Random-bred Controls Research Articles

Selection for longer limbs in mice increases bone stiffness and brittleness, but does not alter bending strength.

The ability of a bone to withstand loads depends on its structural and material properties. These tend to differ among species with different modes of locomotion, reflecting their unique loading patterns. The evolution of derived limb morphologies, such as the long limbs associated with jumping, may compromise overall bone strength. We evaluated bone mechanical properties in the Longshanks mouse, which was selectively bred for increased tibia length relative to body mass. We combined analyses of 3D shape and cross-sectional geometry of the tibia, with mechanical testing and bone composition assays, to compare bone strength, elastic properties and mineral composition in Longshanks mice and randomly bred controls. Our data show that, despite being more slender, cortical geometry and predicted bending strength of the Longshanks tibia were similar to controls. In whole bone bending tests, measures of bone bending strength were similar across groups; however, Longshanks tibiae were significantly more rigid, more brittle, and required less than half the energy to fracture. Tissue-level elastic properties were also altered in Longshanks mice, but the bones did not differ from the control in water content, ash content or density. These results indicate that while Longshanks bones are as strong as control tibiae, selection for increased tibia length has altered its elastic properties, possibly through changes in organic bony matrix composition. We conclude that selection for certain limb morphologies, and/or selection for rapid skeletal growth, can lead to tissue-level changes that can increase the risk of skeletal fracture, which in turn may favor the correlated evolution of compensatory mechanisms to mitigate increased fracture risk, such as delayed skeletal maturity.

Effects of genomic selection for intramuscular fat content in breast muscle in Chinese local chickens.

Improvements in living standards have resulted in consumers having higher expectations for chicken meat quality. This is particularly true in Asia, where there is high consumer preference for local breeds. Nothing is presently known about the effectiveness of using genomic selection (GS) strategies in chickens to genetically improve meat quality traits that cannot be measured in living potential parents. In this study, 724 Beijing-You chickens were used as a training population; all were genotyped using Illumina 60K SNP chips, and intramuscular fat content in breast muscle (IMFbr ) was measured. Birds in the GS line were selected based on genomic estimated breeding values, IMFbr being the sole trait. Genetic progress in one generation was compared to that from conventional family-based selection, and both were evaluated against random-bred controls. Results showed that relative to the random-bred controls, IMF percentage was improved 9.62% using GS, comparable to the 10.38% improvement using family-based selection. We quantified the effectiveness of GS when applied to a meat quality trait with low heritability in chickens. We plan to introduce custom SNP chips, appropriate for native chicken breeds in China, to assist in applying GS in local breeding and accelerate genetic gain.

Different Selection Strategies for the Improvement of the Growth Performance and Carcass Traits of Japanese Quails

ABSTRACT The present study evaluated different selection strategies to improve the growth performance and carcass traits of Japanese quails. To this end, 540 Japanese quails previously selected for high body weight at three ages (10, 12 and 14 weeks) from four close-bred flocks (Major, Kaleem, Saadat and Zahid) were subjected to three selection strategies: pedigree-based, mass selection or random-bred (controls). For pedigree-based selection, 108 birds (4 close-bred flocks × 3 age groups × 9 replicates × 1 bird each) with full pedigree and selected for high body weight were used, whereas in mass selection 324 birds (4 close-bred flocks × 3 age groups × 9 replicates × 3 birds each) with high body weight were selected to be the parents of next generation. Random-bred controls included 108 birds (4 close-bred flocks × 3 age groups × 9 replicates × 1bird each) which were not previously submitted to selection. The effects of selection strategies of Japanese quail parents from four close-bred flocks (CBF) at three ages on the performance growth and carcass traits of their progenies were measured. The parent flocks were selected at three ages (10, 12 and 14 weeks) and reared for 20 weeks, and their progenies were reared for four weeks. The progeny of pedigree-based selected parents presented better feed intake (g), body weight gain (g), feed conversion ratio, live and carcass weights (g), and carcass yield. The progeny of 10- and 14-week-old parents showed better growth performance and carcass traits, respectively. Moreover, there was no influence of CBF on growth and carcass traits. It was concluded that pedigree-based selection had pronounced effect on the growth performance and carcass traits of the progeny compared with mass selection and random breeding. It is suggested that parental ages of 10 and 14 weeks of age promote better progeny growth performance and carcass traits.

Artificial selection sheds light on developmental mechanisms of limb elongation.

