Relationships between lamb carcass quality traits measured by X-ray computed tomography and current UK hill sheep breeding goals

Genetic parameters were estimated between current UK hill sheep breeding goals and lamb carcass composition and muscularity traits derived using X-ray computed tomography (CT). To produce these estimates, a total of 648 lambs from two hill farms were CT scanned at weaning (ca 120 days of age), over 3 years, and total weights of carcass muscle (MUSC), fat (CFAT) and bone (BONE) and internal fat (IFAT) were predicted. Previously derived muscularity indices were also calculated for the hind leg (HLMI) and lumbar (LRMI) regions, to assess muscle shape. Data for current breeding goals (lamb performance and maternal traits) were also included from a total of 10 297 lamb records and 12 704 ewe records. Heritabilities were estimated for each trait and genetic and phenotypic correlations were calculated between each CT trait and other lamb or ewe traits. Moderate to high positive genetic correlations were found between CT-predicted tissue weights and breeding goals, which were also weights (lamb weaning weight, carcass weight, mature ewe weight, average weight of lambs reared by the ewe). CFAT was positively genetically correlated with ultrasound backfat depth at weaning (UFD) and subjective fatness grade at slaughter (MLCF), suggesting that carcass fat could be decreased using selection on any of these predictors. Ultrasound muscle depth at weaning (UMD) and subjective conformation score at slaughter (MLCC) had high genetic correlations with the muscularity indices (HLMI and LRMI), but correlations with MUSC were not significantly different from zero. This implies that selection to improve MLCC is likely to be increasing the 'roundness' of muscle shape in the high-priced carcass region, but having little impact on total lean meat yield. Correlations of CT traits with the other ewe traits (number of lambs weaned, number of lambs lost, longevity, fleece weight) were generally small or not significantly different from zero. The genetic parameters generated in this study can now be used in selection index calculations to assess the benefits of including lamb CT traits in future selection programmes for hill sheep.     

The effects of selection indices for sustainable hill sheep production on carcass composition and muscularity of lambs, measured using X-ray computed tomography

A multi-trait selection index designed to improve the overall economic performance of hill sheep, including both maternal and lamb traits, has been developed and tested in a selection experiment over 7 years. Two versions of the index were tested, with different economic weights applied to the traits, on two different hill farms: one version including maternal and growth traits; the other version with additional breeding goals of carcass weight, fatness and conformation scores. Responses to selection, using both versions of the index, suggest that improvements are being made in overall index score and lamb growth. This study investigated the indirect effects of these selection indices on lamb carcass composition and muscularity traits, as measured using X-ray computed tomography (CT) scanning. A total of 499 lambs from the two hill farms were CT scanned at weaning (approximately 120 days of age). Approximately half of the lambs from each farm were from the selection line (S, animals with highest index scores selected for breeding), while the other half were from a control line (C, animals with average index scores selected). Composition and muscularity traits were estimated on each lamb from CT data and differences between genetic lines investigated, within farm, using restricted maximum likelihood analyses, adjusting for either live weight or age. Results showed that the selection index without carcass traits produced lambs with carcass composition that was not significantly different to control lambs at a given live weight or age. Including carcass traits in the index resulted in lambs with no compositional differences (except for a slight increase in bone) at a set age compared with controls. At a given live weight however, selection lambs had less fat and lower carcass weights and killing-out percentage. Muscularity (3-D muscle shape) and muscle area shape (2-D) were not improved as a result of selection on either version of the index (including carcass weight and grades in the breeding goals or not) and, at a fixed live weight, muscularity in hind leg and lumbar regions tended to be higher in the C line. To accelerate changes in carcass composition and muscularity within the context of a multi-trait selection index for hill sheep, consideration should therefore be given to including objective CT-derived carcass traits in the index in addition to the Meat and Livestock Commission (MLC) carcass grades or ultrasound measurements.     

Effects of a quantitative trait locus for increased muscularity on carcass traits measured by subjective conformation and fat class scores and video image analysis in crossbred lambs

