Assessing beef carcass tissue weights using computed tomography spirals of primal cuts.

More than 800 beef primal cuts from 44 Aberdeen Angus and Limousin-cross steers carcasses were scanned using spiral computed tomography (CT) and dissected. Thresholds for the segmentation of fat, muscle and bone in the CT spirals were estimated with the objective of assessing the weight of these tissues in the primal cuts and in the entire carcasses. Thresholds were estimated using half of the dataset (DBE) and then validated in the other half (DBV). Automatic image analysis procedures were used to assess tissue weights. The R(2) of the regression between primal tissue weight by dissection and CT were high in both datasets for fat (DBE, 0.89; DBV, 0.92), muscle (DBE, 0.99; DBV, 0.99) and bone (DBE, 0.95; DBV, 0.97). The estimation of total carcass tissue weights were also very accurate for the three tissues (R(2) values of 0.95 to 0.96), indicating that CT scanning may deliver very accurate information on beef carcass composition faster and with lower cost than physical dissection and without damaging or depreciating the primal joints.

Predicting beef carcass composition using tissue weights of a primal cut assessed by computed tomography.

The potential of the composition of the forerib measured by X-ray computed tomography (CT) as a predictor of carcass composition was evaluated using data recorded on 30 Aberdeen Angus and 43 Limousin crossbred heifers and steers. The left sides of the carcasses were split into 20 cuts, which were CT scanned and fully dissected into fat, muscle and bone. Carcass and forerib tissue weights were assessed by dissection and CT. Carcass composition was assessed very accurately by CT scanning of the primal cuts (adj-R2 = 0.97 for the three tissues). CT scanning predicted weights of fat, muscle and bone of the forerib with adj-R2 of 0.95, 0.91 and 0.75, respectively. Single regression models with the weights of fat, muscle or bone in the forerib measured by CT as the only predictors to estimate fat, muscle or bone of the left carcass obtained by CT showed adjusted coefficients of determination (adj-R2) of 0.79, 0.60 and 0.52, respectively. By additionally fitting breed and sex, accuracy increased to 0.85, 0.73 and 0.67. Using carcass and forerib weights in addition to the previous predictors improved significantly the prediction accuracy of carcass fat and muscle weights to adj-R2 values of 0.92 and 0.96, respectively, while the highest value for carcass bone weight was 0.77. In general, equations derived using CT data had lower adj-R2 values for bone, but better accuracies for fat and muscle compared to those obtained using dissection. CT scanning could be considered as an alternative very accurate and fast method to assess beef carcass composition that could be very useful for breeding programmes and research studies involving a large number of animals, including the calibration of other indirect methods (e.g. in vivo and carcass video image analysis).

Muscle fibre characteristics of two contrasting sheep breeds: Scottish Blackface and Texel.

This study evaluates the effects of breed and sex, together with those of birth weight and litter size, on muscle fibre type characteristics in Texel (TEX) and Scottish Blackface sheep (SBF). The M.longissimus thoracis et lumborum (LTL) of TEX had a significantly higher total muscle cross-sectional area (16%), a higher total fibre number (20%) and a higher muscle CT density (5%) than the SBF but had a similar average muscle fibre size. The frequency of slow fibres in the LTL in TEX was lower than in SBF (7.5% vs. 9.6%). Muscle fibre histochemistry similarly demonstrated that the oxidative fibre frequency in TEX was 10% lower than in SBF. The inter-fibre lipid content in TEX was also significantly lower than in SBF. Correspondingly, TEX displayed higher frequency (91.7% vs. 90.9% in SBF) and higher relative total area (92.5% vs. 90.4% in SBF) of fast fibres. These breed differences in muscle fibre traits indicate underlying genetic variation, and future analyses will evaluate the link of these traits to meat quality and assess the usefulness of these traits in breeding programmes.

Prediction of lamb carcass composition and meat quality using combinations of post-mortem measurements.

Various post-mortem measurements (carcass weights, conformation and fatness classes, external carcass dimensions, eye muscle dimensions, subcutaneous fat depth, pH and temperature) were recorded on 197 Texel (TEX) and 200 Scottish Blackface (SBF) lamb carcasses. The potential use of these measurements to predict carcass composition and key meat quality traits was investigated, to enable categorisation of carcasses in the abattoir and/or for use in genetic improvement programmes. By combining different measurements, accurate predictions of dissected carcass muscle weight (adjusted R(2) 0.93 in TEX, 0.88 in SBF) and fat weight (adjusted R(2) 0.84 in TEX, 0.87 in SBF) were achieved, and moderate predictions of intra-muscular fat (adjusted R(2) 0.56 in TEX, 0.48 in SBF), whilst shear force was predicted with low to moderate accuracy (adjusted R(2)<0.33 across breeds and cuts). Sex, eye muscle dimensions and subcutaneous fat depth improved predictions of carcass composition and intra-muscular fat, whilst pH or temperature provided little additional benefit for these traits, but increased prediction accuracies for shear force. These results could contribute to the development of automated carcass grading systems or help inform breeding decisions.

