. Diet as a factor in length of life and in structure and composition of tissues of the rat with aging. GRAMS \#3 - 600 400 - p' / i d 6 yP^ ! ^ ?a/ 1 1 D 4^ -A ?Ca \#2 A - 200 'a #1. #2. a a SPE A—A SPE n 1 i #3. o o SP 8 1 i HVO i 0 200 400 600 800 1,000 DAYS Figure 2.—Weight in relation to age of selected individual rats fed SP 8 HVO and SPE diets. still more rapid weight gains for animals fed a synthetic diet. Inherent differences in the growth potential of different strains of rats complicate comparison of the size of animals from different laboratories. Mature animals from the stock colo
. Diet as a factor in length of life and in structure and composition of tissues of the rat with aging. GRAMS \#3 - 600 400 - p' / i d 6 yP^ ! ^ ?a/ 1 1 D 4^ -A ?Ca \#2 A - 200 'a #1. #2. a a SPE A—A SPE n 1 i #3. o o SP 8 1 i HVO i 0 200 400 600 800 1,000 DAYS Figure 2.—Weight in relation to age of selected individual rats fed SP 8 HVO and SPE diets. still more rapid weight gains for animals fed a synthetic diet. Inherent differences in the growth potential of different strains of rats complicate comparison of the size of animals from different laboratories. Mature animals from the stock colony maintained in this laboratory appear to weigh as much as or more than most stock rats of comparable age from other laboratories. Their average maximum weight was slightly less than the 522 grams re- ported for the rapid-growth-producing diet of Anderson and Smith (.9). Rats fed the semipuri- fied diet reached weights comparable to those observed by Mayer (127) using a synthetic diet. Numerous equations have been suggested to represent changes of weight with age, and several investigators (44, 58, 78) provided evidence for the usefulness of the equation proposed by Zucker, Hall, Young, and Zucker (194) for evaluating rat growth and relative efficiency of various experi- mental diets. These authors proposed an empiri- cal formula for expressing growth which defines K, a growth intensity factor, and A, an inherent size factor. When the formula was applied to data from their laboratories as well as to data from other laboratories, these authors report that a straight line was generally observed and that neither size nor growth rate appeared to affect the growth property measured by K, the slope of the line, as long as the diets were free from growth- inhibiting factors. Dunn, Murphy, and Rock- land (53), however, observed a change in the GRAMS 600 400 200 74 56 34 24 69 / <\_~v 13. 21 12 , 3 ^o-O-0^. LONGITUDINAL DATA* a—a SP 8 HVO o—-o SPE CROSS-SECTIONAL DATA** —o
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