A quantitative trait locus (QTL) for increased loin muscularity (TM-QTL) has previously been identified in purebred Texel sheep. Crossbred lambs born out of Mule ewes mated to heterozygous Texel sires for the TM-QTL were evaluated for a range of carcass traits. Lambs were genotyped and classified as carriers (n = 62) of a single copy of the TM-QTL and non-carriers (n = 49). In this study, the effects of the TM-QTL on carcass attributes were investigated using subjective classification scores for conformation and fatness, and measurements from a video image analysis (VIA) system. In addition, refined prediction equations to estimate weights of primal joints (leg, chump, loin, breast and shoulder) were obtained by calibrating the VIA system against computer tomography (CT) measurements in the loin region. The new refined prediction models increased the accuracy of prediction of all primal cuts on an average of 16% compared to previously derived standard VIA prediction equations. The coefficient of determination (R2) of the VIA system to predict in vivo CT measurements ranged from 0.39 to 0.72 for measurements of Musculus longissimus lumborum (MLL) area, width and depth, lumbar spine length, loin muscle volume and loin muscularity index. Using VIA estimates of CT-measured loin muscle traits, a significant increase in depth (+2.7%) of the MLL was found to be associated with the TM-QTL. Conformation and fatness scores and the shape of the carcass measured as individual lengths, widths and areas by VIA were not significantly influenced by the TM-QTL. Primal meat yields estimated using both standard and refined VIA prediction equations were not significantly affected by the TM-QTL. However, carcass 'compactness' was found to have significantly increased in carrier lambs. The weight of the dissected MLL estimated using VIA information was greater (+2.6%) for carriers compared to non-carriers. To conclude, neither the current industry carcass evaluation system for conformation and fatness nor the standard VIA system is able to identify the effect of the TM-QTL in the loin region in the moment. However, the calibration of the VIA system against CT measurements resulted in improved VIA prediction equations for primal meat yields and also showed moderate potential to estimate loin muscle traits measured by CT and to detect, partially, the effect of the TM-QTL on these traits.     

Live animal measurements, carcass composition and plasma hormone and metabolite concentrations in male progeny of sires differing in genetic merit for beef production

In genetic improvement programmes for beef cattle, the effect of selecting for a given trait or index on other economically important traits, or their predictors, must be quantified to ensure no deleterious consequential effects go unnoticed. The objective was to compare live animal measurements, carcass composition and plasma hormone and metabolite concentrations of male progeny of sires selected on an economic index in Ireland. This beef carcass index (BCI) is expressed in euros and based on weaning weight, feed intake, carcass weight and carcass conformation and fat scores. The index is used to aid in the genetic comparison of animals for the expected profitability of their progeny at slaughter. A total of 107 progeny from beef sires of high (n = 11) or low (n = 11) genetic merit for the BCI were compared in either a bull (slaughtered at 16 months of age) or steer (slaughtered at 24 months of age) production system, following purchase after weaning (8 months of age) from commercial beef herds. Data were analysed as a 2 × 2 factorial design (two levels of genetic merit by two production systems). Progeny of high BCI sires had heavier carcasses, greater (P < 0.01) muscularity scores after weaning, greater (P < 0.05) skeletal scores and scanned muscle depth pre-slaughter, higher (P < 0.05) plasma insulin concentrations and greater (P < 0.01) animal value (obtained by multiplying carcass weight by carcass value, which was based on the weight of meat in each cut by its commercial value) than progeny of low BCI sires. Regression of progeny performance on sire genetic merit was also undertaken across the entire data set. In steers, the effect of BCI on carcass meat proportion, calculated carcass value (c/kg) and animal value was positive (P < 0.01), while a negative association was observed for scanned fat depth pre-slaughter and carcass fat proportion (P < 0.01), but there was no effect in bulls. The effect of sire expected progeny difference (EPD) for carcass weight followed the same trends as BCI. Muscularity scores, carcass meat proportion and calculated carcass value increased, whereas scanned fat depth, carcass fat and bone proportions decreased with increasing sire EPD for conformation score. The opposite association was observed for sire EPD for fat score. Results from this study show that selection using the BCI had positive effects on live animal muscularity, carcass meat proportion, proportions of high-value cuts and carcass value in steer progeny, which are desirable traits in beef production.     

A comparative analysis of carcass and meat traits,and rumen bacteria between Chinese Mongolian sheep and Dorper × Chinese Mongolian crossbred sheep

Mutton is one of the most widely consumed meats globally. The Chinese Mongolian sheep (MS) breed is an indigenous breed of sheep characterised by high-quality meat and strong adaptability. Dorper × Chinese Mongolian crossbred sheep (DS) is an improved breed with a rapid growth rate and high mutton yield found in parts of China. The rumen microbiota is known to play a key role in shaping host nutrition and health. However, the carcass traits and meat nutritional qualities of DS and MS remain poorly defined, as does how rumen microbes affect these characteristics. The objective of this study was to compare carcass profiles, rumen bacterial communities, and meat nutritional qualities between MS and DS and clarify the associations between rumen microbiota and meat nutritional composition. We found that DS had a faster growth rate and better carcass traits than MS, including BW, carcass weight, meat weight, and loin-eye area. We further found that metabolite and rumen bacterial community composition differed between the two sheep breeds. First, compared with MS, DS had lower contents of some sweet amino acids, monounsaturated fatty acids, n-3 polyunsaturated fatty acids, and beneficial metabolites. Secondly, MS and DS had distinct rumen bacterial compositions, and these differential bacteria were related to carcass traits as well as to contents of meat amino acids, free fatty acids, and other metabolites. Taken together, our data showed that DS had better carcass characteristics but lower meat nutritional quality, parameters that were associated with differences in rumen bacterial community composition. These findings may benefit future breeding strategies aimed at improving sheep carcass performance and meat quality worldwide.     

