Feed efficiency and body composition of selected and unselected mice

Summary An examination was carried out of the feed intake, feed efficiency and body composition of selected and unselected mice. It was demonstrated that selected mice utilised food more economically, and, in total, produced more protein than the control animals. However, selection had a negative influence on the percentage content of protein and ash. Also, selection caused greater adiposity of selected females and a greater water content in the bodies of selected males (in %).This work was partly supported by grant No. FG-Po-348 (JB-13), Project No. PL-ARS-68.     

QTLs for pre- and postweaning body weight and body composition in selected mice

In an intercross between the high-body-weight-selected mouse line NMRI8 and the inbred line DBA/2, we analyzed genetic effects on growth during the suckling period and after weaning during the juvenile phase of development. QTL mapping results indicated that a switch of gene activation might occur at the age of three weeks when animals are weaned. We found QTLs for body weight with major effects at the age of two and three weeks when animals are fed by their mothers, and QTLs with highest effects after weaning when animals have to live on their own under ad libitum access to food. Specific epistatic effects on body weight at two and three weeks and epistatic interaction influencing growth after weaning support this finding. QTL effects explained the greatest variance during puberty when animals grow fastest and become fertile. In the present study, all except one QTL effect for early body weight had dominance variance components. These might result from direct single-locus-dominant allelic expression, but also from the identified epistatic interaction between different QTLs that we have found for body weight at all ages. Beside body weight, body composition traits (muscle weight, reproductive fat weight, weight of inner organs) were analyzed. Sex-dimorphic QTLs were found for body weight and fat deposition. The identified early-growth QTLs could be the target of epigenetic modifications which might influence body weight at later ages.     

The activity of certain enzymes in the liver of mice,selected for weight gain

Summary Examining the weight gains of mice in selected and nonselected lines maintained on a low (10%) and high (20%) protein diet, and of their crossbreds, it was ascertained that the highest values occurred in selected lines maintained on a high protein level and the lowest in crossbreds.Analysing the enzyme activity — aldolase, aminotransferase AspAT and AlAT — in the liver of these animals, it was observed that selected mice maintained on either of the protein levels demonstrated usually values significantly lower than for the nonselected ones.     

Changes in growth,appetite, food conversion efficiency and body composition in mice selected for high post-weaning weight gain on restricted feeding

Summary This study aimed to test the hypothesis that if animals were fed the same amount over the same time period, selection of the fastest growers would result in a change in the partitioning of metabolisable energy toward more protein and less fat deposition. Two mouse lines (S1 and S2) were selected for high 5 to 9 week weight gain corrected to mean 5 week weight. Appetite variation between mice was eliminated by feeding a fixed amount to each mouse daily. After 6 generations of selection, the lines were compared with an unselected control (C) on restricted and ad libitum levels of feeding for growth rate, appetite, food conversion efficiency and chemical body composition.Realised heritabilities of 5 to 9 week gain were 0.36+ 0.05 and 0.19±0.04 for S1 and S2 respectively. Nine week weights were increased by an average of 13% on both feeding levels. Most of this increase, particularly in S2, occurred before 5 weeks and was therefore outside the period of measurement used in selection. On ad libitum feeding, selection increased food intake per unit time by 6% but there was no increase per unit body weight. Food conversion efficiency (gain/food) increased by 12%. Compared with controls at 9 weeks, 3% more of the body weights of selected mice was fat and 1% less was protein. These differences were reduced but were still in the same direction when comparisons were made at the same body weight. Thus the expected change in energy partitioning toward greater protein and less fat deposition in the S lines did not occur.It was concluded that the increased growth and energy retention in the S lines was brought about by a reduction in maintenance requirement. To achieve the desired change in energy partitioning using a similar selection scheme, higher levels of dietary protein should be fed, and some measure of protein deposition rather than growth rate used as the selection criterion.     

Growth and body composition changes in mice selected for high post-weaning weight gain on two levels of feeding

Summary Two lines of mice were selected for high post-weaning weight gain (3 to 6 weeks) adjusted for 3 week weight. One line (F) was grown on freely available food and the other (S) on a feeding scale set at the same level for all mice. Food intake of the S line averaged 80% of the F line. The realised heritabilities after 6 generations of selection were 0.38±0.06 and 0.33±0.07 for the F and S lines, respectively. In generation 7, mice from the F and S lines and from an unselected control line (C) were compared on both free and set levels of feeding from 3 weeks to 9 weeks of age. Measurements taken were growth rate, appetite, food conversion efficiency (weight gain/food intake) and body composition (fat, protein, ash, water). The F and S lines grew more rapidly and efficiently than the C line on both levels of feeding, each line performing best on the level of feeding on which it was selected. The average genetic correlation between growth rates of the same line on the two feeding levels was 0.54±0.10. The F line grew 19% faster and was 9% more efficient than the S line on free feeding but the S line grew 15% faster and was 15% more efficient than the F line on set feeding. Relative to the C line, food intake per day on free feeding was 4% higher in the F line and 6% lower in the S line. There was no difference between the lines in food intake/g body weight. The rate of deposition of all body components increased in both selection lines. In the F, S and C lines respectively, efficiencies of gains in body components (10²x gain/food) were 1.79, 1.31 and 1.06 for fat, 1.53, 1.63 and 1.22 for protein and 5.88, 6.45 and 4.98 for protein + water. Apparently energy lost as heat was reduced in both the F and S lines. The partitioning of energy retained was altered in favour of more fat in the F line and more protein in the S line.     

