absorption, as shown by the biological values, is quite dissimilar, 

 however. This difference in utilization may suggest that better 

 assimilation of this protein, that is utilization, is responsible, 

 at least in part, for the greater nutritive value of PFS in combina- 

 tion with the stepwise higher levels of CL protein. Apparently the 

 PFS protein is more completely utilized when the higher levels of CL 

 are fed because the protein furnished by CL supplies more and more 

 of the lacking amino acids or other nitrogen compounds. 



The problem remains as to the value of more commonly avail- 

 able sources of protein to supplement PFS protein as feed, and the 

 ability of other species of animals to metabolize this protein. 



SUMMARY AND CONCLUSIONS 



Postweaning rats were fed diets containing pollock fish 

 scales (PFS) or a protein supplement of 3 parts casein and 1 part 

 lactalbumin (CL) . The latter also was fed at three levels of protein 

 in stepwise substitution of, as well as in place of, the pollock 

 scales. Apparent digestibilities of protein by individual rats were 

 determined in diets fed during this feeding study. The biological 

 value for maintenance and true digestibility was determined for PFS 

 and CL protein. 



The data indicate: 



1. The mean apparent digestibility is 80 percent when PFS 

 protein is fed at a 9-percent level in the diet to male and female 

 rats. This value of digestibility is not significantly increased 



(p => 0.0$) when rats are fed diets in which the CL protein is sub- 

 stituted in part or in whole for the 9 percent PFS. PFS and CL 

 protein is completely digested, as indicated by true digestibility 

 values, when only enough is fed to equal metabolic nitrogen. 



2. A level of 9 percent PFS protein as the only source of 

 protein in an otherwise adequate diet is incapable of supporting 

 growth in young rats. This nutritional inadequacy of PFS protein is 

 likely due to a deficiency and/or imbalance of specific nitrogen 

 nutrients . 



3. PFS protein can be utilized by rats as a limited source 

 of protein for growth when supplemented with CL protein in the diet. 

 Decreasing ratios of PFS to CL protein in the diet permit progressively 

 better utilization of the PFS protein. 



U. No toxic substances per se are present in pollock fish 

 scales for growing rats. 



5. The biological value of PFS protein for maintaining rats 

 is about 60 percent; which is about 30 percent less than for CL 

 protein. 



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