Genetic parameters associated with meat quality of Nellore cattle at different anatomical points of longissimus: Brazilian standards

The present study estimated genetic parameters and evaluated the genetic and phenotypic correlations between meat quality characteristics of Nellore cattle evaluated at different anatomical points of the longissimus. Data from 1329 Nellore young bulls were used to evaluate, in the 5th and 12th ribs, marbling score (MAR), shear force (SF), cooking weight losses (CWL) and intramuscular fat (IMF). In addition, the subcutaneous fat thickness was measured at the 12th rib (SFT₁₂) and between the last lumbar and the first sacral vertebrae (SFT_LR), in the separation of loin and round. Results yielded moderate heritability coefficients for evaluated characteristics, except CWL. High genetic correlations (0.61) were found between measurements of SFT₁₂ and SFT_LR. MAR, IMF and SF were evaluated at the 5th and 12th rib. Meat quality and subcutaneous fat thickness measured at different anatomical points of the longissimus are genetically correlated and can be used in genetic selection programs to improve meat quality characteristics in Nellore cattle.

Predicting the shear value and intramuscular fat in meat from Nellore cattle using Vis-NIR spectroscopy

Visible and near-infrared spectroscopy (Vis-NIRS) was tested for its effectiveness in predicting intramuscular fat (IMF) and WBSF in Nellore steers. Beef samples from longissimus thoracis, aged for either 2 or 7 days, had their spectra collected for wavelengths ranging from 400 to 1395 nm. Partial least squares regression models were developed for each trait. Determination coefficients of calibration models for WBSF ranged from 0.17 to 0.53. Considering WBSF in samples aged for 2 days, Vis-NIR correctly classified 100% of tough samples (>45 N), but wrongly classified all tender samples (≤45 N) as tough. Determination coefficients of calibration models for IMF ranged from 0.12 to 0.14. Vis-NIRS is a useful tool for identifying tough beef, but it is less effective in predicting tender samples and IMF. Additional studies are necessary to generate more robust models for the prediction of intramuscular fat in intact meat samples of Nellore cattle.

Oxidative costs of reproduction in mouse strains selected for different levels of food intake and which differ in reproductive performance

Oxidative damage caused by reactive oxygen species has been hypothesised to underpin the trade-off between reproduction and somatic maintenance, i.e., the life-history-oxidative stress theory. Previous tests of this hypothesis have proved equivocal, and it has been suggested that the variation in responses may be related to the tissues measured. Here, we measured oxidative damage (protein carbonyls, 8-OHdG) and antioxidant protection (enzymatic antioxidant activity and serum antioxidant capacity) in multiple tissues of reproductive (R) and non-reproductive (N) mice from two mouse strains selectively bred for high (H) or low (L) food intake, which differ in their reproductive performance, i.e., H mice have increased milk energy output (MEO) and wean larger pups. Levels of oxidative damage were unchanged (liver) or reduced (brain and serum) in R versus N mice, and no differences in multiple measures of oxidative protection were found between H and L mice in liver (except for Glutathione Peroxidase), brain or mammary glands. Also, there were no associations between an individual’s energetic investment (e.g., MEO) and most of the oxidative stress measures detected in various tissues. These data are inconsistent with the oxidative stress theory, but were more supportive of, but not completely consistent, with the ‘oxidative shielding’ hypothesis.

Myostatin dysfunction impairs force generation in extensor digitorum longus muscle and increases exercise-induced protein efflux from extensor digitorum longus and soleus muscles

Myostatin dysfunction promotes muscle hypertrophy, which can complicate assessment of muscle properties. We examined force generating capacity and creatine kinase (CK) efflux from skeletal muscles of young mice before they reach adult body and muscle size. Isolated soleus (SOL) and extensor digitorum longus (EDL) muscles of Berlin high (BEH) mice with dysfunctional myostatin, i.e., homozygous for inactivating myostatin mutation, and with a wild-type myostatin (BEH+/+) were studied. The muscles of BEH mice showed faster (P < 0.01) twitch and tetanus contraction times compared with BEH+/+ mice, but only EDL displayed lower (P < 0.05) specific force. SOL and EDL of age-matched but not younger BEH mice showed greater exercise-induced CK efflux compared with BEH+/+ mice. In summary, myostatin dysfunction leads to impairment in muscle force generating capacity in EDL and increases susceptibility of SOL and EDL to protein loss after exercise.

Effect of the Texel muscling QTL (TM-QTL) on spine characteristics in purebred Texel lambs

Previous work showed that the Texel muscling QTL (TM-QTL) results in pronounced hypertrophy in the loin muscle, with the largest phenotypic effects observed in lambs inheriting a single copy of the allele from the sire. As the loin runs parallel to the spinal vertebrae, and the development of muscle and bone are closely linked, the primary aim of this study was to investigate if there were any subsequent associations between TM-QTL inheritance and underlying spine characteristics (vertebrae number, VN; spine region length, SPL; average length of individual vertebrae, VL) of the thoracic, lumbar, and thoracolumbar spine regions. Spine characteristics were measured from X-ray computed tomography (CT) scans for 142 purebred Texel lambs which had been previously genotyped. Least-squares means were significantly different between genotype groups for lumbar and thoracic VN and lumbar SPL. Similarly for these traits, contrasts were shown to be significant for particular modes of gene action but overall were inconclusive. In general, the results showed little evidence that spine trait phenotypes were associated with differences in loin muscling associated with the different TM-QTL genotypes.