Milk yield in lines of mice selected for growth or maternal ability.

Two experiments were conducted to measure milk yield as a correlated response to selection for increased 12-day litter weight (maternal lines) for 13 generations and increased and decreased body weight gain from 21 to 42 days of age (postweaning gain lines) for 12 to 14 generations. Milk yield was measured from day 6 to day 21 of lactation by separating litters from their dams for 6 h, then weighing litters before and after a 1.5 h suckling period. Average total milk production was 30.3 +/- 0.9 g and 28.6 +/- 1.1 g in maternal and control lines, respectively. This difference was not significant (P greater than 0.05). Differences among gain lines were significant (P less than 0.01) in the second experiment with average production of 44.1 +/- 1.4 g for increased gain lines, 22.5 +/- 0.9 g for the decreased gain line and 31.2 +/- 1.0 g for the control. These results indicated that response to selection for increased 12-day litter weight was not associated with increases in milk yield, but sizable changes inmilk yield accompanied bi-directional selection for early postweaning gain.     

Inbred lines of mice derived from long-term growth selected lines: unique resources for mapping growth genes

Lines of mice selected for many generations for high or low growth in several laboratories around the world have been collected, and from these, inbred lines are being developed by recurrent full-sib mating in Edinburgh. There are seven high selected lines and four low lines (each low line is from the same base population as one of the high lines), and the histories of each are summarized. Mean body weight of males at 70 days of age in the Edinburgh laboratory in the heaviest inbred line (77 g) is 4.8-fold higher than in the lightest line (16 g), and 1.9-fold higher than in the least extreme high line (41 g). Litter size, food intake, and fat content also differ substantially. These inbred extreme selected lines are a uniquely valuable resource for QTL or gene mapping, candidate gene identification, and elucidation of epistatic effects. Received: 19 February 2001 / Accepted: 3 May 2001     

Biochemical and immunological changes in mice following postweaning copper deficiency

Weanling albino male mice rapidly develop biochemical signs of copper deficiency when fed a purified diet containing 0.5 mg Cu/kg. Plasma ceruloplasmin activity of copper-deficient (-Cu) mice was 5% of that of copper-adequate (+Cu) control mice after only 3 d on the diet. More gradual loss of organ (liver, spleen, and thymus) cytochrome c oxidase activity was observed during the next 4 wk. Body weight was equivalent between +Cu and -Cu mice, but thymus weight dropped faster in -Cu mice than +Cu mice. The number of antibody producing cells to sheep erythrocytes was lower in -Cu mice compared to +Cu mice after 17 d on the diet. Spleen cytochrome oxidase activity of -Cu mice was 50% of that of +Cu mice by 10 d on the diet. Mitogenic response of splenic and thymic lymphocytes to concanavalin A (con A) was not greatly different between +Cu and -Cu mice. Splenocytes from -Cu mice had a 3-fold higher thymidine incorporation rate in the absence of mitogen compared to +Cu mice. The depressed antibody and high mitogenic background responses of -Cu mice were similar to previous work with another strain (C58) of mice that had been started on copper-deficient treatment from birth. However, the normal proliferative response to con A stimulation in postweaning copper deficiency differs from the previous model. Mice of both studies were very copper-deficient as judged by liver copper levels. Timing of the copper-deficient treatment influences the manner in which copper deficiency alters the immune response.     

Body growth and substrate partitioning for fat and protein gain in weaned BALB/c mice treated with growth hormone

Previously we have found that recombinant human growth hormone (rhGH) (GH; 74 ng g body wt.(-1)) administration to weaned BALB/c male mice (fed 12% or 20% protein diet) induced a growth lag and subsequent repletion similar to the catch-up growth process. We studied the partitioning of feed and protein intakes between adipose and protein body stores through the linear relationships among them. The non-linear relationship of protein intake with body fat gain/protein gain (FG/PG) ratio was especially adequate in determining the partitioning of substrates. rhGH induced an increase in feed and protein intake utilization for body weight gain (50%) and fat gain (75-140%) over saline; macronutrient utilization was the greatest in rhGH-treated mice fed 20% protein. However, growth recovery of rhGH mice was anomalous and protein intake was derived primarily for fat gain. Mice fed 12% protein (treated and control) also derived protein intake in preference to fat stores. Treatment and diet had a cumulative effect with the result that rhGH-treated animals fed 12% protein showed the greatest FG/PG ratio (1.6), and therefore, the lowest efficiency to gain protein. Weaning is a critical stage in mice when treating with rhGH, as this could provoke a growth lag. The study showed that a high protein level is required to surpass the rhGH-induced lag, but it is not enough to obtain an enhanced protein deposition. Feeding a 12% protein diet was even worse as mice did not improve on the growth lag and substrates were directed mainly to body fat.     

