more than PFS protein. True digestibilities determined in this test 

 indicated that both PFS and CL protein were completely digested. 

 Whereas the apparent and true digestibility of the two proteins by 

 rats are similar, quite different assimilation is indicated by the 

 biological values. 



DISCUSSION 



Investigators studying the nutritive value of other waste 

 scleroproteins have concluded that they are nutritionally inadequate, 

 but can be used as a partial source of protein with proper supplementa- 

 tion. This conclusion is also true with pollock fish scale protein. 



Rats fed a diet containing 9 percent protein from PFS alone 

 lost considerable weight and died in about 8 weeks. Rats fed diets 

 containing PFS in combination with stepwise higher levels of CL protein, 

 for a total dietary protein level of 9 percent, however, utilized the diet 

 for growth increasingly better. These rats also grew better than those 

 fed the stepwise higher levels of CL protein alone in the diet. In 

 general, as the rats grew better they utilized the food for growth more 

 efficiently. 



Routh (l9U2a, 19ii2b), Wagner and Elvehjem (19U2, 19h3), Newell 

 and Elvehjem (I9h7) , Wilder et al. (1955), and others showed that the 

 various nutritively deficient scleroproteins could be utilized or 

 balanced with proper supplementation, but in general they did not 

 indicate that this utilization or balance could be improved when greater 

 levels were included in the diets. In most cases the supplementations 

 consisted only of empirical amounts of amino acids added to the diet 

 in order to find out which acids alone or in combination permitted 

 better utilization of the scleroprotein. 



The rats fed the diet containing a 9-percent level of protein 

 from CL alone grew better than rats fed any other 9 percent protein 

 combination of PFS and CL protein. At this level of protein in the 

 diet, at least, CL protein must be better balanced in nitrogen nutrients 

 than the protein from any of the combinations. Thus, the growth of 

 rats fed diets containing increasing levels of PFS protein in relation 

 to fixed levels of CL protein was less and less. Toxic factors, per se , 

 in the scales must be ruled out, because there then would be no varia- 

 tion in the utilization of PFS protein by the rats. Furthermore, there 

 were no visible symptoms of toxicosis. 



The protein of the fish scales is digested sufficiently 

 well so this cannot be an important factor in explaining the effects 

 noted. The results showed that, at the 9-percent level in the diet, 

 both PFS protein and CL protein were about 80 percent digested when fed 

 to rats. This high level of digestion indicates that the incomplete, 

 probably imbalanced, PFS protein had been absorbed to a considerable 

 extent and was available for metabolism. The utilization after 



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