Limits to sustained energy intake. XXII. Reproductive performance of two selected mouse lines with different thermal conductance

Maximal sustained energy intake (SusEI) appears limited, but the factors imposing the limit are disputed. We studied reproductive performance in two lines of mice selected for high and low food intake (MH and ML, respectively), and known to have large differences in thermal conductance (29% higher in the MH line at 21°C). When these mice raised their natural litters, their metabolisable energy intake significantly increased over the first 13 days of lactation and then reached a plateau. At peak lactation, MH mice assimilated on average 45.3 % more energy than ML mice (222.9±7.1 and 153.4±12.5 kJ day-1, N=49 and 24, respectively). Moreover, MH mice exported on average 62.3 kJ day-1 more energy as milk than ML mice (118.9±5.3 and 56.6±5.4 kJ day-1, N= subset of 32 and 21, respectively). The elevated milk production of MH mice enabled them to wean litters (65.2±2.1 g) that were on average 50.2% heavier than litters produced by ML mothers (43.4±3.0 g), and pups that were on average 27.2% heavier (9.9±0.2 and 7.8±0.2 g, respectively). Lactating mice in both lines had significantly longer and heavier guts compared to non-reproductive mice. However, inconsistent with the central limit hypothesis, the ML mice had significantly longer and heavier intestines than MH mice. An experiment where the mice raised litters of the opposing line demonstrated that lactation performance was not limited by offspring growth capacity. Our findings are consistent with the idea that the SusEI at peak lactation is constrained by the capacity of the mothers to dissipate body heat.

Genetic and genomic analyses of musculoskeletal differences between BEH and BEL strains

Berlin high (BEH) and Berlin low (BEL) strains selected for divergent growth differ threefold in body weight. We aimed at examining muscle mass, which is a major contributor to body weight, by exploring morphological characteristics of the soleus muscle (fiber number and cross sectional area; CSA), by analyzing the transcriptome of the gastrocnemius and by initiating quantitative trait locus (QTL) mapping. BEH muscles were four to eight times larger than those of BEL. In substrain BEH+/+, mutant myostatin was replaced with a wild-type allele; however, BEH+/+muscles still were two to four times larger compared with BEL. BEH soleus muscle fibers were two times more numerous (P < 0.0001) and CSA was two times larger (P < 0.0001) compared with BEL. In addition, soleus femoral attachment anomaly (SFAA) was observed in all BEL mice. One significant (Chr 1) and four suggestive (Chr 3, 4, 6, and 9) muscle weight QTLs were mapped in a 21-day-old F2 intercross (n = 296) between BEH and BEL strains. The frequency of SFAA incidence in the F2 and in the backcross to BEL strain (BCL) suggested the presence of more than one causative gene. Two suggestive SFAA QTLs were mapped in BCL; however, their peak markers were not associated with the phenotype in F2. RNA-Seq analysis revealed 2,148 differentially expressed (P < 0.1) genes and 45,673 single nucleotide polymorphisms and >2,000 indels between BEH+/+ and BEL males. In conclusion, contrasting muscle traits and genomic and gene expression differences between BEH and BEL strains provide a promising model for the search for genes involved in muscle growth and musculoskeletal morphogenesis.

Analyses of muscle spindles in the soleus of six inbred mouse strains

Adult muscle size and fibre-type composition are heritable traits that vary substantially between individuals. We used inbred mouse strains in which soleus muscle mass varied by an order of magnitude to explore whether properties of muscle spindles can also be influenced by genetic factors. Skip-serial cross-sections of soleus muscles dissected from 15 male mice of BEH, BEL, C57BL/6J, DUH, LG/J and SM/J strains were analysed for number of muscle spindles and characteristics of intrafusal and extrafusal fibres following ATPase staining. The BEL and DUH strains determined the range of: soleus mean size, a 10-fold difference from 2.1 to 22.3 mg, respectively; the mean number of extrafusal fibres, a 2.5-fold difference from 497 to 1249; and mean fibre-cross-sectional area, three-fold difference, e.g. for type 1 fibres, from 678 to 1948 μm². The range of mean proportion of type 1 fibres was determined by C57BL/6J (31%) and DUH (64%) strains. The mean number of spindles per muscle ranged between nine (LG/J) and 13 (BEL) (strain effect P < 0.02). Genetic correlations between spindle count and muscle weight or properties of extrafusal fibres were weak and not statistically significant. However, there was a strong correlation between the proportion of spindles with more than one bag2 fibre and the proportion of extrafusal fibres that were of type 1, and strain-dependent variation in the numbers of such spindles was statistically significant. The numbers of intrafusal fibres per spindle ranged from 2 to 8, with the most common complement of four found in 75.6% of spindles. There were no significant differences between the strains in the mean numbers of intrafusal fibres; however, the variance of the number was significantly less for the C57BL/6J strain than for any of the others. We conclude that abundance of muscle spindles and their intrafusal-fibre composition are substantially determined by genetic factors, which are different from those affecting muscle size and properties of the extrafusal fibres.