Formulation of a decision support tool incorporating both genetic and non-genetic effects to rank young growing cattle on expected market value

While breeding indexes exist globally to identify candidate parents of the next generation, fewer tools exist that provide guidance on the expected monetary value of young animals. The objective of the present study was therefore to develop the framework for a cattle decision-support tool which incorporates both the genetic and non-genetic information of an animal and, in doing so, better predict the potential market value of an animal, whatever the age. Two novel monetary indexes were constructed and their predictive ability of carcass value was compared to that of the Irish national Terminal breeding index, typical of other terminal indexes used globally. A constructed Harvest index was composed of three carcass-related traits [i.e., 1) carcass weight, 2) carcass conformation and 3) carcass fat, each weighted by their respective economic value] and aimed at purchasers of animals close to harvest; the second index, termed the Calf index, also included docility and feed intake (weighted by their respective economic value), thus targeting purchasers of younger calves for growing (and eventually harvesting). Genetic and non-genetic fixed and random effect model solutions from the Irish national genetic evaluations underpinned all indexes. The two novel indexes were formulated using three alternative estimates of an animal's total merit for comparative purposes: 1) an index based solely on the animal's breed solutions, 2) an index which also included within-breed animal differences, and 3) an index which, as well as considering additive and non-additive genetic effects, also included non-genetic effects (referred to as production values [PVs]). As more information (i.e., within breed effects and subsequently non-genetic effects) was included in the total merit estimate, the correlations strengthened between the two proposed indexes and the animal's calculated carcass market value; the correlation coefficients almost doubled in strength when total merit was based on PV-based estimates as compared to the breed solutions alone. Including phenotypic live-weight data, collected during the animal's life, strengthened the predictive ability of the indexes further. Based on the results presented, the proposed indexes may fill the void in decision support when purchasing or selling cattle. In addition, given the dynamic nature of indexes, they have the potential to be updated in real-time as information becomes available.     

Effects of the Texel muscling quantitative trait locus on carcass traits in crossbred lambs

Texel muscling quantitative trait locus (TM-QTL) is a QTL on chromosome 18, originally identified in purebred UK Texel sheep, which was reported to increase ultrasonically measured muscle depth at the third lumbar vertebra by around 4% to 7%. The objective of the present study was to comprehensively evaluate the TM-QTL and to determine whether it could provide benefits to the UK sheep industry through increased carcass meat yield in crossbred slaughter lambs. Effects of this QTL on a range of carcass traits, including those measured in vivo and by dissection, were evaluated in heterozygous carrier and non-carrier lambs produced by crossing heterozygous carrier Texel rams with non-carrier Mule (Bluefaced Leicester × Scottish Blackface) ewes from a lowland flock. The TM-QTL was found to increase loin muscling in crossbred lambs at a given live weight or carcass weight, as measured by ultrasound, X-ray computed tomography (CT) and carcass dissection. Depth of M. longissimus lumborum (MLL) was greater in TM-QTL carrier lambs compared to non-carriers as measured by both ultrasound at the third lumbar vertebra (+4.5%; P = 0.033) and CT scanning at the fifth lumbar vertebra (+6.7%; P = 0.004). Width and area of MLL measured using CT were also greater in TM-QTL carrier lambs compared to non-carriers (+3.0%; P = 0.013 and +5.1%; P = 0.047, respectively). Loin muscle volume measured using CT was greater in TM-QTL carriers than in non-carriers (+5.9%; P = 0.005) and the dissected weight of the MLL was +7.1% greater in TM-QTL carriers compared to non-carriers (P < 0.001). The proportion of the total carcass lean meat yield (LMY) that was contained within the loin region was slightly higher in TM-QTL carriers than in non-carriers (0.154 v. 0.145; P = 0.006). However, TM-QTL was found to have no significant effect on the total weight or proportion of LMY or of saleable meat yield in the carcass measured by dissection, or on muscling in the hind leg measured by CT or dissection. This work has verified that the inheritance of TM-QTL is associated with increased loin muscling in crossbred lambs, as has previously been reported for purebred Texel lambs.     