Species diversity in limb lengths and proportions is thought to have evolved adaptively in the context of locomotor and habitat specialization, but the heritable cellular processes that drove this evolution within species are poorly understood. In this study, we take a novel "micro-evo-devo" approach, using artificial selection on relative limb length to amplify phenotypic variation in a population of mice, known as Longshanks, to examine the cellular mechanisms of postnatal limb development that contribute to intraspecific limb length variation. Cross-sectional growth data indicate that differences in bone length between Longshanks and random-bred controls are not due to prolonged growth, but to accelerated growth rates. Histomorphometric and cell proliferation assays on proximal tibial growth plates show that Longshanks' increased limb bone length is associated with an increased number of proliferative chondrocytes. In contrast, we find no differences in other growth plate cellular features known to underlie interspecific differences in limb bone size and shape, such as the rates of chondrocyte proliferation or the size and number of hypertrophic cells in the growth plate. These data suggest that small differences among individuals in the number of proliferating chondrocytes are a potentially important determinant of selectable intraspecific variation in individual limb bone lengths, independent of body size.

Enhanced limbic/impaired cortical-loop connection onto the hippocampus of NHE rats: Application of resting-state functional connectivity in a preclinical ADHD model

Due to a hyperfunctioning mesocorticolimbic system, Naples-High-Excitability (NHE) rats have been proposed to model for the meso-cortical variant of attention deficit/hyperactivity disorder (ADHD). Compared to Naples Random-Bred (NRB) controls, NHE rats show hyperactivity, impaired non-selective attention (Aspide et al., 1998), and impaired selective spatial attention (Ruocco et al., 2009a, 2014). Alteration in limbic functions has been proposed; however, resulting unbalance among forebrain areas has not been assessed yet. By resting-state functional Magnetic-Resonance Imaging (fMRI) in vivo, we investigated the connectivity of neuronal networks belonging to limbic vs. cortical loops in NHE and NRB rats (n=10 each). Notably, resting-state fMRI was applied using a multi-slice sagittal, gradient-echo sequence. Voxel-wise connectivity maps at rest, based on temporal correlation among fMRI time-series, were computed by seeding the hippocampus (Hip), nucleus accumbens (NAcc), dorsal striatum (dStr), amygdala (Amy) and dorsal/medial prefrontal cortex (PFC), both hemispheres. To summarize patterns of altered connection, clearly directional connectivity was evident within the cortical loop: bilaterally and specularly, from orbital and dorsal PFCs through dStr and hence towards Hip. Such network communication was reduced in NHE rats (also, with less mesencephalic/pontine innervation). Conversely, enhanced network activity emerged within the limbic loop of NHE rats: from left PFC, both through the NAcc and directly, to the Hip (all of which received greater ventral tegmental innervation, likely dopamine). Together with tuned-down cortical loop, this potentiated limbic loop may serve a major role in controlling ADHD-like behavioral symptoms in NHE rats.

Immunization with DISC1 protein in an animal model of ADHD influences behavior and excitatory amino acids in prefrontal cortex and striatum.

The Disrupted-in-schizophrenia 1 (DISC1) gene is involved in vulnerability to neuropsychiatric disorders. Naples high-excitability (NHE) rat model neuropsychiatric problems characterized by an unbalanced mesocortical dopamine system. Here, we assessed behavioral and neurochemical effects of immunization against multimeric rat DISC1 protein in adult NHE rats, an animal model of attention-deficit hyperactivity disorder and their Random-Bred (NRB) controls. Males of both lines received subcutaneous injections of vehicle (PB), adjuvant only (AD) or recombinant rat DISC1 protein purified from E. coli, suspended in AD (anti-DISC1) at age of 30, 45 and 60 postnatal days (pnd). At 75 pnd, the rats were exposed to a Làt maze and 2days later to an Olton eight-arm radial maze, and horizontal (HA) and vertical activities (VA) were monitored. Non-selective (NSA) and selective spatial attention (SSA) were monitored in the Làt and in the Olton maze by duration of rearings and working memory, respectively. Post mortem neurochemistry in the prefrontal cortex (PFc), dorsal (DS) and ventral (VS) striatum of L-Glutamate, L-Aspartate and L-Leucine was performed. All immunized rats showed a clear humoral IgM (but not IgG) immune response against the immunogen, indicating that immunological self-tolerance to DISC1 can be overcome by immunization. NHE rats exhibited a higher unspecific IgM response to adjuvant, indicating an immunological abnormality. The sole anti-DISC1 immunization-specific behavioral in the NHE rats was an increased horizontal activity in the Làt maze. Adjuvant treatment increased vertical activity in both lines, but in the NRB controls it increased rearing and decreased horizontal activity. Liquid chromatography/tandem mass spectrometry analysis of soluble or membrane-trapped neurotransmitters aspartate, glutamate and leucine revealed increased soluble aspartate levels in the ventral striatum of NRB controls after anti-DISC1 immunization. Immune activation by adjuvant independent of simultaneous DISC1 immunization led to other specific changes in NHE and control NRB rats. In DISC1-immunized NHE rats, horizontal activity in Lat maze correlated with membrane-trapped glutamate in PFc and in the NRB rats, duration of rearing in Olton maze correlated with membrane-trapped glutamate in PFc and aspartate in dorsal striatum. In addition to non-specific immune activation (by AD), the postnatal anti-DISC1 immune treatment led to behavioral changes related to mechanisms of activity and attention and had influenced amino acids and synaptic markers in striatum and neocortex in the adult NHE as well as control animals.