Index selection in terminal sires improves lamb performance at finishing

Lamb meat is often perceived by consumers as fatty, and consumption has decreased in recent decades. A lean growth index was developed in the UK for terminal sire breeds to increase carcass lean content and constrain fat content at a constant age end point. The purposes of this study were 1) to evaluate the effects of index selection of terminal sires on their crossbred offspring at finishing and 2) to evaluate its effectiveness within terminal sire breeds. Approximately 70% of lambs marketed in the UK have been sired by rams of breeds typically thought of as specialized terminal sires. The most widely used are Charollais, Suffolk, and Texel. These breeds participated in sire referencing schemes from the early 1990s by sharing rams among flocks selected on the lean growth index. From 1999 to 2002 approximately 15 "high" and 15 "low" lean growth index score rams were selected from within their sire referencing schemes and mated to Welsh and Scottish Mule ewes. Their crossbred offspring were commercially reared on 3 farms in the UK. Lambs were finished to an estimated 11% subcutaneous fat by visual evaluation. At finishing, lambs were weighed, ultrasonically scanned, and assessed for condition score and conformation. Records were obtained for 6356 lambs on finishing BW (FWT), ultrasonic muscle depth (UMD), ultrasonic fat depth, overall condition score (OCS), and conformation of gigot, loin, and shoulder. Ultrasonic fat depth was log transformed (logUFD) to approach normality. High-index-sired lambs were heavier at finishing (1.2±0.2 kg) with thicker UMD (0.7±0.2 mm) and less logUFD (0.08±0.01 mm; P<0.05). There were no differences in OCS or conformation based on the sire index or breed (P>0.08). Suffolk-sired lambs were heavier than Charollais (1.0±0.3 kg), which were heavier than Texel (0.9±0.3 kg; P<0.001). Texel-sired lambs had thicker UMD than Charollais (0.7±0.2 mm; P<0.001) but were not different than Suffolk. Charollais-sired lambs had greater logUFD than both Texel (0.098±0.016 mm) and Suffolk (0.061±0.017 mm) sired lambs (P<0.001). Within a breed, high- and low-index-sired lambs differed in performance with the exceptions of FWT and UMD in Suffolks. Index selection produced heavier and leaner lambs at finishing. Producers have flexibility in choosing the terminal sire that best fits their production system.

Effects of selection on food intake in the adult mouse

SUMMARY

Replicated lines of mice were selected High and Low for adjusted food intake and contemporaneous control lines were maintained. The selection criterion was food intake between 8 and 10 weeks, adjusted by phenotypic regression on mean body weight at 8 and 10 weeks of age to reduce correlated changes in body weight. Responses are given for the first 23 generations of selection, after which adjusted food intake had diverged by a factor of 1.7-1.95. A small correlated response in body weight occurred and mice from the High line were slightly heavier: at 10 weeks of age body weight had diverged by a factor of 1.09-1.11. The realized within-family heritability varied between the replicates from 0.16-0.27 from which a mean estimated mass selection heritability (h(2) = 0.35±0.05) was derived. Mice from the Low line were fatter, however not significantly, because of a High between replicate variance (p > 0.05). Differences in growth over the selection period may account for around 5% of the divergence and increased maintenance costs associated with the larger lean mass of the high lines may explain a further 5%. Mice from the High lines spilled significantly (p < 0.05) more food which accounted for 23% of the divergence in apparent food intake. The heat increment of feeding, brown adipose tissue activity and locomotor activity all appear to be unchanged. ZUSAMMENFASSUNG: Auswirkungen der Selektion auf Futteraufnahme in der adulten Maus In einem Experiment mit Wiederholungen wurden Mäuselinien auf hohe und niedrige korrigierte Futteraufnahme selektiert und korrespondierende Konttrollen gehalten. Das Selektionskriterium war die Futteraufnahme im Alter von 8 bis 10 Wochen, die mittels phänotypischer Regression korrigiert wurde, um die Körpermasse möglichst konstant zu halten. Der direkte Selektionserfolg über die ersten 23 Generationen ist beschrieben. Die Linien divergierten zu diesem Zeitpunkt bezüglich des Selektionsmerkmals um 70 bis 95%. In der Körpermasse trat ein geringfügiger korrelierter Selektionserfolg auf. Die Tiere der 'high'-Linie waren im Alter von 8 bis Wochen ca. um 6 bis 11% schwerer. Die realisierte Intra-Familien-Heritabilität variierte zwischen den Wiederholungen zwischen 0.16 und 0.27, woraus sich eine mittlerer Heritabilitätskoeffizient von h(2) = 0.35±0.05 für die Massenselektion ergab. Mäuse der 'low'-Linie hatten mit 10 Wochen 2.4% (P > 0.05) und mit 17 Wochen ca. 7% (P < 0.05%) mehr Fett. Mit Unterschieden im Wachstum lassen sich weniger als 5% der Linienunterschiede in der Futteraufnahme erklären. Der höhere Erhaltungsbedarf, der aus einer höheren fett-freien Körpermasse in der 'high'-Linie resultiert, könnte weitere 5% erklären. Tiere der 'high'-Linie verstreuten deutlich (P < 0.05) mehr Futter, worauf sich 23% der Divergenz in der scheinbaren Futteraufnahme zurückführen ließen. Die Aktivät des braunen Fettgewebes, die lokomotorische Aktivität und die fütterungsbedingte Wàrmeproduktion sind scheinbar unverändert.

Mice with Low Metabolic Rates Are Not Susceptible to Weight Gain When Fed a High-Fat Diet

OBJECTIVE

Mice divergently selected for high or low food intake (FI) at constant body mass differ in their resting metabolic rates (RMRs). Low-intake individuals (ML) have significantly lower RMR (by 30%) compared with those from the high-intake line (MH). We hypothesized that MLs might, therefore, be more likely to increase their body and fat mass when exposed to a high-fat diet (HFD).

RESEARCH METHODS AND PROCEDURES

We exposed both lines to a diet with 44.9% calories from fat for 3 weeks while measuring FI, fecal production, and body mass and then returned the mice to standard chow.

