L. Bünger

Prediction of sensory characteristics of lamb meat samples by near infrared reflectance spectroscopy

This study was implemented to evaluate the potential of visible and near infrared reflectance (NIR) spectroscopy to predict sensory characteristics related to the eating quality of lamb meat samples. A total of 232 muscle samples from Texel and Scottish Blackface lambs was analyzed by chemical procedures and scored by assessors in a taste panel (TP). Then, these parameters were predicted from Vis/NIR spectra. The prediction equations showed that the absorbance data could explain a significant but relatively low proportion of the variability (R(2)<0.40) in the taste panel traits (texture, juiciness, flavour, abnormal flavour and overall liking) of the lamb meat samples. However, a top-tail approach, looking at the spectra of the 25 best and worst samples as judged by TP assessors, provided more meaningful results. This approach suggests that the assessors and the spectrophotometer were able to discriminate between the most extreme samples. This may have practical implications for sorting meat into a high quality class, which could be branded, into a low quality class sold for a lower price for less demanding food use. Regarding the chemical parameters, both intramuscular fat and water could be more accurately predicted by Vis/NIR spectra (R(2)=0.841 and 0.674, respectively) than sensory characteristics. In addition, the results obtained in the present study suggest that the more important regions of the spectra to estimate the sensory characteristics are related to the absorbance of these two chemical components in meat samples.

Mapping of obesity QTLs in a cross between mouse lines divergently selected on fat content.

Abstract. A genome-wide quantitative trait locus (QTL) analysis was performed in a polygenic obesity mouse model resulting from a long-term selection experiment. The parental lines were outbred lines divergently selected for 53 generations for high-fat (fat, F line) or low-fat (lean, L line) percentage (fat%) that differed fivefold in fat% at 14 weeks of age. An F2 population of 436 mice was used for the QTL analysis with 71 markers distributed across the genome. The analysis revealed significant QTLs Fob1 (for F-line obesity QTL 1), Fob2, Fob3, and Fob4, on Chromosomes (Chrs) 2, 12, 15, and X, respectively. None of these QTLs map to regions of known single gene obesity mutations (Lepob, Leprdb, Cpefat, Ay, tub), though they map to regions of previously described obesity QTLs and candidate genes. The effects of Fob1, Fob3, Fob4 were additive, and that of Fob2 was dominant. Fob2 also showed a significant female-specific effect. Fob1, Fob2, Fob3, and Fob4 explained 4.9%, 19.5%, 14.4%, and 7.3% of the F2 phenotypic variance for fat%, respectively. This study identified four loci that contributed to the response to divergent selection and control a significant proportion of the difference in obesity between the F and L lines.

A genetic investigation of various growth models to describe growth of lambs of two contrasting breeds

This study compared the use of various models to describe growth in lambs of 2 contrasting breeds from birth to slaughter. Live BW records (n = 7559) from 240 Texel and 231 Scottish Blackface (SBF) lambs weighed at 2-wk intervals were modeled. Biologically relevant variables were estimated for each lamb from modified versions of the logistic, Gompertz, Richards, and exponential models, and from linear regression. In both breeds, all nonlinear models fitted the data well, with an average coefficient of determination (R2) of > 0.98. The linear model had a lower average R2 than any of the nonlinear models (< 0.94). The variables used to describe the best 3 models (logistic, Gompertz, and Richards) included estimated final BW (A); maximum ADG (B); age at maximum ADG (C); position of point of inflection in relation to A (D, for Richards only). The Richards and Gompertz models provided the best fit (average R2 = 0.986 to 0.989) in both breeds. Richards estimated an extra variable, allowing increased flexibility in describing individual growth patterns, but the Akaikes information criteria value (which weighs log-likelihood by number of parameters estimated) was similar to that of the Gompertz model. Variables A, B, C, and D were moderately to highly heritable in Texel lambs (h2 = 0.33 to 0.87), and genetic correlations between variables within-model ranged from -0.80 to 0.89, suggesting some flexibility to change the shape of the growth curve when selecting for different variables. In SBF lambs, only variables from the logistic and Gompertz models had moderate heritabilities (0.17 to 0.56), but with high genetic correlations between variables within each model (< -0.88 or > 0.92). Selection on growth variables seems promising (in Texel more than SBF), but high genetic correlations between variables may restrict the possibilities to change the growth curve shape. A random regression model was also fitted to the data to allow predictions of growth rates at relevant time points. Heritabilities for growth rates differed markedly at various stages of growth and between the 2 breeds (Texel: 0.14 to 0.74; SBF: 0.07 to 0.34), with negative correlations between growth rate at 60 d of age and growth rate at finishing. Following these results, future studies should investigate genetic relationships between relevant growth curve variables and other important production traits, such as carcass composition and meat quality.

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

Abstract. 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.

Effects of the compact mutant myostatin allele Mstn (Cmpt-dl1Abc) introgressed into a high growth mouse line on skeletal muscle cellularity.