Impacts of genetic correlation on the independent evolution of body mass and skeletal size in mammals.

BackgroundMammals show a predictable scaling relationship between limb bone size and body mass. This relationship has a genetic basis which likely evolved via natural selection, but it is unclear how much the genetic correlation between these traits in turn impacts their capacity to evolve independently. We selectively bred laboratory mice for increases in tibia length independent of body mass, to test the hypothesis that a genetic correlation with body mass constrains evolutionary change in tibia length.ResultsOver 14 generations, we produced mean tibia length increases of 9-13%, while mean body mass was unchanged, in selectively bred mice and random-bred controls. Using evolutionary scenarios with different selection and quantitative genetic parameters, we also found that this genetic correlation impedes the rate of evolutionary change in both traits, slowing increases in tibia length while preventing decreases in body mass, despite the latter’s negative effect on fitness.ConclusionsOverall, results from this ongoing selection experiment suggest that parallel evolution of relatively longer hind limbs among rodents, for example in the context of strong competition for resources and niche partitioning in heterogeneous environments, may have occurred very rapidly on geological timescales, in spite of a moderately strong genetic correlation between tibia length and body mass.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0258-0) contains supplementary material, which is available to authorized users.

Impacts of genetic correlation on the independent evolution of body mass and skeletal size in mammals

Mammals show a predictable scaling relationship between limb bone size and body mass. This relationship has a genetic basis which likely evolved via natural selection, but it is unclear how much the genetic correlation between these traits in turn impacts their capacity to evolve independently. We selectively bred laboratory mice for increases in tibia length independent of body mass, to test the hypothesis that a genetic correlation with body mass constrains evolutionary change in tibia length. Over 14 generations, we produced mean tibia length increases of 9-13%, while mean body mass was unchanged, in selectively bred mice and random-bred controls. Using evolutionary scenarios with different selection and quantitative genetic parameters, we also found that this genetic correlation impedes the rate of evolutionary change in both traits, slowing increases in tibia length while preventing decreases in body mass, despite the latter’s negative effect on fitness. Overall, results from this ongoing selection experiment suggest that parallel evolution of relatively longer hind limbs among rodents, for example in the context of strong competition for resources and niche partitioning in heterogeneous environments, may have occurred very rapidly on geological timescales, in spite of a moderately strong genetic correlation between tibia length and body mass.

Growth, carcase and meat traits and gene expression in chickens divergently selected for intramuscular fat content

1. Changes resulting from divergent selection after 5 generations for intramuscular fat (IMF) content in breast muscle in a population of purebred Beijing-You chickens were investigated. Female chickens from lines selected-up (UL) and selected-down (DL) for 5 generations and random-bred controls (CL) were studied at 120 d of age.2. In the UL, IMF in breast muscle (4.65%) was 1.38 times that in the DL (3.36%). The IMF content in leg muscle was also higher in UL compared to DL.3. There were significant differences in growth, carcase traits and meat quality between the two selected lines. However, ultimate pH (pHu) was lower and lightness (L*) and yellowness (b*) were higher in breast muscles of UL birds compared to DL birds. Similar trends for pHu and L* value between UL and DL were observed in leg muscle.4. Significant mRNA expression differences of the heart fatty acid-binding protein (H-FABP) gene between UL and DL were observed in breast muscle, and a negative correlation between expression of mRNA and IMF% in breast and leg muscles pointed to H-FABP as a potential selection candidate gene.