RESULTS

When exposed to the HFD, both lines significantly decreased their FI (MH, 40% to 45%; ML, 31% to 35%). This decrease occurred simultaneously with a significant increase in apparent energy absorption efficiency (AEAE). When returned to chow, FI and AEAE returned to the levels observed prior to HFD exposure. Because of the adjustments in FI, the absorbed energy was maintained in the MLs and, thus, body mass remained constant. The MH individuals overcompensated for the elevated energy content and AEAE on the HFD and, therefore, absorbed lower energy than when feeding on chow. These mice also did not significantly change their body mass when on the HFD and must have made adjustments in their energy expenditures. Both lines and both sexes increased in fat content on the HFD, but these effects were not different between lines or sexes.

DISCUSSION

We found no support for the hypothesis that mice with low RMRs were more susceptible to weight gain when fed the HFD.

Bayesian meta-analysis of the effect of fasting, transport and lairage times on four attributes of pork meat quality

Technological meat quality is a significant economic factor in pork production, and numerous publications have shown that it is strongly influenced both by genetic status and by rearing and slaughter conditions. The quality of meat is often described by meat pH at different times postmortem, as well as by color and drip loss. A meta-analysis based on a database built from 27 studies corresponding to a total of 6526 animals classified was carried out. The purpose of this meta-analysis was to study the effect of fasting, lairage and transport durations on four main attributes of the technological pork meat quality. A Bayesian hierarchical meta-regression approach was adopted. The results of our meta-analysis showed that fasting time had a significant effect on pH measured 24h post-mortem (pHu) and drip loss (DL) measured in longissimus muscle. While, lairage affected only the pHu in semimembranosus muscle. Interestingly, we found that DL was the lone attribute that was affected by transport time and its interaction with fasting time.

Factors affecting dystocia and offspring vigour in different sheep genotypes

Birth difficulty and poor lamb vigour are significant causes of perinatal lamb mortality. In this study we investigated whether sheep breeds differing in appearance, muscularity and selection history also had differences in dystocia and lamb vigour, and considered some of the factors that may contribute to the variation in these traits. Data were collected at birth from a total of 3252 lambs of two terminal sire breeds selected for lean growth (Suffolk [S], n=500 and Texel [T], n=1207), from a Hill breed (Scottish Blackface [B], n=610), which has been mainly selected for hardiness, and a crossbred (Mule×T [M], n=935) representing a maternal line. For each lamb the degree of assistance at delivery, lamb presentation, amount of assistance to achieve successful sucking, sex, litter size and birth weight were recorded. T lambs required the most, and B and M lambs the least assistance at birth, S lambs were intermediate (% lambs assisted: T=55.7, S=30.7, B=22.7, M=24.9, P<0.001). T and S lambs were equally likely to be malpresented at birth (29% of births) and more likely to be malpresented than B or M lambs (20%; P<0.001). In T and S breeds lambs requiring veterinary assistance at delivery were mainly heavy and singleton lambs, whereas in B and M breeds these were exclusively low birth weight lambs in multiple litters. Although heavier lambs needed greater birth assistance, T lambs were lighter than S and M lambs, but heavier than B lambs (birth weight (kg): S=4.66, M=4.56, T=4.32, B=3.67, P<0.001). S lambs were more likely to require assistance with sucking than other breeds, and T lambs also required more assistance than B or M lambs (% lambs assisted to suck: S=56.0, T=31.6, M=19.8, B=18.4, P<0.001). Heavier lambs were more likely to suck unaided than lighter lambs (P<0.001). The data suggest that the two terminal sire breeds, selected narrowly for greater productivity (muscle growth and conformation), are more likely to experience birth difficulty and poorer lamb vigour than the breed selected for hardiness, or the cross breed. Whether these effects arise as a consequence of genetic selection (e.g. for specific lamb conformation), or as a result of management practices to achieve selection goals (e.g. increased intervention at lambing) is unknown. Specific actions to improve birth difficulty and lamb vigour, such as including these traits in the selection index, would be beneficial in improving the welfare of ewes and lambs of the terminal sire breeds.

Comparison of repeatability and multiple trait threshold models for litter size in sheep using observed and simulated data in Bayesian analyses

Bayesian analyses were used to estimate genetic parameters on 5580 records of litter size in the first four parities from 1758 Mule ewes. To examine the appropriateness of fitting repeatability (RM) or multiple trait threshold models (MTM) to litter size of different parities, both models were used to estimate genetic parameters on the observed data and were thereafter compared in a simulation study. Posterior means of the heritabilities of litter size in different parities using a MTM ranged from 0.12 to 0.18 and were higher than the heritability based on the RM (0.08). Posterior means of the genetic correlations between litter sizes of different parities were positive and ranged from 0.24 to 0.71. Data sets were simulated based on the same pedigree structure and genetic parameters of the Mule ewe population obtained from both models. The simulation showed that the relative loss in accuracy and increase in mean squared error (MSE) was substantially higher when using the RM, given that the parameters estimated from the observed data using the opposite model are the true parameters. In contrast, Bayesian information criterion (BIC) selected the RM as most appropriate model given the data because of substantial penalty for the higher number of parameters to be estimated in the MTM model. In conclusion, when the relative change in accuracy and MSE is of main interest for estimation of breeding values of litter size of different parities, the MTM is recommended for the given population. When reduction in risk of using the wrong model is the main aim, the BIC suggest that the RM is the most appropriate model.

