Organ growth of selected lines of chickens and their F1 crosses to a common body weight or age

Summary Organ growth of male chickens selected for high and low 56-day body weight and their reciprocal F₁ crosses was compared at a common age (56 days) or at a common body weight (180 g). Organs that differed at a common body weight included weights of proventriculus, small intestine, lungs, feathers and abdominal fat and length of esophagus. Organ weights that differed at a common age included esophagus, gizzard, heart, liver, lungs, breast, legs, feathers and abdominal fat, and lengths of shank, esophagus and small intestine. Heterosis for most organs was less than 15%. Those exhibiting heterosis greater than 30% included weights of fat depots and feathers, plus lengths of the esophagus, small intestine and shank. Heterosis for these traits, however, varied depending on whether comparisons were made at common body weight or age. These results imply that biological functions of organs at specific ages may not reflect the situations at common body weights and suggest differences in resource allocations among populations.     

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.     

Growth,feed efficiency and lifetime performance of crosses between lines selected for nursing ability and/or adult weight in mice

Summary Two populations of randombred of different origin (P and Q) containing eight lines (M_P, W_P, B_P, C_P, M_Q, W_Q, B_Q and C_Q) were used to evaluate the growth, feed efficiency and lifetime performance of females from eight pure lines and 16 F₁ crosses. Line comparisons within populations (P or Q) revealed that the heaviest line at days 21, 42 and 63 was W, followed by lines B, M and C in both populations, while the highest in feed efficiency between days 21 and 63 was line W, followed by lines B, M and C in population P, and was line B followed by lines W, M and C in population Q. Generally, average body weights and feed efficiencies of crosses within and between populations were similar to those of mid-parents. Selection produced line W superior to the line M in additive direct genetic effects on body weight and feed efficiency in each population, and line W_P superior to line W_Q in additive maternal genetic effects on body weights at days 21, 42 and 63. In lifetime performance tests, total 20-day weight of litters produced by a dam during 200 days averaged from 442.7 g (W_P) to 739.1 g (M_P) for the eight lines. Lines M and W of populations P and Q generally did not differ in additive direct and maternal genetic effects on lifetime performance. Crosses excelled lines in the number of litters raised to weaning (5.44 vs. 5.25) and total 20-day litter weight per dam during 200 days (648.5 vs. 589.3 g). For lifetime 20-day litter weight per group, crosses from unselected lines (C) exceeded crosses from lines selected for nursing ability (M), adult weight (W) and both traits (B). Crosses of lines from different populations showed a higher heterosis in lifetime performance than crosses of lines within populations. Heterosis in the number of litters raised to weaning, and total 20-day litter weight per dam was significant in crosses between lines C_P and C_Q, between lines W_P and w_Q, and between lines W_P and m_Q. Crosses C_PC_Q and C_QC_P had a highly persistent production during lifetime tests.Animal Research Institute Publication 860USDA SEA-AR, Purdue University, West Lafayette, In. 47906 (USA)     

Correlated responses in growth and body composition of replicated single-trait and index selected lines of mice

