Influence of Plane of Nutrition on Body Composition, Organ Size and ...

ENERGY UTILIZATION DURING REALIMENTATION 25271800 h. Body weights were taken twiceweekly. Daily feed intake <strong>of</strong> individual animals was adjusted twice weekly based onactual body weights and targeted weightssuch that the planned gains or losses wereachieved. A premeasured amount <strong>of</strong> feed(Purina Rat Chow) was given to each animal at 1600 h each day and unconsumedfeed was removed at 0800 h the followingmorning. Weight <strong>of</strong> unconsumed feed wasrecorded daily. All animals had free accessto water at all times.During period 2, total excretion <strong>of</strong> urineand feces <strong>of</strong> 24 animals randomly chosenacross the eight treatment groups was collected for 3 d for determination <strong>of</strong> the metabolizableenergy content <strong>of</strong> the diet.Statistical analysis <strong>of</strong> the results did notreveal any significant differences due to sexor feeding level. Therefore a mean value <strong>of</strong>2.91 kcal/g was adopted as the metabolizableenergy content <strong>of</strong> the diet forcalculation <strong>of</strong> ME intakes.Data were analyzed by analysis <strong>of</strong>variance and regression procedures (22).The effect <strong>of</strong> sex on body composition traits<strong>of</strong> rats killed at the initiation <strong>of</strong> the studywas evaluated by one-way analysis <strong>of</strong>variance. The relationship between bodyprotein, body fat or energy content andbody weight was evaluated by use <strong>of</strong> amodel that included sex, body weight (BW,linear and quadratic) and all two-way interactions as independent variables. Nonsignificant independent variables were deletedstepwise in subsequent analyses.The effects <strong>of</strong> sex and treatment duringperiod 1 on food consumption, bodyweight, body composition, rate <strong>of</strong> gain andcomposition <strong>of</strong> gain were evaluated by twowayanalysis; the model included treatment, sex and the two-way interaction asindependent variables. Treatment groupmeans were compared by Student's f-test ifthe analysis <strong>of</strong> variance indicated significant treatment differences. The relationships between empty body weight, water,protein, fat, ash or energy and BW were determined by procedures like those describedabove.Data obtained during and at the end <strong>of</strong>period 2 were also analyzed by analysis <strong>of</strong>variance. The model includedsex and the two-way interactiontreatment,as independent variables. Student's i statistic was usedfor comparison <strong>of</strong> specific means (i.e, rats<strong>of</strong> the same sex and final weight group or <strong>of</strong>the same sex and rate <strong>of</strong> gain during period2) if analysis <strong>of</strong> variance indicated significant (P < 0.05) treatment or sex x treatment effects. Multiple linear regressionanalyses were used to describe relationships<strong>of</strong> visceral organ weights to empty bodyweight and average daily weight gain during period 2. Sex and its two-way interactions were included as independentvariables to test sex effects on these relationships. The model proposed by Koong andHill (22) was used to evaluate relationships<strong>of</strong> daily empty body energy gain (kilocalories)to average metabolic body size (kilograms empty body weight 0.75)and dailymetabolizable energy intake (kilocalories).Sex and previous nutritional treatment(treatment during period 1) as well as alltwo-way interactions were included in theinitial model to evaluate their effects onthese relationships. Estimates <strong>of</strong>maintenance [metabolizable energy required for zero body energy change,kcal/(kg°75-d)3 were calculated from theresulting equations after setting energychange to zero.RESULTSWeight and composition <strong>of</strong> male andfemale rats killed at the initiation <strong>of</strong> thestudy are presented in table 1. No significant differences (P > 0.10) between malesTABLE 1Least squares means for initial weight andcomposition <strong>of</strong> male and female ratsTrait Male FemaleRSD'No. animalsLiver <strong>of</strong>gEmptyweight,gBody body,gBodywater,gBodyfat,gBodyprotein,gBodyash,energy, kcal686.374.253.44.213.72.56120975.164.446.43.511.92.2910312.9712.078.'Calculatedas the square root <strong>of</strong> the error meansquare and based on 13 error degrees <strong>of</strong> freedom. Standard error may be calculated as RSD/VNjDownloaded from jn.nutrition.org by guest on August 9, 2014