Meta-analysis of the effects of dietary vitamin E supplementation on α-tocopherol concentration and lipid oxidation in pork

Meta-analyses have been carried out to quantify the effect of dietary vitamin E on α-tocopherol accumulation and on lipid oxidation in porcine M. longissimus. Published results of 13 (vitamin E accumulation) and 10 (lipid oxidation) experiments respectively were used for the analyses. After a number of standardization procedures, a nonlinear relationship was found between the supplementary vitamin E and the accumulation of α-tocopherol in pork which approached a maximum value of 6.4 μg/g tissue. Pork lipid oxidation levels were described in terms of Thiobarbituric Acid Reacting Substances (TBARS) values. The statistical analysis revealed significant effect of vitamin E dose, muscle α-tocopherol concentration and supplementation time on TBARS, resulting in two prediction models for lipid oxidation. Meta-analysis has proven to be a valuable tool for combining results from previous studies to quantify the effects of dietary vitamin E. Further studies, carried out with standardized experimental protocols would be beneficial for model validation and to increase the predictive power of the derived models.

Meta-analysis of effects of dietary vitamin E and post slaughter storage conditions on changes of redness (a*) of pork

Abstract. A meta-analysis was carried out to quantify the effects of dietary vitamin E and storage conditions on colour changes of pork from M. longissimus dorsi. After standardisation procedures, redness of pork (CIE colour specification a*), one of the most important objective colour attributes, was used as an indicator for colour changes in this analysis. The analysis was based on results from five experiments, which met selection criteria. Analysis of changes of other objective colour attributes, lightness (L*) and yellowness (b*) was not possible due to lack of published data. The statistical analysis (using mixed models) found significant effects of tissue α-tocopherol concentration in M. longissimus dorsi, simplified supplemented vitamin E levels as well as storage time and storage light on redness of pork and its changes over time. The relationship between redness and α-tocopherol concentration was found to be linear, and between redness and storage time was non-linear (third degree polynomial) in one model. This model suggested that an increase of 1 μg of α-tocopherol in the muscle led to an expected increase a* value of 0.11. Another model identified significant interactions about 0.28 between α-tocopherol concentration and storage time in late storage periods. A third model found a significant difference of −0.48 between predicted a* values at lower (≤50 IU/kg feed) and higher supplemented vitamin E levels (≥100 IU/kg feed). The models predicted an initial increase for 3 days, a stable period for 5 days and then a decrease for a* values over storage time. The a* values were significantly lower by about 1.4 when samples were exposed to light in the models, the effect of light found to be constant over time. Further studies, carried out with standardized methods, are needed to increase the predictive power of the derived models and to validate the models for other muscles.

Genetic relationship between longevity and objectively or subjectively assessed performance traits in sheep using linear censored models

Genetic parameters of longevity in crossbred Mule ewes, and genetic relationships among longevity, growth, body composition, and subjectively assessed traits on Mule lambs and ewes have been estimated using Bayesian linear censored models. Additionally, the genetic associations between longevity and culling reasons were examined. Data comprised 1,797 observations of Mule ewes for longevity, culling reasons, growth, body composition, mouth scores, and type traits. Longevity was defined as the time (in years) from 2 yr of age (the age at first lambing of most ewes) to culling or death. Censored data (i.e., observations for which only the lower bound of the true longevity is known, such as when the animals are still alive) comprised 24% of all observations for longevity. Bivariate analyses were used to analyze the longevity of the ewe with each performance trait by fitting linear Bayesian models considering censored observations. Longevity was split into 3 different sub-traits: age at culling due to teeth/mouth conditions, age at culling due to udder conditions, and age at culling due to other culling reasons. These sub-traits and their aggregation into the overall trait of longevity were analyzed in a multiple-trait model. The heritability of longevity was moderate at 0.27, whereas heritabilities of the growth and body composition traits ranged from 0.11 for average of shoulder, loin, and gigot conformation to 0.36 for ewe BW at first premating. Mouth scores and type traits had heritabilities ranging from 0.13 for jaw position to 0.39 for fleece quality. All analyzed traits showed low genetic correlations with longevity, ranging from -0.20 for average conformation scores in live animals to 0.18 for tooth angle. Teeth/mouth conditions resulted in the greatest heritability (0.15) among the sub-traits based on the separate culling reasons. Genetic correlations between separate culling reasons were low to high (0.12 to 0.63 for teeth/mouth conditions with udder conditions and other culling reasons, respectively). Longevity may be preferred as a selection criterion because of (i) its moderate heritability compared with its component sub-traits based on specific culling reasons, and (ii) its moderate to high genetic correlation with these component sub-traits. The moderate heritability for longevity reflects the potential of this trait for genetic improvement, especially when longevity is based on clearly defined culling reasons.