Excitatory amino acids in the forebrain of the Naples high-excitability rats: neurochemical and behavioural effects of subchronic d-aspartate and its diethyl ester prodrug

The excitatory amino acids (EAA) l-glutamate ( l-Glu), l-aspartate ( l-Asp) and d-aspartate ( d-Asp) are thought to play a neurotransmitter/neuromodulator role in neuronal communications. Recently, a high level of EAA l-Glu, d- and l-Asp isomers has been found in the forebrain of Naples high-excitability (NHE) rat line that models the mesocortical variant of Attention-Deficit Hyperactivity Disorder (ADHD). The aim of this study was to assess the functions of d-Asp using two forms, i.e. free d-Asp or d-Asp diethyl ester (DEE) as prodrug, on brain and behaviour. Thus, prepuberal rats were given, for two weeks daily, an i.p. injection of d-Asp or DEE or vehicle. Then rats were exposed to two spatial novelties i.e. Làt and radial Olton maze. Behaviour was monitored for indices of activity, non-selective attention (NSA), selective spatial attention (SSA) and emotional reactivity. l-Glu and d- and l-Asp were detected by HPLC in cognitive and non-cognitive brain areas such as prefrontal cortex, striatum, hippocampus and hypothalamus. Results indicate that subchronic d-Asp or DEE (i) reduced EAA levels in the NHE and increased it in the random-bred controls (NRB) rats, (ii) in the Làt-maze d-Asp increased horizontal activity in NHE but DEE decreased it in NRB rats, (iii) in the Olton maze d-Asp and DEE decreased vertical activity in NHE and NRB rats respectively, (iv) d-Asp impaired attention only in NRB decreasing number of arms visited before first repetition. Therefore, data demonstrate differential effects of prepuberal subchronic d-Asp and DEE that may be related to different basal EAA levels in NHE and NRB rats.

Protein Synthesis and Antioxidant Capacity in Aging Mice: Effects of Long‐Term Voluntary Exercise

Exercise increases metabolic rate and the production of reactive oxygen species (ROS) but also elevates protein turnover. ROS cause damage to macromolecules (e.g., proteins) and thereby contribute to aging. Protein turnover removes and replaces damaged proteins. The balance between these two responses may underlie beneficial effects of physical activity on aging. Effects of lifelong exercise on antioxidant enzyme activities and fractional synthesis rate of protein (FSRP) were examined at various ages (2-26 mo) in heart, liver, and muscle of mice that had been selectively bred for high wheel-running activity, housed with (S+) or without (S-) a running wheel, and their random-bred controls (C+) housed with running wheels. FSRP decreased with age and increased in muscle of young, but not old, activity-selected mice. Enzyme activity of superoxide dismutase and glutathione peroxidase decreased with age and showed a peak at 10 mo of age in liver. Selection for wheel-running activity did not affect antioxidant enzyme activity. Daily energy expenditure correlated positively with antioxidant levels in liver. This might indicate that oxidative stress (ROS production) increases with metabolic rate, driving upregulation of antioxidant enzymes. Alternatively, the elevated energy expenditure may reflect the energetic cost of elevated protection, consistent with the disposable-soma hypothesis and with other studies showing positive links between energy expenditure and life span. Long-term elevations in voluntary exercise did not result in elevations in antioxidant enzyme activities or protein synthesis rates.

Dam Line and Sire Line Effects on Turkey Embryo Survival and Thyroid Hormone Concentrations at the Plateau Stage in Oxygen Consumption