From phenotyping towards breeding strategies: using in vivo indicator traits and genetic markers to improve meat quality in an endangered pig breed

In endangered and local pig breeds of small population sizes, production has to focus on alternative niche markets with an emphasis on specific product and meat quality traits to achieve economic competiveness. For designing breeding strategies on meat quality, an adequate performance testing scheme focussing on phenotyped selection candidates is required. For the endangered German pig breed ‘Bunte Bentheimer’ (BB), no breeding program has been designed until now, and no performance testing scheme has been implemented. For local breeds, mainly reared in small-scale production systems, a performance test based on in vivo indicator traits might be a promising alternative in order to increase genetic gain for meat quality traits. Hence, the main objective of this study was to design and evaluate breeding strategies for the improvement of meat quality within the BB breed using in vivo indicator traits and genetic markers. The in vivo indicator trait was backfat thickness measured by ultrasound (BF_iv), and genetic markers were allele variants at the ryanodine receptor 1 (RYR1) locus. In total, 1116 records of production and meat quality traits were collected, including 613 in vivo ultrasound measurements and 713 carcass and meat quality records. Additionally, 700 pigs were genotyped at the RYR1 locus. Data were used (1) to estimate genetic (co)variance components for production and meat quality traits, (2) to estimate allele substitution effects at the RYR1 locus using a selective genotyping approach and (3) to evaluate breeding strategies on meat quality by combining results from quantitative-genetic and molecular-genetic approaches. Heritability for the production trait BF_iv was 0.27, and 0.48 for backfat thickness measured on carcass. Estimated heritabilities for meat quality traits ranged from 0.14 for meat brightness to 0.78 for the intramuscular fat content (IMF). Genetic correlations between BF_iv and IMF were higher than estimates based on carcass backfat measurements (0.39 v. 0.25). The presence of the unfavorable n allele was associated with increased electric conductivity, paler meat and higher drip loss. The allele substitution effect on IMF was unfavorable, indicating lower IMF when the n allele is present. A breeding strategy including the phenotype (BF_iv) combined with genetic marker information at the RYR1 locus from the selection candidate, resulted in a 20% increase in accuracy and selection response when compared with a breeding strategy without genetic marker information.     

The value of muscular and skeletal scores in the live animal and carcass classification scores as indicators of carcass composition in cattle

The objective was to determine the relationship of muscular and skeletal scores taken on the live animal and carcass conformation and fat scores with carcass composition and value. Bulls (n = 48) and heifers (n = 37) of 0.75 to 1.0 late-maturing breed genotypes slaughtered at 16 and 20 months of age, respectively, were used. At 8 months of age (weaning) and immediately pre-slaughter, visual muscular scores were recorded for each animal and additionally skeletal scores were recorded pre-slaughter. Carcass weight, kidney and channel fat weight, carcass conformation and fat scores, fat depth over the longissimus dorsi muscle at the 12th (bulls) or 10th (heifers) rib and carcass length were recorded post-slaughter. Each carcass was subsequently dissected into meat, fat and bone using a commercial dissection procedure. Muscular scores taken pre-slaughter showed positive correlations with killing-out rate (r ≈ 0.65), carcass meat proportion (r ≈ 0.60), value (r ≈ 0.55) and conformation score (r ≈ 0.70), and negative correlations with carcass bone (r ≈ -0.60) and fat (r ≈ -0.4) proportions. Corresponding correlations with muscular scores at weaning were lower. Correlations of skeletal scores taken pre-slaughter, carcass length and carcass weight with killing-out rate and the various carcass traits were mainly not significant. Carcass fat depth and kidney and channel fat weight were negatively correlated with carcass meat proportion and value, and positively correlated with fat proportion. Correlations of carcass conformation score were positive (r = 0.50 to 0.68) with killing-out rate, carcass meat proportion and carcass value and negative with bone (r ≈ -0.56) and fat (r ≈ -0.40) proportions. Corresponding correlations with carcass fat score were mainly negative except for carcass fat proportion (r ≈ 0.79). A one-unit (scale 1 to 15) increase in carcass conformation score increased carcass meat proportion by 8.9 and 8.1 g/kg, decreased fat proportion by 4.0 and 2.9 g/kg and decreased bone proportion by 4.9 and 5.2 g/kg in bulls and heifers, respectively. Corresponding values per unit increase in carcass fat score were -11.9 and -9.7 g/kg, 12.4 and 9.9 g/kg, and -0.5 and -0.2 g/kg. Carcass conformation and fat scores explained 0.70 and 0.55 of the total variation in meat yield for bulls and heifers, respectively. It is concluded that live animal muscular scores, and carcass conformation and fat scores, are useful indicators of carcass meat proportion and value.     