Genetic parameters for carcass composition and performance data in crossbred lambs measured by Video Image Analysis

A total of 7074 crossbred lambs, produced by mating crossbred Mule ewes with terminal sire rams were used in this study. Of these, 630 were scanned using a Video Image Analysis (VIA) to estimate carcass quality traits. Genetic parameters for average daily gain (ADG), scanning live weight (SW), ultrasonic measures of muscle (UMD) and fat (UFD) depths, cold carcass weight (CCW) and VIA measurements of primal carcass joint weights (LEG, CHUMP, LOIN, BREAST and SHOULDER) were estimated using multivariate animal models. Additionally, VIA traits were evaluated under a repeatability model, considering the primal joints as repeated measures of the same trait. Direct heritability estimates were low to moderate (0.08-0.26) for VIA measurements of primal joints. Repeatability estimates for VIA traits were high (>0.90). Moderate to high heritability estimates (0.25-0.55) were found for performance traits (ADG, SW, UMD and UFD) and CCW. Genetic correlations between VIA traits and ADG were strong (0.75-0.93). Most of the VIA traits were highly correlated to SW (0.60-0.97). UFD was significantly negatively correlated with UMD (-0.22), ADG (-0.18) and CCW (-0.18). The results of this study suggest that selection on performance and carcass traits, measured by VIA, could possibly improve primal meat yield of carcass cuts without increasing the overall carcass fatness. High repeatability estimates of VIA traits and moderate heritabilities of the most valuable carcass joints suggests that including VIA information in breeding programs would be useful in order to improve carcass quality.

Breeding for resistance to mastitis in United Kingdom sheep, a review and economic appraisal

Mastitis is a problem in the sheep industry, and its incidence varies widely with how it is recorded, the breed of sheep and the farm. Virtually all the published information about the genetics of mastitis refers to dairy breeds of cattle and sheep, and there is little information for meat sheep breeds. Many dairy breeding programmes worldwide use the somatic cell count (scc) in milk as an indicator of resistance to clinical and subclinical mastitis, but it is difficult to measure in meat sheep breeds. Molecular genetic technologies may therefore be a more practical way to assess susceptibility to mastitis. This paper reviews the genetics of mastitis and considers the opportunities for breeding for resistance to mastitis, with particular reference to sheep. In addition, to investigate the potential economic effects of mastitis in a purebred sheep population, a computer model of flock dynamics was developed. By making a modest set of assumptions about the key farm parameters that influence lowland sheep production, the model showed that breeding for resistance (or other control methods), if it could reduce the risk of contracting mastitis by 10 per cent, would be worth pounds 8.40 per ewe, equivalent annually to pounds 2.7 million for the purebred sector of the Texel breed alone.

Breeding for resistance to footrot--the use of hoof lesion scoring to quantify footrot in sheep

So that genetic studies can be undertaken on footrot in sheep, it is necessary that a reliable and repeatable method to categorise the phenotype is available. This paper summarises the methods used and results obtained from 1600 hoof lesion scores of 100 mixed-age ewes independently scored twice by two trained operators. Using a 5-pont scale describing the severity of foot lesions, residual correlations were used to assess agreement between scorers and scoring occasions. Data were analysed using both zero-1 and continuous data methods. The average prevalence of any score >0 was 15%, and of scores >1 was 12%. The residual correlation between scorers for SUM_FR was 0.87 and between scoring occasions it was also 0.87, indicating high repeatability or agreement both within and between scorers. No significant differences were detected between scorers or between scoring occasions for any of the traits analysed, or different analytical methods used.

Divergent physical activity and novel alternative responses to high fat feeding in polygenic fat and lean mice

We determined whether altered physical activity levels might underlie the contrasting adiposity of a divergently selected polygenic murine model of metabolic syndrome (Fat; F) and leanness (Lean; L) mice. We measured physical activity with a long term running wheel experiment and performed an additional high fat diet intervention. Further, we measured posture allocation by visual monitoring within the home cage as a non-exercise correlate of 'normal' physical activity. Whilst initially similar, running wheel activity of the F line declined with age, while the activity of the L line increased. Food intake was higher in the L line and increased with wheel exposure. Vertical rearing measured by video quantification in the home cage, without the stimulus of a running wheel was also significantly higher in the L line. The two lines developed novel alternate strategies to defend their body weight when exposed to high fat diets with a running wheel. F mice increased their running wheel activity, and despite unaltered food intake, still gained weight. L mice reduced their food intake and maintained activity levels without a significant change in body weight. Phenotypic selection for divergence in body fat content has co-segregated with a genetic predisposition for divergent physical activity levels and different strategies for coping with exposure to high fat diets that will facilitate the discovery of the genes underlying these important obesity related traits.

Fine mapping of mouse QTLs for fatness using SNP data

Quantitative trait loci (QTLs), as determined in crossbred studies, are a valuable resource to identify genes responsible for the corresponding phenotypic variances. Due to their broad chromosomal extension of some dozens of megabases, further steps are necessary to bring the number of candidate genes that underlie the detected effects to a reasonable order of magnitude. We use a set of 13,370 SNPs to identify informative haplotype blocks in 22 mouse QTLs for fatness. About half of the genes in a typical QTL overlap with haplotype blocks, which are different for the two base mouse lines, and which, thus, qualify for further analysis. For these genes we collect four more pieces of evidence for association with fat accumulation, namely (1) homology to genes identified in a Caenorhabditis elegans knock-out experiment as fat decreasing or fat increasing, (2) the overexpression of the genes in mouse fat, liver, muscle, or hypothalamus tissues, (3) the occurrence of a gene in several independently found QTLs, and (4) the information provided by gene ontology, to achieve a ranked list of 131 candidate genes. Ten genes fulfill three or four of the above sketched criteria and are discussed briefly, 121 further genes fulfilling two criteria are provided as on-line material. Viewing the genomic region of fatness-related QTLs under several different aspects is appropriate to assess the many thousands of genes that reside in such QTLs and to produce lists of more robust candidate genes.