Prediction of lamb meat eating quality in two divergent breeds using various live animal and carcass measurements.

This study investigated how accurately taste panel sensory assessments of meat eating quality (MEQ) could be predicted in two divergent lamb breeds, using predictors measured in live animals (weights, subjective conformation assessments, ultrasound, computed tomography (CT) and video image analysis measurements) and carcasses (weights, MLC fat and conformation classes, pH, temperature, carcass dimensions and cross-sectional tissue dimensions), individually and in optimal combinations. Grilled muscle samples from the pelvic limb (semimembranosus) and loin (Longissimus lumborum) of 120 Texel (TEX) and 112 Scottish Blackface (SBF) lambs were assessed by a trained taste panel for texture, juiciness, flavour, abnormal flavour and overall liking. Residual correlations (adjusted for fixed effects, age and sire) between MEQ and predictor traits were low to moderate in size (<±0.42). MEQ traits predicted best by single measurements were loin flavour and overall liking for TEX (using fat area in a CT scan or subcutaneous fat depth measured post-mortem), and for SBF were leg texture (using carcass weight or temperature) and juiciness (using CT fat area or shoulder conformation score). Combining live animal and carcass measurements increased MEQ prediction accuracies, compared with using either set alone, to explain >40% of residual variation in several MEQ traits, with the highest adjusted R(2) values for leg juiciness in TEX (0.53) and leg texture in SBF (0.59). The most useful predictors of MEQ depended on breed, with measurements of fatness generally more important in the lean breed and carcass size and muscling more important in the fatter breed.

Fat deposition, fatty acid composition and meat quality: A review.

This paper reviews the factors affecting the fatty acid composition of adipose tissue and muscle in pigs, sheep and cattle and shows that a major factor is the total amount of fat. The effects of fatty acid composition on meat quality are also reviewed. Pigs have high levels of polyunsaturated fatty acids (PUFA), including the long chain (C20-22) PUFA in adipose tissue and muscle. The full range of PUFA are also found in sheep adipose tissue and muscle whereas cattle 'conserve' long chain PUFA in muscle phospholipid. Linoleic acid (18:2n-6) is a major ingredient of feeds for all species. Its incorporation into adipose tissue and muscle in relation to the amount in the diet is greater than for other fatty acids. It is deposited in muscle phospholipid at a high level where it and its long chain products eg aracidonic acid (20:4n-6) compete well for insertion into phospholipid molecules. Its proportion in pig adipose tissue declines as fat deposition proceeds and is an index of fatness. The same inverse relationships are not seen in ruminant adipose tissue but in all species the proportion of 18:2n-6 declines in muscle as fat deposition increases. The main reason is that phospholipid, where 18:2n-6 is located, declines as a proportion of muscle lipid and the proportion of neutral lipid, with its higher content of saturated and monounsaturated fatty acids, increases. Oleic acid (18:1cis-9), formed from stearic acid (18:0) by the enzyme stearoyl Co-A desaturase, is a major component of neutral lipid and in ruminants the same enzyme forms conjugated linoleic acid (CLA), an important nutrient in human nutrition. Like 18:2n-6, α-linolenic acid (18:3n-3) is an essential fatty acid and is important to ruminants since it is the major fatty acid in grass. However it does not compete well for insertion into phospholipid compared with 18:2n-6 and its incorporation into adipose tissue and muscle is less efficient. Greater biohydrogenation of 18:3n-3 and a long rumen transit time for forage diets also limits the amount available for tissue uptake compared with 18:2n-6 from concentrate diets. A positive feature of grass feeding is that levels of the nutritionally important long chain n-3 PUFA are increased ie EPA (20:5n-3) and DHA (22:6n-3). Future research should focus on increasing n-3 PUFA proportions in lean carcasses and the use of biodiverse pastures and conservation processes which retain the benefits of fresh leafy grass offer opportunities to achieve this. The varying fatty acid compositions of adipose tissue and muscle have profound effects on meat quality. Fatty acid composition determines the firmness/oiliness of adipose tissue and the oxidative stability of muscle, which in turn affects flavour and muscle colour. Vitamin E is an essential nutrient, which stabilises PUFA and has a central role in meat quality, particularly in ruminants.