Predicting beef carcass meat,fat and bone proportions from carcass conformation and fat scores or hindquarter dissection

Equations for predicting the meat, fat and bone proportions in beef carcasses using the European Union carcass classification scores for conformation and fatness, and hindquarter composition were developed and their accuracy was tested using data from 662 cattle. The animals included bulls, steers and heifers, and comprised of Holstein–Friesian, early- and late-maturing breeds × Holstein–Friesian, early-maturing × early-maturing, late-maturing × early-maturing and genotypes with 0.75 or greater late-maturing ancestry. Bulls, heifers and steers were slaughtered at 15, 20 and 24 months of age, respectively. The diet offered before slaughter includes grass silage only, grass or maize silage plus supplementary concentrates, or concentrates offered ad libitum plus 1 kg of roughage dry matter per head daily. Following the slaughter, carcasses were classified mechanically for conformation and fatness (scale 1 to 15), and the right side of each carcass was dissected into meat, fat and bone. Carcass conformation score ranged from 4.7 to 14.4, 5.4 to 10.9 and 2.0 to 12.0 for bulls, heifers and steers, respectively; the corresponding ranges for fat score were 2.7 to 11.5, 3.2 to 11.3 and 2.8 to 13.3. Prediction equations for carcass meat, fat and bone proportions were developed using multiple regression, with carcass conformation and fat score both included as continuous independent variables. In a separate series of analyses, the independent variable in the model was the proportion of the trait under investigation (meat, fat or bone) in the hindquarter. In both analyses, interactions between the independent variables and gender were tested. The predictive ability of the developed equations was assed using cross-validation on all 662 animals. Carcass classification scores accounted for 0.73, 0.67 and 0.71 of the total variation in carcass meat, fat and bone proportions, respectively, across all 662 animals. The corresponding values using hindquarter meat, fat and bone in the model were 0.93, 0.87 and 0.89, respectively. The bias of the prediction equations when applied across all animals was not different from zero, but bias did exist among some of the genotypes of animals present. In conclusion, carcass classification scores and hindquarter composition are accurate and efficient predictors of carcass meat, fat and bone proportions.     

Prediction of effects of beef selection indexes on greenhouse gas emissions

Genetic improvement in production efficiency traits can also drive reduction in greenhouse gas emissions. This study used international ‘best-practice’ methodology to quantify the improvements in system-wide CO₂ equivalent emissions per unit of genetic progress in the Irish Maternal Replacement (MR) and Terminal (T) beef cattle indexes. Effects of each index trait on system gross emissions (GE) and system emissions intensity (EI) were modelled by estimating effects of trait changes on per-animal feed consumption and associated methane production, per-animal meat production and numbers of animals in the system. Trait responses to index selection were predicted from linear regression of individual bull estimated breeding values for each index trait on their MR or T index value, and the resulting regression coefficients were used to calculate trait-wise responses in GE and EI from index selection. Summed over all trait responses, the MR index was predicted to reduce system GE by 0.810 kg CO₂e/breeding cow per year per € index and system EI by 0.009 kg CO₂e/kg meat per breeding cow per year per € index. These reductions were mainly driven by improvements in cow survival, reduced mature cow maintenance feed requirements, shorter calving interval and reduced offspring mortality. The T index was predicted to reduce system EI by 0.021 kg CO₂e/kg meat per breeding cow per year per € index, driven by increased meat production from improvements in carcass weight, conformation and fat. Implications for incorporating an EI reduction index to the current production indexes and long-term projections for national breeding programs are discussed.     

A preference-based approach to deriving breeding objectives: applied to sheep breeding

Using internet-based software known as 1000Minds, choice-experiment surveys were administered to experts and farmers from the Irish sheep industry to capture their preferences with respect to the relative importance - represented by part-worth utilities - of target traits in the definition of a breeding objective for sheep in Ireland. Sheep production in Ireland can be broadly separated into lowland and hill farming systems; therefore, each expert was asked to answer the survey first as if he or she were a lowland farmer and second as a hill farmer. In addition to the experts, a group of lowland and a group of hill farmers were surveyed to assess whether, and to what extent, the groups' preferences differ from the experts' preferences. The part-worth utilities obtained from the surveys were converted into relative economic value terms per unit change in each trait. These measures - referred to as 'preference economic values' (pEVs) - were compared with economic values for the traits obtained from bio-economic models. The traits 'value per lamb at the meat processor' and 'lamb survival to slaughter' were revealed as being the two most important traits for the surveyed experts responding as lowland and hill farmers, respectively. In contrast, 'number of foot baths per year for ewes' and 'number of anthelmintic treatments per year for ewes' were the two least important traits. With the exception of 'carcase fat class' (P < 0.05), there were no statistically significant differences in the mean pEVs obtained from the surveyed experts under both the lowland and hill farming scenarios. Compared with the economic values obtained from bio-economic models, the pEVs for 'lambing difficulty' when the experts responded as lowland farmers were higher (P < 0.001); and they were lower (P < 0.001) for 'carcase conformation class', 'carcase fat class' (less negative) and 'ewe mature weight' (less negative) under both scenarios. Compared with surveyed experts, pEVs from lowland farmers differed significantly for 'lambing difficulty', 'lamb survival to slaughter', 'average days to slaughter of lambs', 'number of foot baths per year for ewes', 'number of anthelmintic treatments per year for ewes' and 'ewe mature weight'. Compared with surveyed experts, pEVs from hill farmers differed significantly for 'lambing difficulty', 'average days to slaughter of lambs' and 'number of foot baths per year for ewes'. This study indicates that preference-based tools have the potential to contribute to the definition of breeding objectives where production and price data are not available.     