Quantitative trait Loci for regional adiposity in mouse lines divergently selected for food intake

OBJECTIVE

Obesity is thought to result from an interaction between genotype and environment. Excessive adiposity is associated with a number of important comorbidities; however, the risk of obesity-related disease varies with the distribution of fat throughout the body. The aim of this study was to map quantitative trait loci (QTLs) associated with regional fat depots in mouse lines divergently selected for food intake corrected for body mass.

RESEARCH METHODS AND PROCEDURES

Using an F2 intercross design (n = 457), the dry mass of regional white (subcutaneous, gonadal, retroperitoneal, and mesenteric) adipose tissue (WAT) and brown adipose tissue (BAT) depots were analyzed to map QTLs.

RESULTS

The total variance explained by the mapped QTL varied between 12% and 39% for BAT and gonadal fat depots, respectively. Using the genome-wide significance threshold, nine QTLs were associated with multiple fat depots. Chromosomes 4 and 19 were associated with WAT and BAT and chromosome 9 with WAT depots. Significant sex x QTL interactions were identified for gonadal fat on chromosomes 9, 16, and 19. The pattern of QTLs identified for the regional deposits showed the most similarity between retroperitoneal and gonadal fat, whereas BAT showed the least similarity to the WAT depots. Analysis of total fat mass explained in excess of 40% of total variance.

DISCUSSION

There was limited concordance between the QTLs mapped in our study and those reported previously. This is likely to reflect the unique nature of the mouse lines used. Results provide an insight into the genetic basis of regional fat distribution.

Testing selection indices for sustainable hill sheep production – lamb growth and carcass traits

Two selection indexes, one intended for lamb producers and finishers and one for store lamb producers, were derived using genetic parameters for carcass and maternal characteristics from Conington et al. (2001) and economic values from Conington et al. (2004). This paper summarizes responses to selection for lamb traits only, after 5 years of selection (1998 to 2003) on two farms using these selection indexes. The index for lamb producers and finishers, evaluated on farm 1, with a flock size of 680 ewes, includes economic weightings for maternal traits as well as carcass weight, fat and conformation grades, whereas the index for store lamb producers, evaluated on farm 2, with a flock size of 580 ewes, only includes economic values for maternal traits and lamb growth to weaning. Three selection lines of Scottish Blackface sheep per farm were created with the first lambs born to each line in 1999. These lines were selection (S), control (C) and industry (I); they were of equal size on each farm. Five top- and five average-performing ram lambs were selected each year for the S and C lines respectively using a multi-trait best linear unbiased prediction (BLUP) implementation of the indexes. The I-line used four mature rams bought from industry, selected on appearance only, i.e. adherence to breed ‘type’. Results showed that 5 years after the implementation of the index, the S line had significantly higher index scores than the C or I lines on both farms. The means (s.d.) for the average index scores in 2003 are 114 (328), 119 (371) and 451 (328) (farm 1), and −8 (146), −11 (130), and 250 (129) (farm 2) for the C, I and S lines, respectively, giving predicted net differences (S-C) of £3·38 (farm 1) and £2·58 (farm 2) per ewe. Phenotypic responses showed significant S v. C differences in weaning weight on both farms. As predicted from previous analyses, no changes in carcass quality traits were seen at farm 1 although S-line carcass weights tended to be heavier than those from the C or I lines. The results show that genetic improvement using multi-trait selection indices has been successful and it is a viable, long-term strategy to improve levels of production for hill sheep in extensive environments.

In vivo measurements of muscle volume by automatic image analysis of spiral computed tomography scans

This study investigates the accuracy of an automatic image analysis method that was developed for spiral computed tomography scans (SCTS), with the objective of calculating the volume of muscle in the hind leg (HLMVCT) and lumbar region (LRMVCT) in lambs. The first step in the image analysis method was the isolation (segmentation) of the muscle regions in each image of the SCTS, using a new program that was implemented in the Sheep Tomogram Analysis Routines software (STAR). Due to the differences of muscle shape in the regions investigated, the new segmentation program applies different segmentation paths in specific subregions. These were automatically identified by the program based on skeletal landmarks. After the segmentation was completed, the muscles areas were automatically measured by counting the pixels representing muscle in each image; the volumes were calculated by adding the muscle areas of each image multiplied by the depth of the image (inter-slice distance). The accuracy of these measures of muscle volume was evaluated, using regression analysis, by comparing HLMVCT and LRMVCT to the hind leg and lumbar region muscle weights measured after dissection (HLMWD, no. =240, and LRMWD, no. =50, respectively) of Texel (TEX) and Scottish Blackface (SBF) female and male lambs slaughtered in 2003-04. The effects of breed, sex and year on the association (SCTS v. dissection) were evaluated. There was a strong association between HLMVCT and HLMWD ( R2=97·4%), which only increased slightly ( R2=97·7%) when breed was included in the model. This indicates that HLMWD can be estimated directly from HLMVCT with a high degree of accuracy. For the lumbar region, the association was high ( R2=83·0% to 88·8% depending on the model) but lower than in the hind leg, probably because the automatic segmentation isolates only the areas of the longissimus lumborum and multifidi muscles. Breed had a significant effect on the prediction of LRMWD from LRMVCT, as well as sex in the case of the TEX lambs. The results indicated that the predictions of LRMWD from LRMVCT require different equations for very divergent breeds such as TEX and SBF.

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.