Muscularity and eating quality of lambs: Effects of breed, sex and selection of sires using muscularity measurements by computed tomography.

Differences in muscularity of the hind leg (HL) and lumbar region (LR) were investigated between sexes (ram vs ewe lambs), breeds (Scottish Blackface, SBF vs Texel, TEX) and progeny of high- and low-muscularity sires (HM, LM) (n=471). The influence of these factors on meat eating quality (MEQ) was also examined (n=229). TEX lambs had 16% greater muscularity than SBF in both regions, whilst differences between sire groups were 4%. Ewe lambs had slightly higher values of muscularity for the HL than rams, but values were similar for the LR. Meat from SBF lambs had higher tenderness, stronger lamb flavour and higher overall liking than TEX meat. Sex had a weak influence with ram lambs having a stronger abnormal flavour and lower overall liking in the LR only. No significant differences in MEQ were found between HM- and LM-sired lambs, suggesting that improvements in muscularity would not have unfavourable effects on MEQ.

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

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

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.

Regional variation in the hedonic evaluation of lamb meat from diverse production systems by consumers in six European countries.

This paper describes the responses of consumers in six European countries (Greece, Italy, Spain, France, Iceland and United Kingdom) tasting meat from twelve different local types of lambs produced in those same six countries. Animals represented 10 breeds and crossbreeds, three sexes, several diets composed of either milk, concentrates and various forages as main ingredients and different slaughter ages, from 1 and 12 months, and carcass weights, from 5.5 to 30.4kg. Tests were conducted by 36 volunteer families in each of the six countries involved in the study. Families were asked to roast the joints using their own cooking criteria, evaluating (from "dislike extremely" to "like extremely") flavour, tenderness, juiciness and overall liking. Also the cook was asked to rate the odour during cooking. Country and lamb type and their interaction were statistically significant for all the variables analysed. Results suggest a link between the assessments of a given lamb type and the consumers' culinary background, showing clear associations between country and lamb type preferences. It was possible to separate, independently of the country, different groups of families with similar preferences. Five family groups, which included 88 families (40.74%), had a clear Mediterranean origin and preferred types of lamb fed either milk or mainly concentrate diets. Seven family groups, which included 93 families (43.06%) with a clear northern origin, preferred types reared on grass or with grass included in the diet. The rest of the groups (four) that included 35 families (16.20%) had no clear composition (northern or Mediterranean), and they had a wider taste preference. It can clearly be seen that there are two categories of consumers of lamb in the analysed European market: those who prefer "milk or concentrate taste" and those who prefer "grass taste".

Effect of breed, gender, housing system and dietary crude protein content on performance of finishing beef cattle fed maize-silage-based diets.

Maize silage-based diets with three dietary crude protein (CP) supplements were offered to 96 finishing cattle of contrasting breed (Holstein Friesian (HF) v. Simmental × HF (SHF)) and gender (bull v. steer) housed in two types of feeding system (group fed v. individually fed). The three protein supplements differed either in CP or protein degradability (degradable (LUDP) v. rumen undegradable (HUDP)) and provided CP concentrations of 142 (Con), 175 (LUDP) and 179 (HUDP) g/kg dry matter (DM) respectively, with ratios of degradable to undegradable of 3.0, 1.4 and 0.9:1 for diets Con, LUDP and HUDP, respectively. DM intakes were marginally higher (P = 0.102) for LUDP when compared with Con and HUDP. Rates of daily live-weight gain (DLWG) were higher (P = 0.005) in LUDP and HUDP when compared with Con. HF had higher DM intakes than SHF although this did not result in any improvement in HF DLWG. Bulls had significantly better DM intakes, DLWG and feed conversion efficiency than steers. Conformation scores were better in SHF than HF (P < 0.001) and fat scores lower in bulls than steers (P < 0.001). There was a number of first order interactions established between dietary treatment, breed, gender and housing system with respect to rates of gain and carcass fat scores.

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.

The relationship between body dimensions of living pigs and their carcass composition.