The levels of artificial insemination and missing sire information make genomic selection not always beneficial in meat sheep

Numerous meat sheep breeding programs in developed and developing countries are characterized by incomplete sire information and a predominant use of natural matings. These two parameters potentially affect the benefit of genomic selection (GS), especially for the selection of a late-in-life trait. Using stochastic simulations, the genetic gains obtained using genomic and conventional strategies for a maternal trait were evaluated in meat sheep population. Natural mating and artificial insemination (AI)-based designs, inspired by the current diversity of designs used for French meat sheep breeds, were modeled and three genomic strategies were tested and compared with a conventional selection strategy: parentage assignment, GS based on a male or a male and female reference population. Genomic selection based on a male reference population did not always outperform conventional selection. Its benefit depended on the design, the level of missing information on dam sires, and the level of AI. Genomic selection based on a male and female reference population always outperformed the conventional selection strategy, even if only 25 % of the females in the nucleus were genotyped.     

Breeding objectives for sheep should be customised depending on variation in pasture growth across years

Breeding programmes for livestock require economic weights for traits that reflect the most profitable animal in a given production system, which affect the response in each trait after selection. The profitability of sheep production systems is affected by changes in pasture growth as well as grain, meat and wool prices between seasons and across years. Annual pasture growth varies between regions within Australia’s Mediterranean climate zone from low growth with long periods of drought to high growth with shorter periods of drought. Therefore, the objective of this study was to assess whether breeding objectives need to be adapted for regions, depending on how reliable the pasture growth is across years. We modelled farms with Merino sheep bred for wool and meat in 10 regions in Western Australia. Across these 10 regions, mean annual pasture growth decreased, and the CV of annual pasture growth increased as pasture growth for regions became less reliable. We calculated economic values for nine traits, optimising management across 11 years, including variation for pasture growth and wool, meat and grain prices between and within years from 2002 to 2012. These economic values were used to calculate responses to selection for each trait for the 10 regions. We identified two potential breeding objectives, one for regions with low or high reliability and the other for regions with medium reliability of pasture growth. Breeding objectives for high or low pasture growth reliability had more emphasis on live weight traits and number of lambs weaned. Breeding objectives for medium reliability of pasture growth had more emphasis on decreasing fibre diameter. Relative economic weights for fleece weight did not change across the regions. Regions with low or high pasture reliability had similar breeding objectives and response to selection, because the relationship between the economic values and CV of pasture growth were not linear for live weight traits and the number of lambs weaned. This non-linearity was caused by differences in distribution of pasture growth between regions, particularly during summer and autumn, when ewes were pregnant, with increases in energy requirements affecting the value of lambs weaned. In addition, increasing live weight increased the intake capacity of sheep, which meant that more poor quality pasture could be consumed during summer and autumn, which had more value in regions with low and high pasture reliability. We concluded that breeding values for sheep production systems should be customised depending on the reliability of pasture growth between years.     