Accuracy of in vivo muscularity indices measured by computed tomography and their association with carcass quality in lambs

Assessments of muscle mass and skeletal dimensions by Computed Tomography (CT) enable the development of new muscularity indices for the hind leg (HL) and lumbar region (LR) in lambs. Compared to previous CT muscularity indices, the accuracy was much higher with the new index in the HL (correlations between CT and dissection indices of 0.89 vs 0.51). The accurate measurement of femur length by CT used in the calculation of the new HL index made an important contribution to the higher accuracy of the index. The improvement in accuracy was smaller for the LR (0.55 vs 0.44). The association of CT muscularity indices and carcass quality in Texel and Scottish Blackface lambs showed that improved muscularity is not phenotypically correlated with detrimental effects on carcass composition. CT muscularity indices provide an alternative method to improve carcass conformation and leanness, using measurements that at a constant weight are independent of fatness.

Associations of polymorphisms of the ovine prion protein gene with growth, carcass, and computerized tomography traits in Scottish Blackface lambs

The objective of this study was to investigate and estimate the associations of the ovine prion protein (PrP) genotypes with a wide range of performance traits in Scottish Blackface lambs. Performance records of up to 7,138 sheep of known PrP genotypes born from 1999 to 2004 in 2 experimental farms were utilized. Performance traits studied were BW at birth, marking (when the sheep were identified with permanent ear tags at an average age of 52 d), and weaning (average age of 107 d); slaughter traits (BW at slaughter, slaughter age, carcass weight, and carcass conformation); ultrasonic muscle and fat depths; and computerized tomography-predicted carcass composition and carcass yield at weaning. Different linear mixed models, including random, direct animal effect, and up to 3 maternal effects (genetic, permanent, and temporary environmental) were used for the different traits. The PrP genotype was included in the model as a fixed effect, along with other fixed factors with significant effects (P < 0.05). Five separate analyses were carried out for each trait, differing in the method of PrP genotypic classification. The first analysis was based on classifying the sheep into categories according to all 9 available PrP genotypes. In the other 4 analyses, sheep were categorized according to the number of each PrP allele carried. Results showed that there were no significant differences between PrP genotypes for any of the performance traits studied when all 9 genotypes were compared (first analysis). Similarly, performance of the lambs did not significantly differ between genotypes with different numbers of ARR copies. However, there were significant variations in a few traits with respect to the number of ARQ, AHQ, and VRQ alleles carried. Heterozygous lambs for the AHQ or the ARQ allele were significantly heavier at some ages than lambs of the other genotypes. Lambs carrying the VRQ allele required approximately 10 d longer finishing time (P = 0.01) and yielded carcasses approximately 0.5 kg heavier (P = 0.03) compared with noncarriers. The few significant associations found do not have a negative influence on performance when selecting against the most susceptible PrP allele (VRQ) or in favor of the most resistant one (ARR). Overall, there were no major associations of PrP genotypes with most lamb performance traits in Scottish Blackface sheep.

A genetic investigation of various growth models to describe growth of lambs of two contrasting breeds1

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 Akaike's 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.

In vivo prediction of internal fat weight in Scottish Blackface lambs, using computer tomography

From a calibration trial involving computer tomography (CT) scanning and dissection of 45 lambs, a prediction equation was derived to estimate total internal fat weight in Scottish Blackface lambs from measurements taken on cross-sectional CT images. Using data from two cross-sectional images (at the hip and loin) internal fat can be predicted with relatively high accuracy (adjusted R(2) = 62.2%, r = 0.79). The derived equation was then used to predict internal fat weights in a further 427 Scottish Blackface lambs from a separate trial. Phenotypic correlations were calculated between predicted internal fat weight and weights of total carcass fat, muscle and bone, predicted using previously derived equations. When considering absolute tissue weights, adjusted for fixed effects, internal fat showed the strongest positive correlation with carcass fat (0.58), followed by muscle (0.36), and then by bone (0.32). When tissue weights were adjusted for fixed effects and total carcass weight (so considering tissue weights relative to size), internal fat showed a lower correlation with carcass fat weight (0.36) and negative correlations with muscle (-0.35) and bone (-0.19). These results provide the basis for more complex studies of relationships (phenotypic and genetic) between internal fat in hill lambs and economically important traits, such as carcass composition and survival of lambs, and tissue levels in different depots in hill ewes.

A polygenic model of the metabolic syndrome with reduced circulating and intra-adipose glucocorticoid action

Despite major advances in understanding monogenic causes of morbid obesity, the complex genetic and environmental etiology of idiopathic metabolic syndrome remains poorly understood. One hypothesis suggests that similarities between the metabolic disease of plasma glucocorticoid excess (Cushing's syndrome) and idiopathic metabolic syndrome results from increased glucocorticoid reamplification within adipose tissue by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD-1). Indeed, 11beta-HSD-1 is now a major therapeutic target. Because much supporting evidence for a role of adipose 11beta-HSD-1 comes from transgenic or obese rodents with single-gene mutations, we investigated whether the predicted traits of metabolic syndrome and glucocorticoid metabolism were coassociated in a unique polygenic model of obesity developed by long-term selection for divergent fat mass (Fat and Lean mice with 23 vs. 4% fat as body weight, respectively). Fat mice exhibited an insulin-resistant metabolic syndrome including fatty liver and hypertension. Unexpectedly, Fat mice had a marked intra-adipose (11beta-HSD-1) and plasma glucocorticoid deficiency but higher liver glucocorticoid action. Furthermore, metabolic disease was exacerbated only in Fat mice when challenged with exogenous glucocorticoids or a high-fat diet. Our data suggest that idiopathic metabolic syndrome might associate with such a novel pattern of glucocorticoid action and sensitivity in humans, with implications for tissue-specific therapeutic targeting of 11beta-HSD-1.