The performance of a visual image analysis (VIA) system was tested with regards to its potential to determine in vivo carcass composition and conformation, either alone, or in conjunction with other in vivo measures such as live weight and backfat depth. Pigs of both sexes of a commercial type were reared and slaughtered at weights ranging from 50 to 120 kg. Feeding was ad libitum on diets ranging from 0.14 to 0.19 kgkg(-1) crude protein content to produce animals of a range of body condition. Two analyses were carried out: the first analysis addressed the relationship between dimensionless carcass and VIA indices; the second analysis assessed the relationship between carcass composition and VIA body shape using detrended carcass and VIA data, which were produced by removal of allometric growth trends. A statistically significant relationship (P<0.05) between in vivo VIA body size and shape and carcass muscle dimensions and composition was found for most body regions. Adjusted R(2) statistics ranged between 0.13 and 0.54 for relative fat weights and between 0.14 and 0.51 for relative lean weights. The predictive power of the regression models, indicated by R(2)-like statistics for prediction, was approximately 70% of the adjusted R(2) values. The descriptive and predictive powers of the corresponding models generally strengthened if VIA indices were combined with other in vivo measurements. The relationships between in vivo and carcass measures remained statistically significant (P<0.05) after removal of the growth trends, although adjusted R(2) statistics generally decreased. The predictive power of models corresponding to the detrended measures was, however, weak. The results show in vivo VIA measurements to be useful in the estimation of muscle size, carcass conformation and composition, all of which are of significant importance to the pig production, marketing and processing industries.

Transfer of spinal cord material to subsequent bovine carcasses at splitting.

During the slaughter process, cattle carcasses are split by sawing centrally down the vertebral column, resulting in contamination of each half with spinal cord material. Using a novel method based on a real-time PCR assay, we measured saw-mediated tissue transfer among carcasses. Up to 2.5% of the tissue recovered from each of the five subsequent carcasses by swabbing the split vertebral face came from the first carcass to be split; approximately 9 mg was spinal cord tissue. Under controlled conditions in an experimental abattoir, between 23 and 135 g of tissue accumulated in the saw after splitting five to eight carcasses. Of the total tissue recovered, between 10 and 15% originated from the first carcass, and between 7 and 61 mg was spinal cord tissue from the first carcass. At commercial plants in the United Kingdom, between 6 and 101 g of tissue was recovered from the saw, depending on the particular saw-washing procedure and number of carcasses processed. Therefore, if a carcass infected with bovine spongiform encephalopathy were to enter the slaughter line, the main risk of subsequent carcass contamination would come from the tissue debris that accumulates in the splitting saw. This work highlights the importance of effective saw cleaning and indicates that design modifications are required to minimize the accumulation of spinal cord tissue debris and, hence, the risk of cross-contamination of carcasses.

Effects of fatty acids on meat quality: a review.

Interest in meat fatty acid composition stems mainly from the need to find ways to produce healthier meat, i.e. with a higher ratio of polyunsaturated (PUFA) to saturated fatty acids and a more favourable balance between n-6 and n-3 PUFA. In pigs, the drive has been to increase n-3 PUFA in meat and this can be achieved by feeding sources such as linseed in the diet. Only when concentrations of α-linolenic acid (18:3) approach 3% of neutral lipids or phospholipids are there any adverse effects on meat quality, defined in terms of shelf life (lipid and myoglobin oxidation) and flavour. Ruminant meats are a relatively good source of n-3 PUFA due to the presence of 18:3 in grass. Further increases can be achieved with animals fed grain-based diets by including whole linseed or linseed oil, especially if this is "protected" from rumen biohydrogenation. Long-chain (C20-C22) n-3 PUFA are synthesised from 18:3 in the animal although docosahexaenoic acid (DHA, 22:6) is not increased when diets are supplemented with 18:3. DHA can be increased by feeding sources such as fish oil although too-high levels cause adverse flavour and colour changes. Grass-fed beef and lamb have naturally high levels of 18:3 and long chain n-3 PUFA. These impact on flavour to produce a 'grass fed' taste in which other components of grass are also involved. Grazing also provides antioxidants including vitamin E which maintain PUFA levels in meat and prevent quality deterioration during processing and display. In pork, beef and lamb the melting point of lipid and the firmness/hardness of carcass fat is closely related to the concentration of stearic acid (18:0).

Growth of carcass components and its relation with conformation in pigs of three types.

