protein was more completely balanced by the additional CL. In this 

 case, CL protein could be used for growth when fed alone in the diet 

 at this low level and the PFS protein might be envisioned as contri- 

 buting additional nutrients. 



An increase of yh g. in mean gain was obtained when the 

 group of rats was fed the diet containing 2.25 percent PFS and 6.75 

 percent CL protein over that obtained for the group fed the diet 

 containing 6.75 percent CL protein alone. This increased growth of 

 3U g. is not as great as when the previous pair of diets are compared, 

 namely, 73 g. This result is to be expected, inasmuch as there was 

 less PFS protein in the diet and the nutritively superior CL protein 

 was present in sufficient quantity to permit greater utilization. It 

 is interesting to note that there was a relation of nearly 1:2:1 

 (31, 73 » 3h g.) for the increased growth when the three pairs of diets 

 were fed. This might indicate that the balancing values of the two 

 proteins vary when different levels of each were included in the diets. 



The data in table 1 indicate, in general, that as the rats 

 grew better less protein was required per unit gain in weight. This 

 decreasing requirement for protein suggests that increasing amounts 

 of CL protein permit the rats to utilize the PFS protein more efficiently. 

 "<. r nen this index, as well as the previously compared growth rates, is 

 used as the criteria for PFS protein utilization, trends of data indicate 

 that no toxic substances per se are present in the fish scales. 



The data in table 2 indicate that the mean apparent digesti- 

 bility of PFS protein was about 80 percent when fed at the 9-percent 

 level in the diet. The data also indicate that this level of digesti- 

 bility was not statistically significantly increased (p =) 0.05) when 

 the rats were fed diets in which the CL protein was substituted in 

 part or in whole for 9 percent PFS. 



The increase in digestibility of diets containing the smaller 

 to greater levels of CL protein alone is interesting. It may be that 

 as the rats ingested the stepwise higher levels of food nitrogen, the 

 residual metabolic products eliminated in the feces, as well as the 

 digestibility of the CL protein remained equal. Hence, the ratios of 

 ingested food nitrogen divided by the unabsorbed food nitrogen plus 

 residual metabolic nitrogen would increase. There would be an error 

 in calculating the digestibility of the protein for rats fed a diet 

 containing a small amount of protein which would restrict food intake 

 and limit growth compared with those obtained for rats fed a diet 

 containing an adequate level of protein which would result in increased 

 food intake. and greater growth. 



Biological values for maintenance of 61.2 and 61.1 were gotten 

 for PFS protein with two sets and, similarly, 85.3 and 89. k were gotten 

 for CL protein. The CL protein appears to be utilized about 30 percent 



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