Inheritance of embryo thyroid function was measured in lines of turkeys. Two lines that had been selected for either increased egg production (E) or increased 16-wk BW (F) and their respective randombred controls (i.e., RBC1 and RBC2) were examined. Reciprocal crosses of dams and sires from each selected line and its randombred control were made to estimate sire line and dam line effects. Orthogonal contrasts were used to determine if the differences found were due to the presence of additive, nonadditive, or maternal, sex-linked, or both, gene effects. With the data involved, sex-linkage and maternal effects could not be separated. Embryo survival was measured for all lines and their reciprocal crosses. Crossing the RBC1 sire and E dam also resulted in better embryo survival and lower death losses at pipping than for the other cross- or purelines. Reciprocal crosses of the F and RBC2 lines showed better total embryo survival, and they survived pipping better than the F or RBC2 purelines. Thyroxine (T4) and triiodothyronine (T3) concentrations differed between the reciprocal crosses at external pipping, but the effects were inconsistent for the 2 data sets. Reciprocal tests indicated that maternal, sex-linked, or both, effects were present for T3 concentrations at internal pipping in the E and RBC1 lines and at external pipping for the F and RBC2 lines. Reciprocal effects were significant for T4 at internal pipping for both data sets. The RBC1 sire embryos had significantly higher T3:T4 ratios than the E line sire embryos at internal and external pipping, and the pureline RBC1 embryos had consistently higher ratios than the pureline E embryos. The differences for the T3:T4 ratios between these 2 lines at internal pipping, external pipping, and hatch appeared to be consistently additive in nature, although significant nonadditive or heterotic effects were present for the ratio at external pipping. Similar effects on the T3:T4 ratio were observed for the F and RBC2 lines at external pipping.

Genetic Control of Neonatal Growth and Intestinal Maturation in Turkeys

Turkey experimental lines E (selected 44 yr for increased egg production) and F (selected 38 yr for increased 16-wk BW) were mated reciprocally with the randombred control lines from which they were derived (RBC1 and RBC2, respectively), and the pure line and reciprocal cross poults were compared according to their hatch, 3- and 7-d BW, jejunum weight, jejunum length, and jejunal maltase and alkaline phosphatase activities. Orthogonal contrasts of the data from the pure line and reciprocal cross-poult data were used to estimate additive genetic effects, reciprocal effects (confounded maternal and sex-linked effects), and heterosis for each of the traits measured. Body weights at hatch and at 3 and 7 d of age were increased in the F line relative to the RBC2 line and were decreased in the E line relative to the RBC1 line. The genetic changes from long-term selection in the E and F lines have had concomitant effects on jejunum growth and function that parallel the changes in growth rate. The increased BW of the F line poults and the decreased BW of the E line poults relative to their randombred controls may be due to increases in the absorption of nutrients because of greater intestinal mass rather than to differences in glucose digestion. Concomitant changes in egg weight in the 2 selected lines appear to have resulted in maternal effects that have significantly affected neonatal BW and digestive system maturation.

Wheel-running activity and energy metabolism in relation to ambient temperature in mice selected for high wheel-running activity

Interrelationships between ambient temperature, activity, and energy metabolism were explored in mice that had been selectively bred for high spontaneous wheel-running activity and their random-bred controls. Animals were exposed to three different ambient temperatures (10, 20 and 30 degrees C) and wheel-running activity and metabolic rate were measured simultaneously. Wheel-running activity was decreased at low ambient temperatures in all animals and was increased in selected animals compared to controls at 20 and 30 degrees C. Resting metabolic rate (RMR) and daily energy expenditure (DEE) decreased with increasing ambient temperature. RMR did not differ between control and selected mice, but mass-specific DEE was increased in selected mice. The cost of activity (measured as the slope of the relationship between metabolic rate and running speed) was similar at all ambient temperatures and in control and selected mice. Heat generated by running apparently did not substitute for heat necessary for thermoregulation. The overall estimate of running costs was 1.2 kJ/km for control mice and selected mice.

Effects of Selection for Increased Body Weight, Egg Production, and Shank Width on Developmental Stability in Turkeys

Bilateral asymmetry was measured at 20 wk of age for shank length, shank width (width laterally at the dew claw), shank depth (width perpendicular to the dew claw), and face length (between auditory canal opening and the posterior junction of the upper and lower mandible) in three randombred control lines and three selected lines of turkeys. The data were based on 50 or 51 individuals per line and sex subgroup from a single hatch. The lines were grown intermingled with the sexes being grown in different houses. The selected lines had been selected for increased egg production (38 generations), increased 16-wk BW (32 generations), or increased shank width (19 generations) and had a higher level of inbreeding (average = 36.9%) than the randombred controls (RBC; average = 11.6%). The bilateral differences (right minus left) were analyzed for the presence of fluctuating asymmetry (FA; zero signed mean with normal variation), directional asymmetry (DA; signed mean not zero with normal variation), and antisymmetry (AS; zero mean with non-normal distribution). In order to adjust for possible scaling effects, relative asymmetry (RA), in which the mean of the absolute differences between sides was divided by the mean of the two sides and the resulting value was multiplied by 100, was used as a measure of bilateral asymmetry. The randombred control and selected lines were contrasted to study the effect of homozygosity on RA. Likewise, the large-bodied lines (F, FL, and RBC3) were contrasted to the small-bodied lines (RBC1, E, and RBC2) to study the effect of BW on RA.Only two types (FA and DA) of asymmetry were observed in the present study. The level of asymmetry for the traits was ranked as follows: face length > shank width = shank depth > shank length. The individual lines differed in RA for shank length and shank width for both sexes and for shank depth and face length in females. In general, the influence of BW, as measured in the contrast of large-bodied and small-bodied lines, on RA was larger than that of homozygosity, as measured by the contrast of the selected and randombred control lines.