The murine myostatin mutation MstnCmpt-dl1Abc (Compact; C) was introduced into an inbred mouse line with extreme growth (DUHi) by marker-assisted introgression. To study the allelic effects on muscle fibre hyperplasia and hypertrophy, myonuclear proliferation, protein accretion, capillary density, and muscle fibre metabolism, samples from M. rectus femoris (RF) and M. longissimus dorsi (LD) muscles of animals wild-type (+/+), heterozygous (C/+), and homozygous (C/C) for the MstnCmpt-dl1Abc allele were examined by histological and biochemical analyses. Homozygous C/C mice exhibited lower body (−12%) but higher muscle weights (+38%) than ++ mice. Total muscle fibre number was increased (+24%), whereas fibre size was not significantly affected. Protein and DNA concentrations and DNA:protein ratios as well as specific CK activity remained unchanged for higher mass muscle implying increases in the total contents of DNA and muscle specific protein. Fibre type distribution was markedly shifted to the white glycolytic muscle fibres (+16–17% units) at the expense of red oxidative fibres. Capillary density was substantially lower in C/C than in ++ mice as seen by lower number of capillaries per fibre (−35%) and larger fibre area per capillary (+77%). However, the MstnCmpt-dl1Abc allele was partially recessive in heterozyogous C/+ mice for both fibre type frequencies and capillary density. The results show that hypermuscularity caused by mutations in the myostatin gene results from muscle fibre hyperplasia rather than hypertrophy, and from balanced increases in myonuclear proliferation and protein accretion. However, capillary supply is adversely affected and muscle metabolism shifted towards glycolysis, which could have negative consequences for physical fitness.

Evaluation of Video Image Analysis (VIA) technology to predict meat yield of sheep carcasses on-line under UK abattoir conditions.

The Meat and Livestock Commissions (MLC) EUROP classification based scheme and Video Image Analysis (VIA) system were compared in their ability to predict weights of primal carcass joints. A total of 443 commercial lamb carcasses under 12 months of age and mixed gender were selected by their cold carcass weight (CCW), conformation and fat scores. Lamb carcasses were classified for conformation and fatness, scanned by the VIA system and dissected into primal joints of leg, chump, loin, breast and shoulder. After adjustment for CCW, the estimation of primal joints using MLC EUROP scores showed high coefficients of determination (R(2)) in the range of 0.82-0.99. The use of VIA always resulted in equal or higher R(2). The precision measured as root mean square error (RMSE) was 27% (leg), 13% (chump), 1% (loin), 11% (breast), 5% (shoulders) and 13% (total primals) higher using VIA than MLC carcass information. Adjustment for slaughter day and gender effects indicated that estimations of primal joints using MLC EUROP scores were more sensitive to these factors than using VIA. This was consistent with an increase in stability of the prediction model of 28%, 11%, 2%, 12%, 6% and 14% for leg, chump, loin, breast and shoulder and total primals, respectively, using VIA compared to MLC EUROP scores. Consequently, VIA was capable of improving the prediction of primal meat yields compared to the current MLC EUROP carcass classification scheme used in the UK abattoirs.

INBRED LINES OF MICE DERIVED FROM LONG-TERM DIVERGENT SELECTION ON FAT CONTENT AND BODY WEIGHT

For identification of the genetic and physiological basis of growth and fatness, the establishment of inbred lines derived from divergently selected lines is an important tool (Lander and Botstein 1989; Festing 1997). It is necessary, first, to develop highly divergent selection lines for the traits of interest, and then to derive inbred lines from them. In this paper the origins and characteristics are described of two pairs of such inbreds derived from long-term selected lines for high and low body weight and fatness. The primary aim of selection experiments in mice is to increase the understanding of the genetics of quantitative traits. Once the divergence between selected lines is of sufficient magnitude, however, they become a valuable resource for studies in other disciplines of biology. Selection lines can be used to investigate underlying physiological or behavioral changes and to elucidate which components have changed and contributed to the observed selection response. Such investigations can focus on all levels of the organism—gene, hormones, enzymes, cell, tissue, organ, whole animal. For example, body weights and body composition have been extensively studied in mice as model mammalian quantitative traits (for example, Eisen 1989; Falconer 1992). However, the number, location, and effects of individual genes contributing to variation in those traits are mostly unknown. A primary goal of QTL mapping studies is to identify these genes (Falconer and Mackay 1996; Lynch and Walsh 1998). Some of the variation in general growth is caused by genes with major effects. A few mutations (hg, lit, dw, dw, pg, cmpt) have been found in mice that have major effects on growth altering the growth process in different ways and to different degrees. Whereas the hg mutation can increase weight gain (from 21 to 42 days) by 30–50%, other mutations decrease body weight by up to 75%. A dependence of gene effects on the genetic background can be expected, but has not yet been well investigated. Some of the variation in fat aggregation is caused by genes with major effects (for example, Fisler and Warden 1997; Pomp 1997). Five single gene mutations of major effects at fatness-related loci have been mapped in mice (A locus with two alleles A and A, Cpe, Tub, Lep, Lepr), altering fatness in different ways. The resulting obesity differs in extent, age of onset, and progression to obesity, and depends on genetic background. In some cases, excessive deposition of adipose tissue can lead to a twofold increase of body weight (Nobentrauth et al. 1996). Body weight is a composite trait aggregating both fat and non-fat tissue. Some genes may affect only fat or lean, whereas others may affect both; thus, if body composition is unknown, it is difficult to disentangle the underlying genes. It is certainly an advantage to have lines differing in body weight but not in fat percentage, and to have lines differing in fat percentage but not in the underlying fat-free body mass. Derivation of (outbred) selection lines. Selection lines were initiated in this laboratory in Edinburgh from a 3-way cross (two inbred [CBA, JU] and one outbred line [CFLP]) base (Sharp et al. 1984). Lines (P, or protein lines) were divergently selected for 20 generations for high (EPH) and low (EPL) lean mass, estimated from an index of body weight and gonadal fat pad weight in males. In subsequent generations, the selection criterion was body weight in both sexes at 10 weeks of age. From the same base population, lines were selected for increased and decreased fat content, resulting in fat (EF) and lean (EL) lines, with selection for the first 20 generations based on the ratio of gonadal fat pad weight to body weight of 10-week-old males. Subsequently, selection was on dry matter content of males at 14 weeks, which is strongly correlated with fat content (Hastings and Hill 1989). For the first 20 generations, three replicates were maintained per line, after which they were crossed to form one replicate. Selection was suspended from generation 53 to 58 (EPH, EPL) or 59 (EF, EL), while all mouse stocks were transferred to a new mouse house by embryo transfer.

