Conversion of Dietary to Body Energy in Rats as Affected by Strain, Sex and Ration

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Abstract
Weanling male Osborne-Mendel (OM) rats fed, for 10 weeks, a nutritionally complete ration containing 60% (w/w) of a vegetable shortening deposited 285 ± 20 kcal in their carcasses for every 1000 kcal consumed. Littermates fed a grain ration containing 3% fat deposited 129 ± 7 kcal in their bodies for every 1000 kcal consumed during the 10-week period. Extending the feeding period an additional 10 weeks to 20 weeks reduced the percentage of dietary energy retained in the carcass. This reduction was slightly greater for the grain-fed than for the high fat-fed OM rats. Male weanling rats of the S 5B/Pl strain in the first 10 weeks of the study deposited 100 ± 15 and 128 ± 14 kcal in their bodies for each 1000 kcal consumed from the grain and high fat rations, respectively. Regardless of the type of ration fed, food energy unaccounted for in carcass retention was similar for rats of the same sex, age and strain. For each ration. OM rats ate one-third again as much as S 5B/Pl rats. Female rats deposited only 70% as much dietary energy in their carcasses as did males. This percentage differential between males and females existed for both strains of rats fed either ration and for both the 10- and 20-week periods. Female rats of both strains converted two-thirds as much dietary protein to carcass protein as did the males.