Effect of supplemental oxygen on blood plasma organic acids within embryos from selected lines of turkeys

The hypothesis was tested that increased oxygen tensions during the plateau stage of oxygen consumption (25 and 26 d of incubation) would cause different metabolic responses from embryos selected for increased egg production or growth. Embryos were exposed to 171 or 152 mm Hg partial pressure of oxygen from 25 to 28 d of incubation, a time when the oxygen conductance properties of the eggshell are exceeded by the embryonic tissue demands for oxygen. Carbohydrate and lipid metabolism were observed by measuring plasma organic acids in embryos from selected lines and randombred controls. (E was selected for increased egg production; RBC1 is the randombred line from which it was selected. F was selected for increased BW; RBC2 is the randombred line from which it was selected.) During the plateau stage in oxygen consumption, RBC2 embryos responded to added oxygen by utilizing fat rather than carbohydrate, whereas F embryos responded by using less fat as well as less carbohydrate from the liver and kidney. The response of F embryos to added oxygen is the opposite that might be expected for aerobic metabolism. The reason that selection for growth has resulted in such a metabolism is unknown. The E embryos displayed depressed lactate and beta-hydroxybutyrate levels, but plasma urates were elevated compared with RBC1, suggesting that the selection for egg production has also resulted in a unique metabolism. The embryonic processes described in the current study suggest that selected embryos are unable to respond to elevated partial pressure of oxygen by adjusting energy metabolism, which may result in increased embryonic mortality during this stage.

Genetic relationship among lines and smooth muscle and ovarian follicular development within lines of Japanese quail in two long-term selection studies

Smooth muscle tumor and ovarian follicular development were studied in lines of Japanese quail selected for increased 4-wk BW (HW, P, and T) and their randombred controls (C and R1). The lines studied were from long-term selection studies at The Ohio State University (HW and R1) and The University of Georgia (P, T, and C). To study the genetic relationship among the lines in the two selection studies, the C, P, HW, and R1 lines were DNA-fingerprinted by digestion of the DNA with the HaeIII restriction enzyme and using Jeffreys' 33.6 probe. The BW of females at 4 wk of age and at the end of a 240-d egg production period were similar for the C and R1 lines. The BW of the selected lines was ranked P > T > HW for both measurements. Smooth muscle tumors were found in the oviducal ligaments adjacent to the magnum. A greater percentage of hens from the BW-selected lines had smooth muscle tumors of greater weight than the randombred control lines, which did not differ in tumor incidence or weight. The P and T lines had a greater incidence of multiple-lobed tumors than the HW line. Based on bandsharing (BS) of DNA fingerprints, the Georgia and Ohio lines did not appear to be closely related, suggesting that, perhaps, the smooth muscle tumors in the BW-selected lines in the two studies might have resulted from pleiotrophic effects of genes affecting growth or to genes closely linked to the growth genes. The BW-selected lines in both selection studies had more ovarian follicles in rapid development, which were of greater weight, than the randombred control lines. The HW line had a larger number of ovarian follicles in rapid development than the P and T lines. The percentage of hens with atretic follicles was greater in the BW-selected lines. The results of the present study suggest that the effect of BW selection on ovarian follicular development may occur early in selection (within the first 30 generations) and is not influenced by additional genetic changes in BW.