The use of various live animal measurements to predict carcass and meat quality in two divergent lamb breeds

Live weight, subjective scores of condition and conformation, live animal video image analysis (LVIA), ultrasound and X-ray computed tomography (CT) scanning were used to investigate the best method or combination of methods for predicting carcass and meat quality traits in live Texel and Scottish Blackface lambs. Predictors derived from CT alone accounted for a high proportion of the variance in dissected fat and muscle weight in Texel lambs (adjusted R(2)=∼0.8), as well as intra-muscular fat content in the loin (∼0.6), but lower proportions in Blackface lambs (∼0.7 for fat, 0.4-0.5 for muscle and intra-muscular fat), after adjusting for sire and fixed effects. Adding traits measured by other in vivo methods increased prediction accuracies (adjusted R(2)) by up to 0.26, depending on trait and data set. Shear force and ultimate pH could not be accurately predicted using the traits considered here (adjusted R(2)<0.4). Although the same methods tended to be best for predicting product quality traits between breeds, prediction accuracies differed.

Thermoregulatory responses of two mouse Mus musculus strains selectively bred for high and low food intake

Abstract. We examined the thermoregulatory responses of male and female mice Mus musculus that had been divergently selected on voluntary food intake, corrected for body mass, to produce a high-intake and a low-intake strain. Resting metabolic rate was determined by indirect calorimetry (at 30°C, 25°C, 15°C and 5°C). Body temperature responses were measured in a separate group of mice in a parallel protocol. High-intake mice had significantly elevated body masses compared to low-intake mice in both sexes. Lower critical temperature in both strains appeared to be around 28°C. At 30°C there was a significant strain effect on resting metabolic rate, with high strain mice having greater metabolism than low strain mice. Sex and body mass were not significant main effects on resting metabolic rate and there were no significant interactions. Body temperature measured at 30°C, 25°C, 15°C and 5°C differed significantly between sexes (females higher) and there was a significant sex×body mass interaction effect, but there was no difference between strains. Thermal conductance was significantly related to strain and sex, mice from the high strain and males having greater thermal conductances than mice from the low strain and females. Artificial selection has resulted in high-intake mice having greater body masses and greater thermal conductances, which together account for up to 45% of the elevated daily energy demands that underpin the increase in food intake. The greater levels of food intake were also associated with higher resting metabolic rates at 30°C.

Analysis of response to 20 generations of selection for body composition in mice: fit to infinitesimal model assumptions

Data were analysed from a divergent selection experiment for an indicator of body composition in the mouse, the ratio of gonadal fat pad to body weight (GFPR). Lines were selected for 20 generations for fat (F), lean (L) or were unselected (C), with three replicates of each. Selection was within full-sib families, 16 families per replicate for the first seven generations, eight subsequently. At generation 20, GFPR in the F lines was twice and in the L lines half that of C. A log transformation removed both asymmetry of response and heterogeneity of variance among lines, and so was used throughout. Estimates of genetic variance and heritability (approximately 50%) obtained using REML with an animal model were very similar, whether estimated from the first few generations of selection, or from all 20 generations, or from late generations having fitted pedigree. The estimates were also similar when estimated from selected or control lines. Estimates from REML also agreed with estimates of realised heritability. The results all accord with expectations under the infinitesimal model, despite the four-fold changes in mean. Relaxed selection lines, derived from generation 20, showed little regression in fatness after 40 generations without selection.