新疆肉羊18号染色体上与后臀肌发育相关基因的多态性分析

通过对新疆肉羊18号染色体与后臀肌发育相关基因的多态性分析,试图找到与新疆肉羊后臀肌性状发达相关基因,为肉羊分子标记辅助选择提供理论线索。运用PCR-SSCP、PCR-RFLP方法,对陶赛特和萨福克两个肉羊品种群体及其与本地细毛羊杂交1代和2代群体Callipyge（CLPG）基因的多态性进行分析,结果表明：位于18号染色体内的DLK1和GTL2间的103849 bp处没有发现PCR-RFLP多态性,表明新疆肉羊后臀肌过度发育与CLPG基因无关。随后,实验进一步对18号染色体Meg3.9位点158520处进行PCR-SSCP分析,发现扩增片段存在着多态性;Meg3.9扩增片段多态性位点在肉羊群体中的基因型有AA、AB和AC,以AA型为主。其中AA、AB基因型与新疆肉羊后臀肌肉发达的表型无关（P>0.05）,AC基因型与新疆肉羊后臀肌肉发达的表型相关（P<0.05）。在陶赛特与本地细毛羊杂交1代群体中,AC基因型的屠体重和屠宰率与AA、AB基因型差异显著（P<0.05）,但三种基因型的各月龄体重没有差异(P>0.05)。通过以上分析可以推断,引起新疆肉用绵羊后臀肌过度发育的性状不是CLPG基因内9571-268.3位点突变导致,可能还存在其他基因或与其连锁的多个QTL的共同作用。     

Genome‐wide association analysis for growth,muscularity and meat quality in Piétrain pigs

Improvement in growth and meat quality is one of the main objectives in sire line pig breeding programmes. Mapping quantitative trait loci for these traits using experimental crosses and a linkage‐based approach has been performed frequently in the past. The Piétrain breed often was involved as a founder breed to establish the experimental crosses. This breed was selected for muscularity and leanness but shows relatively poor meat quality. It is frequently used as a sire line breed. With the advent of genome‐wide and dense SNP chips in pig genomic research, it is possible to also conduct genome‐wide association studies within the Piétrain breed. In this study, around 500 progeny‐tested sires were genotyped with 60k SNPs. Data filtering showed that around 48k SNPs were useable in this sample. These SNPs were used to conduct a genome‐wide association study for growth, muscularity and meat quality traits. Because it is known that a mutation in the RYR1 gene located on chromosome 6 shows a major effect on meat quality, this mutation was included in the models. Single‐marker and multimarker association analyses were performed. The results revealed between zero and eight significant associations per trait with P < 5 × 10^?5. Of special interest are SNPs located on SSC6, SSC10 and SSC15.     

The effects of a loin muscling quantitative trait locus (LoinMAX™) on carcass and VIA-based traits in crossbred lambs

LoinMAX (LM) is a quantitative trait locus (QTL), which was found to be segregated in Australian Poll Dorset sheep, and maps to the distal end of sheep chromosome 18. LM-QTL was reported to increase Musculus longissimus dorsi area and weight by 11% and 8%, respectively. The aim of this study was to comprehensively evaluate the direct effects of LM-QTL in a genetic background typical of the stratified structure of the UK sheep industry, before it can be recommended for use in the United Kingdom. Crossbred lambs, either non-carriers or carrying a single copy of LM-QTL, were produced out of Scottish Mule ewes (Bluefaced Leicester × Scottish Blackface) artificially inseminated with semen from two Poll Dorset rams that were heterozygous for LM-QTL. Unexpectedly, one of these rams was also heterozygous for a QTL that affects the overall carcass muscling (MyoMAX™). This was accounted for by nesting MyoMAX™ status (carrier or non-carrier) within sire in the statistical analysis. Lambs were weighed and scanned by using X-ray computed tomography (CT) at an average age of 113 days. Ultrasound scan measurements, along with lamb weights, were taken at an average age of 140 days and lambs were then slaughtered. Carcasses were weighed and classified for fat cover and conformation scores, based on the Meat and Livestock Commission (MLC) carcass classification scheme, and then scanned by using a video image analysis (VIA) system. M. longissimus lumborum (MLL) width, as measured by CT scanning, was greater (P < 0.05) in lambs heterozygous for LM-QTL compared with non-carriers. MLL in LM-QTL carrier lambs was also significantly deeper, as measured by both ultrasound muscle depth at the third lumbar vertebrae (+3.7%; P < 0.05) and CT scanning at the fifth lumbar vertebrae (+3.4%; P < 0.01). Consequently, MLL area, was measured by using CT scanning, was significantly higher (+4.5%; P < 0.01) in lambs carrying a single copy of LM-QTL compared with non-carriers. Additional traits measured by CT, such as leg muscle dimensions, average muscle density and tissue proportions, were not significantly affected by LM-QTL. LM-QTL did not significantly affect total carcass lean or fat weights or MLC conformation and fat score classifications. Using previously derived algorithms, VIA could detect a significant effect of the LM-QTL on the predicted weight of saleable meat yield in the loin primal cut (+2.2%; P < 0.05), but not in the other primal cuts, or the total carcass.     