Summary Correlated responses in growth, body composition and efficiency were evaluated in lines of mice selected in the following ways: W⁺T _i ^o , increased six-week body weight (WT6); W ° T _i ⁺ , increased six-week tail length (TL6); W⁺T _i ^– , increased WT6 and decreased TL6; W^–T _i ⁺ , decreased WT6 and increased TL6; M16, increased three-to six-week postweaning gain (PWG). Each of the first four selection treatments had two replicate lines (i = 1, 2) selected for 13 generations and the fifth treatment had one line selected for 30 generations. All lines were derived from a randombred ICR albino population which served as a control. Additional traits studied were three-week body weight and tail length, postweaning gain in tail length, percent body composition (ash, fat, moisture and protein) at six weeks of age, and three-to six-week feed consumption (CONS) and efficiency (EFF = PWG/CONS). Efficiency of body constituent gains (ash, fat, protein and caloric value) were determined by dividing each constituent by CONS. Relative to selection treatments, replicate variation in the array of traits was small and was primarily attributable to the effects of genetic drift; more frequent significant replicate differences among traits in W⁺T^– were associated with a replicate difference in cumulative selection differentials. Selection for different criteria involving WT6 and TL6 did not change the allometric relationship between tail length and body weight in the three-to six-week age interval. The significant divergence between W⁺T ° and W °T⁺ and between W⁺T^– and W^–T⁺ was as expected for WT6 and TL6. Significant asymmetry of selection response between W⁺T^– and W^–T⁺ for WT6 and TL6 was attributed to maternal effects. In agreement with theory, antagonistic index selection generally yielded smaller genetic responses than single trait selection. Positive correlated responses in CONS and EFF were found for M16 and W⁺T °. Significant correlated changes in CONS (positive in W °T⁺ and negative in W^–T⁺) were not accompanied by a significant change in EFF. In contrast, W⁺T^– evinced an increased EFF and no change in CONS. Percent fat increased significantly in W⁺T ° and M16. For W⁺T^o, W⁺T^– and M16, an increased energetic, fat and ash efficiency was observed, whereas M16 exhibited a positive increment in protein efficiency as well. Among selection treatment means, there were high positive correlations between WT6 and fat weight, protein weight, percent fat, CONS and EFF and a high negative correlation between WT6 and percent protein.Paper No.4916 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, N.C. 27607. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Experiment Station of the products named, nor criticism of similar ones not mentioned.     

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.     

Body weight and tail length divergence in mice selected for rate of development

A series of mouse lines has been produced by 19 generations of restricted index selection for rate of development during early and late ontogeny. The selection program was based on an index with the following four replicated selection treatments: E(+) and E(-) were selected to alter birth to 10-day body weight gain while holding late gain for both selection lines constant; correspondingly, L(+) and L(-) were selected to alter 28- to 56-day body weight gain holding early gain for both lines constant. Herein, we characterize response to selection for growth rate by analyzing age-specific mouse body weight and tail lengths and for growth curves using a logistics model. Selection on developmental rate has resulted in divergence in both age-specific and growth curve traits. E(+) and L(+) lines reached identical weights during the late selection interval, then diverged to unique mature weights. E(-) and L(-) lines similarly achieved identical weights during late selection and diverged to unique mature weights. However, the shapes of early and late growth curves were significantly divergent, and at least two distinct growth patterns are shown to result from selection. Response in body weight gain was accompanied by similar, though less pronounced, change in tail length traits. Significant response during intervals of restricted growth was also found, especially in lines selected for late gain. The evolution of the growth trajectory under restricted index selection is discussed in terms of drift and available additive genetic variation and covariation.     

Body weight and growth rate in laboratory lines ofPoecilia reticulata reared on two different diets

Summary Body weight and growth rate of fish from three laboratory lines fed with two different diets have been analyzed. The differences in response to the diets seem to be related to the different degree of genetic homogeneity of the lines considered. The most homogeneous line shows the greatest variation under the two diets for average body weight at 30 and 70 days as well as for growth rate. An effect of the parents' diet on their offspring was also observed. The increase in growth rate observed when fish are fed with the live food diet is amplified when the progenies derive from parents fed with the dry food diet. Moreover, an effect due to the mother's size is also evident on the mean values of body weight at 30 days. The persistence of this maternal effect on the offspring phenotype during post-embryonic development seems to depend on the degree of genetic homogeneity of the line considered-being the greatest in the most homogeneous line.     

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     

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.     

Influence of early pregnancy on reproductive rate in lines of mice selected for litter size