Rate,composition and efficiency of growth in mice selected for large and small body weight

Summary Mice selected for high (H₆) and low (L₆) 6-week body weight and a randombred control population (C₁) were characterized for rate, composition and efficiency of growth. Individual body weights were obtained from birth to 8 weeks of age on 682 mice representative of the three lines. Individual whole carcass determinations of water, fat, ash and protein (residual) were obtained for 180 mice sampled weekly from 3–8 weeks of age. Efficiency of feed utilization was estimated from individual body weight and feed consumption data obtained on 189 mice from 3–8 weeks of age. Growth curves for body weight and gain in body weight, constructed by line and sex, showed a temporary retardation of maximum growth rate in the L₆ line, which was attributed in part to an extended depression in growth following weaning. The composition of growth yielded no evidence that the more rapid growth rate in the H₆ line resulted from an increase in fat deposition relative to the other carcass components. A decrease in fat percent at 7 weeks of age in the H₆ and C₁ lines was not evident in the L₆ line until 8 weeks of age. Females had a higher percentage carcass fat than did males during the 4–7 weeks growth period, but this difference was essentially reduced to zero by 8 weeks of age. Percentage water was highly correlated negatively with percentage fat. Percentages protein and ash were essentially constant across lines and ages. A positive relation between rate and efficiency of growth was observed between lines. Consistent sex differences, males more efficient than females, were observed prior to 6 weeks of age, but were not evident in the later (6–8 week) data.

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Zusammenfassung Bei Mäusen, die auf hohes (H₆) und geringes (L₆) 6 Wochen-Körpergewicht selektiert waren, und einer unselektierten Kontrollpopulation (C₁) wurde die Zuwachsrate, die Veränderung des Wasser-, Fett-, Protein- und Aschegehaltes während des Wachstums sowie die Wuchsleistung untersucht. Das Körpergewicht von der Geburt bis zum Alter von 6 Wochen wurde an 682 einzelnen Mäusen, die repräsentativ für die drei Linien sind, festgestellt. Die Ermittlung des Wasser-, Fett-, Asche- und (Rest-)Proteingehaltes der Tiere erfolgte wöchentlich für 180 Mäuse im Alter von 3–8 Wochen. Die Futterverwertung (Wuchsleistung) wurde für 189 drei bis acht Wochen alte Mäuse auf Grund von Einzelgewichten und Futterverbrauch geschätzt.Die Wachstumskurven für Körpergewicht und Gewichtszunahme, nach Linien und Geschlecht zusammengestellt, zeigten bei der L₆-Linie eine zeitweilige Verzögerung der maximalen Zuwachsrate, was z. T. einer längeren Wachstumsdepression nach der Entwöhnung zugeschrieben wird. Es ergab sich kein Beweis dafür, daß die schnellere Wachstumsrate bei der H₆-Linie auf eine Erhöhung der Fetteinlagerung im Verhältnis zu den anderen Komponenten zurückzuführen ist. Ein Rückgang des Fettgehalts, der bei den H₆- und C₁-Linien im Alter von 7 Wochen festzustellen war, wurde bei der Linie L₆ erst nach 8 Wochen sichtbar. Weibliche Tiere hatten im Alter von 4–7 Wochen einen höheren Körperfettgehalt als männliche, im Alter von 8 Wochen war dieser Unterschied aber nicht mehr vorhanden. Der Wassergehalt war in hohem Maße negativ mit dem Fettgehalt korreliert. Die Protein- und Ascheanteile waren im wesentlichen für die Linien und untersuchten Wuchsperioden konstant. Zwischen den Linien wurde eine positive Relation hinsichtlich Wuchsrate und Wuchsleistung festgestellt. Deutliche Geschlechtsunterschiede wurden bis zum Alter von 6 Wochen beobachtet, und zwar wuchsen die Männchen schneller als die Weibchen, später (6.–8. Woche) waren keine Unterschiede mehr feststellbar.

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Paper number 2640 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh, North Carolina. Supported by Public Health Service Grant GM 11546-05. Computation was supported by NIH Grant No. FR-00011. The senior author was supported by NIH Training Grant No. 2-Tl-GM-296.     

Log-normal variation belts for growth curves

Prediction (confidence) or tolerance belts compound the uncertainty of sample estimates with the estimated extent of individual variation. The latter is therefore better described by variation belts, in which sample estimates are simply substituted for population parameters. Variation belts can provide valuable graphical indications concerning the goodness of fit of postulated error models. While multiplicative least-squares (MLS) methods appear appropriate in principle for biological growth, they are unsatisfactory in practice when logarithmically transformed data are heteroscedastic. Heteroscedastic multiplicative error models can be fitted by iteratively reweighted multiplicative least squares (IRMLS), but unacceptable negative or infinite residual variance estimates and unreasonably wide variation belts are occasionally obtained. These difficulties can be prevented by constrained iteratively reweighted multiplicative least squares (CIRMLS). Examples are presented concerning the metabolic allometry of white rats, the somatic growth of male elephant seals, and the growth of an experimental population of Paramecium caudatum.