Effect of genetics and maternal dietary iodide supplementation on turkey embryonic growth

Embryonic growth of a turkey lines selected for 16-wk BW (F) or 180-d egg production (E) was measured and compared to randombred controls (RBC2 or RBC1). Egg weight at setting relative to poult weight at hatching indicated increased growth in F as well as E embryos compared to randombred controls. Eggs from F weighed 10 g more than those of RBC2 (P < or = 0.0001) but the poults at hatching were only 8 g heavier (P < or = 0.0001). Water vapor loss during incubation indicated that only 0.9% of the difference could be accounted for by water vapor loss. Selection for increased 16-wk BW resulted in decreased embryo growth rates relative to hatchling mass (P < or = 0.0001) beginning at Day 16 of incubation compared to that of RBC2. Eggs from E weighed 15 g less than RBC1 (P < or = 0.0001) but produced poults weighing only 7 g less (P < or = 0.0001). Incubation water vapor loss was depressed in E compared to RBC1 (P < or = 0.0001) but accounted for only 1.4% of the difference between hatchling weights. Selection for egg production increased embryo growth rates (relative to hatchling mass) measured at 4-d intervals compared to those of the RBC1 line (P < or = 0.05). Iodide supplementation of the maternal diet depressed (P < or = 0.05) glycogen in F embryos but interacted with line to generally increase glycogen in E embryos. Increased glycogen was related to increased growth rates in E but not F line embryos. It may be concluded that iodide supplementation of the material diet and genetics are determinants of embryonic growth in turkeys.

Altered growth of mice divergently selected for body weight is associated with complex changes in the growth hormone/insulin-like growth factor system

Mice investigated in this study were generated by selecting a sub-population of the NMRI out-bred stock (C), for high (H) or low (L) 8-week body weight. After 58 generations of selection, 8-week body weights of the sub-populations were markedly different if compared to controls. To investigate endocrine changes causing the altered growth performance in the different lines of mice, we analysed several components of the growth hormone (GH)/insulin-like growth factor (IGF) system. Pituitary weights of male and female L mice were significantly smaller than those of C and H mice. Relative to body weight, pituitary weights of male mice from the three lines did not differ, however pituitary weight-to-body weight-ratios of female L mice were significantly greater than those of H females. Mean volume densities of somatotropic cells were significantly smaller in L mice than in C and H mice. Serum IGF-I concentrations were significantly lower in the L line than in the C and H lines. H mice displayed significantly increased serum insulin levels both after ad libitum feeding and after a 14 hour fasting period. Ligand blot analysis of serum IGF-binding proteins (IGFBPs) revealed a significant reduction of circulating IGFBP-3 in L mice as compared to C and H mice. In contrast, serum IGFBP-2 mRNA levels were significantly increased in male L mice and showed non significant increases in female L mice. Hepatic IGFBP-2 mRNA levels were significantly increased in L mice and decreased in H mice as compared to C mice. Expression of IGFBP-4 mRNA in the liver was significantly decreased in both selection lines (L, H) as compared to the random-bred controls. Our findings demonstrate that altered growth of mice resulting from selection for body weight is associated with complex changes in the endocrine network of the GH/IGF system.

Intestinal dimensions of mice divergently selected for body weight.

Selection for body weight provides important animal models for studying mechanisms of growth regulation. This study evaluated growth responses of the gastrointestinal tract (GIT) to long-term selection of mice for high (H line) or low (L line) 8-week body weight as compared with random-bred controls (C line). Weights and dimensions of the various parts of the GIT were recorded from 8-month-old mice. For light microscopic stereological analyses, samples were taken from eight equidistant locations covering the whole jejunum/ileum. Vertical sections were used for estimation of fractional volumes of mucosa, submucosa, and muscularis and of villous surface area density and for measurement of villus length. Differences between groups in weights and dimensions of the various parts of the GIT were more pronounced in the proximal than in the distal segments, with greatest values in H, followed by C and L mice. Relative to body weight, intestinal growth was similar in the three lines, except for significantly (P < 0.001) increased relative weights of jejunum/ ileum, caecum, and colon in L mice. The fractional volume of mucosa and villus length decreased, whereas the fractional volumes of submucosa and muscularis increased from the proximal to the distal locations. The absolute volume of mucosa was greatest in H mice, followed by C and L mice. Relative to body weight, the volume of mucosa was significantly (P < 0.01) greater in L mice than in the two other lines. The mean total villous surface area of jejunum/ileum was significantly (P < 0.01) different among the three lines (L line: 144 cm2; C line: 227 cm2; H line: 304 cm2) but proportionate to differences in metabolic body weight. Selection for body weight affected various parts of the GIT to a different extent. The parameters investigated changed markedly along the small intestine, demonstrating the need for systematic sampling. Vertical section stereology provides unbiased estimates of total villous surface area, which is a parameter of major biological significance.