: SPPB 



% DYING 



30 



20 



10 







< 4 5 6 7 > 



1 > 



< 4 56 7 > < 4 56 



AGE (hundred days) 



Figure 5. — Percentage of total number of rats dying within different age intervals on SPM, SPB, and SPPB diets. 



The average length of life of rats fed SP 16 

 butter diet was less than that observed on SPM 

 diet. The type and level of protein in these two 

 diets were the same; mineral content as well as 

 level of fat was similar. The major differences 

 between these diets were the presence of 6 percent 

 HVO and of 5 percent lactose from the dried skim 

 milk in SPM diet, whereas all of the fat in SP 16 

 butter was from butter and all of the carbohydrate 

 was sucrose. The presence of lactose may have 

 been a factor contributing to the difference in the 

 survival on the two diets, although the amount 

 was low in comparison with the 39 percent sucrose 

 in this diet. No antioxidants were added to 

 these diets, and the tendency for somewhat re- 

 duced consumption of the SP 16 butter diet may 

 be related to lower stability of the fat in this diet. 

 The content of the low-molecular fatty acids (C u 

 and below) in the SP 16 butter was higher, about 

 twice that of the SPM diet. Data available pro- 

 vide no answer as to the cause of the differences 

 observed. 



Protein level. — Modification of the semipuri- 

 fied diet by increasing the protein or the protein 

 and fat level to that of SPE diet resulted in no 

 significant change in the lifespan of these rats. 

 Respiratory infection was responsible for some of 

 the early deaths of the small group of eight litter- 

 mates fed SPa 16 HVO and SPb 8 HVO diets; 

 no difference in survival was apparent for the 

 larger group of littermates fed SP 8 HVO and 



SPa 16 HVO diets. The results with SPb 8 

 HVO and SPa 16 HVO were similar, suggesting 

 again that increasing the level of HVO from 8 to 

 16 percent was without effect on survival. 



Egg and egg components. — Rats fed a diet 

 containing a relatively high level of egg white 

 (SPEW) and those fed a diet consisting of 100 

 percent whole egg survived longer than those fed 

 a diet containing 25 percent egg (SPE) or 30 per- 

 cent egg yolk (SPEY). The lifespan of rats fed 

 SPEW was similar to that observed for those fed 

 the modified semipurified diet (SPa 16 HVO) with 

 comparable levels of fat and protein, whereas the 

 average age at death for rats fed SPEY diet was 

 similar to that obtained for littermates fed the 

 SPE diet containing cooked fresh egg. The 

 survival period of rats fed 100 percent egg yolk 

 was short. No data were obtained on longevity 

 of rats consuming 97 percent egg yolk and 3 per- 

 cent salt mixture, but other results obtained with 

 this diet, to be considered more fully later, suggest 

 that the lifespan of rats fed this high egg yolk diet 

 may be increased appreciably when the diet is 

 supplemented with a suitable salt mixture. 

 Although some of these data seem to indicate 

 that it is the yolk of egg that is contributing to 

 the shortened lifespan of rats fed SPE diet, the 

 finding that rats tolerate diets containing 100 

 percent egg better than a diet containing either 

 25 percent whole egg or 30 percent egg yolk 



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