Summary The influence of male-induced early puberty on female reproductive rate was determined in three lines of mice differing in litter size and body weight. The lines originated from a single base population and had undergone 20 generations of selection for the following criteria: large litter size at birth (L⁺), large litter size and small 6-week body weight (L⁺W^–), or small litter size and large 6-week body weight (L^–W⁺). Females were paired with a mature intact male of the same line at 3, 5 or 7 weeks of age. Mean mating age, averaged over lines, was 26.5 ± .3, 38.3 ± .3 and 52.7 ± .3 days. Exposure to a mature male accelerated female sexual maturation in each line. When contrasted with their sibs mated at a later age, early-pregnant females from each line exhibited a decline in one or more component of reproductive performance, suggesting that the physiological state of the very young female was not optimum for normal pregnancy. In comparisons of early and later mating ages, all three lines showed a decreased littering rate at first mating, number born alive, and individual birth weight of progeny adjusted for litter size; L⁺ and L⁺W^– mice showed an increased perinatal mortality rate; L⁺ and L^–W⁺ had a reduction in litter size at birth. When the L⁺, L⁺W^– and L^–W⁺ lines were compared with an unselected strain and a line selected for high postweaning gain in similar experiments, a genotype by environment interaction was apparent since all lines did not respond in a similar manner to early mating. The line ranking for litter size at birth for each age at male-exposure was L⁺>L⁺W^–>L^–W⁺, despite the significant line by age interaction. When litter size was adjusted by covariance for body weight at mating, the significant effects of age at male-exposure and line by age interaction were eliminated. All fertile females were remated after they had weaned their first litter to obtain information on litter size in parity two. Line differences in litter size at birth and number born alive were uniform across parities. An age by parity interaction was evident since the decreased fecundity at younger ages of male exposure in the L⁺ and L^–W⁺ litters of parity one was not evident in parity two. Litter feed efficiency during first parity gestation was defined as litter birth weight divided by either cumulative feed intake of the dam from mating to parturition (GEI) or cumulative feed intake from weaning to parturition (GEII). The ranking of lines for GEI and GEH was L⁺> L⁺W^–>L^–W⁺, but when feed efficiency was adjusted for littering rate, L⁺W^– and L^–W⁺ were not significantly different. With regard to age at mating, the ranking for GEI (7 wk > 5 wk > 3 wk) was reversed from GEII (3 wk >5 wk > 7 wk) and these significant differences were maintained after adjustment for littering rate.Paper No. 6302 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentionedOn leave at the Institute of Animal Genetics, West Mains Road, Edinburgh EH9 3JN, Scotland. Supported, in part, by an Underwood Fund Fellowship, Agricultural Research Council, and an Edinburgh University Biological Fellowship in the Department of Genetics     

Heterosis in crosses between lines of Drosophila melanogaster selected for adaptation to different environments

Summary Experiments were designed to examine whether heterosis would occur in crosses of Drosophila melanogaster populations adapted to 18 °C or 28 °C environments. Crosses were examined in parental environments, an intermediate environment (23 °C) and a mixed environment (alternating 18°/28°C). Parental populations did not show divergence for larval viability, cold shock or high temperature mortalities when tested in a common environment. However, the 28 °C population was less fecund than the 18 °C population, but had higher larval competitive ability and higher adult longevity. Heterosis for viability, cold shock mortality and high temperature mortality occurred in crosses between a population adapted to 18 °C and another adapted to 28 °C, but not in crosses between two populations adapted to the same temperature. The results suggest that, in the absence of drift, heterosis is expected in crosses between lines or populations with different histories of selection but not between lines with the same selection histories.     

Distinct ethanol drinking microstructures in two replicate lines of mice selected for drinking to intoxication

The High Drinking in the Dark (HDID) mice have been selectively bred for reaching high blood ethanol concentrations (BECs) following the limited access Drinking in the Dark (DID) test. We have shown previously that mice from the first HDID replicate line (HDID‐1) drink in larger, but not longer, ethanol drinking bouts than the low‐drinking HS/Npt control mice when consuming modest amounts in the DID test. Here, we assessed drinking microstructure in HDID‐1 mice during binge‐like levels of ethanol intake using a lickometer system. Mice from both HDID replicates (HDID‐1 and ‐2) and HS mice were also given three DID tests (single‐bottle ethanol, two‐bottle choice and single‐bottle saccharin) using a continuously recording BioDAQ system to determine whether there are selection‐dependent changes in drinking microstructure. Larger ethanol bout size in the HDID‐1 mice than the HS mice was found to be due to a larger lick volume in these mice. HDID‐1 and HDID‐2 mice were also seen to have different drinking microstructures that both resulted in high intake and high BECs. The HDID‐1 mice drank in larger ethanol bouts than HS, whereas HDID‐2 mice drank in more frequent bouts. This pattern was also seen in two‐bottle choice DID. The HDID‐2 mice had a high bout frequency for all fluid types tested, whereas the large bout size phenotype of the HDID‐1 mice was specific to alcohol. These findings suggest that selection for drinking to intoxication has resulted in two distinct drinking microstructures, both of which lead to high BECs and high ethanol intake.