The Boer goat. II. Growth, nutrient requirements, carcass and meat quality

Growth rates of Boer goats were generally lower than sheep and, under favorable nutritional conditions, weight gains of more than 200 g per day were obtained, against values of up to 176 g per day under extensive subtropical conditions. Lactation and pregnancy had a marked effect on ME intake, and the latter had an improved feed conversion ratio (6.06 kg/kg) in comparison to that of virgin does (10.96 kg/kg). Below 6% crude protein in the diet, feed intake is reduced and has negative effects on birth weights, growth and milk production. Little information is available on mineral requirements of goats. The carcass of Boer goats is generally leaner, less compact and has different carcass proportions than sheep. The relatively high collagen contents with lower solubility of Boer goat meat, has meant that the eating quality has been regarded as inferior to that of lamb and mutton. Breeding holds the key to improving tenderness of goat meat; different slaughtering techniques can be used as well. Boer goats have high potential as meat animals when yielding three kid crops in 2 years and when fed to gain more than 200 g/day.     

The relationship of live animal muscular and skeletal scores, ultrasound measurements and carcass classification scores with carcass composition and value in steers

This study examined the relationship of muscular and skeletal scores and ultrasound measurements in the live animal, and carcass conformation and fat scores with carcass composition and value using 336 steers, slaughtered at 2 years of age. Live animal scores and measurements were recorded at 8 to 12 months of age and pre-slaughter. Following slaughter, each carcass was classified for conformation and fatness and the right side dissected into meat, fat and bone. Carcass conformation scores and fat scores were both measured on a continuous 15-point scale and ranged from 2.0 to 12.0 and from 2.8 to 13.3, respectively. Pre-slaughter muscular scores showed positive correlations (P < 0.001) ranging from 0.31 to 0.86 with carcass meat proportion, proportion of high-value cuts in the carcass, conformation score and carcass value, significant negative correlations with carcass fat (r = -0.13) and bone (r = -0.81) proportions, and generally low non-significant relationships with the proportion of high-value cuts in meat and carcass fat score. Pre-slaughter ultrasound muscle depth and carcass conformation score showed similar correlations with carcass traits to those using the pre-slaughter muscular scoring procedure. Pre-slaughter ultrasound fat depth showed positive correlations (P < 0.001) with carcass fat proportion (r = 0.59) and fat score (r = 0.63), and significant negative correlations (-0.23 to -0.50) with carcass meat and bone proportions, high-value cuts in the carcass and in meat, and carcass value. Pre-slaughter skeletal scores generally showed poor correlations ranging from -0.38 to 0.52 with the various carcass traits. Corresponding correlations (-0.26 to 0.44) involving records collected at 8 to 12 months of age were lower than those using pre-slaughter records. A one-unit increase in carcass conformation score increased carcass meat proportion and value by 11.2 g/kg and 5.6 cents/kg, respectively. Corresponding values for fat score were -8.2 g/kg and -5.1 cents/kg. In conclusion, both pre-slaughter live animal scores/measurements and carcass classification scores, explained an appreciable amount of the total variation in carcass meat, fat and bone proportions and carcass value, and a moderate amount of the variation in proportion of high-value meat cuts in the carcass.     

Genetic parameters of Visual Image Analysis primal cut carcass traits of commercial prime beef slaughter animals

Visual Image analysis (VIA) of carcass traits provides the opportunity to estimate carcass primal cut yields on large numbers of slaughter animals. This allows carcases to be better differentiated and farmers to be paid based on the primal cut yields. It also creates more accurate genetic selection due to high volumes of data which enables breeders to breed cattle that better meet the abattoir specifications and market requirements. In order to implement genetic evaluations for VIA primal cut yields, genetic parameters must first be estimated and that was the aim of this study. Slaughter records from the UK prime slaughter population for VIA carcass traits was available from two processing plants. After edits, there were 17 765 VIA carcass records for six primal cut traits, carcass weight as well as the EUROP conformation and fat class grades. Heritability estimates after traits were adjusted for age ranged from 0.32 (0.03) for EUROP fat to 0.46 (0.03) for VIA Topside primal cut yield. Adjusting the VIA primal cut yields for carcass weight reduced the heritability estimates, with estimates of primal cut yields ranging from 0.23 (0.03) for Fillet to 0.29 (0.03) for Knuckle. Genetic correlations between VIA primal cut yields adjusted for carcass weight were very strong, ranging from 0.40 (0.06) between Fillet and Striploin to 0.92 (0.02) between Topside and Silverside. EUROP conformation was also positively correlated with the VIA primal cuts with genetic correlation estimates ranging from 0.59 to 0.84, whereas EUROP fat was estimated to have moderate negative correlations with primal cut yields, estimates ranged from −0.11 to −0.46. Based on these genetic parameter estimates, genetic evaluation of VIA primal cut yields can be undertaken to allow the UK beef industry to select carcases that better meet abattoir specification and market requirements.