The growth of carcass tissues and developmental changes in tissue distribution were studied in three pig types which were selected to have morphologies that could be described as attenuated, blocky and flabby. These were achieved by incorporating, respectively, Landrace, Pietrain and Meishan genes to give commercial 'types' (designated L, P and M,) exhibiting some of the phenotypic qualities of these breeds. Twenty-five female pigs of each type with an average start weight of 27.2 kg were fed ad libitum and slaughtered over a (nominal) live weight range of 35-115 kg. Relations were quantified using the logarithmic transformation of data in the allometric model. Significant type differences in relative growth rates (the b coefficient or slope in the logarithmic plot) were not common, occurring in 14% of the relationships examined, whereas 61% of differences in the constant term (a or intercept in the logarithmic plot) were significant. Increase in carcass weight with age was not different between the types but in relation to slaughter live weight (dressing percentage) P had the highest value, M the lowest. Carcass dimensions showed that, relative to body length, P had the widest ham and shoulder over the whole size range whereas M had a deep (ventral-dorsal) shoulder and wide belly, attributes of shape that would be regarded as undesirable by the meat trade. Relative to carcass weight, L was only slightly longer (3 mm) in the body than M at the heavy end of the weight range but markedly longer (29 mm) than P. These differences in carcass conformation were also evident in the shape of pelvic limb muscles which, at a given length, were lightest and narrowest in M and, in some cases, heavier and wider in P than in L. Pelvic limb volume relative to limb length was greatest in P and least in M. Carcass composition (at a given prepared side weight) of P was characterized by low fat and high lean weights, and a high lean to bone ratio. Subcutaneous fat b was lowest in P, indicating that P was early maturing, but M carcasses had the most subcutaneous and intermuscular fat, also indicative of early maturing. There was, thus, no simple relation between maturity characteristics and carcass composition. M carcasses also had the greatest weight of skin. P had a light hindloin and heavy pelvic limb, M a heavy shoulder, hindloin and flank but a light pelvic limb; L had a light shoulder but a heavy foreloin. The distribution of individual tissues mirrored these differences in joint weights to a varying extent; in most cases the match (relatively heavy/light) was with a single tissue. These data, thus, indicated some pig type differences in tissue distribution and of particular significance was the relatively light lean mass in the pelvic limb of M. The results showed important differences in carcass quality between commercially available pig types differing in conformation.

Effects of dietary fat source and breed on the carcass composition, n-3 polyunsaturated fatty acid and conjugated linoleic acid content of sheep meat and adipose tissue.

Seventy-two 8-week-old ram lambs from three breeds, Suffolk, Soay and Friesland, were offered one of four diets based on dried grass and formulated to have a similar fatty acid content (60 g/kg DM) and containing: Megalac (high in 16 : 0, control; Volac Ltd, Royston, Herts., UK), whole linseed (18 : 3n-3), fish oil (20 : 5n-3 and 22 : 6n-3) or whole linseed plus fish oil. The lambs were slaughtered at approximately half of their mature live weight (43, 21 and 43 kg for Suffolk, Soay and Friesland lambs, respectively). Fish oil reduced DM intake and lamb live-weight gain (P<0.001), while DM intake, live-weight gain and subcutaneous fat content were highest in Suffolk and lowest in Soay lambs. Linseed feeding doubled the proportion (x100) of 18 : 3n-3 in the longissimus dorsi from 1.4 to 3.1 and in the subcutaneous adipose tissue from 1.2 to 2.6 (P<0.001). Suffolk and particularly Soay lambs contained higher proportions of 18 : 3n-3 than Friesland lambs in the longissimus dorsi, while in the adipose tissue, Suffolk lambs had the highest level. Feeding fish oil increased the muscle proportion (x100) of 20 : 5n-3 from 0.7 to 2.3 and 22 : 6n-3 from 0.3 to 0.8 (P<0.001). By contrast, the proportions of the longer-chain n-3 polyunsaturated fatty acids were similar across all three breeds. All three lipid supplements containing n-3 polyunsaturated fatty acids increased the content of muscle trans-18 : 1 relative to the control values, but conjugated linoleic acid (cis-9,trans-11-18 : 2) only increased in the muscle of lambs fed linseed. Feeding linseed or fish oil lowered the n-6 : n-3 ratio in sheep meat, but neither diet nor breed had much effect on the polyunsaturated fatty acid: saturated fatty acid ratio.

Relationships between beef carcass shape and muscle to bone ratio.

Relationships between muscularity and muscle to bone ratio were investigated for beef carcasses of several breeds and crosses, and three genders using data from Bristol and Alberta. Side dissection data in terms of muscle, fat and bone weights were used to calculate muscle to bone ratios (MtoB) and muscularity indexes (MUSC) for the whole side or for the region around the femur bone. Highly significant breed and gender effects on MtoB and MUSC were shown for both the Bristol and the Alberta data sets, but the group differences for MtoB were not the same as those for MUSC despite the fact that these two characteristics were closely correlated. For both sets of data, for example, MUSC values at a common muscle plus bone weight were significantly higher for carcasses of bulls than heifers, but similarly adjusted MtoB values were generally higher for carcasses of heifers than bulls. Differences among breed groups were mainly in a similar direction for MUSC and MtoB, but the size of the differences varied widely. For example, relative to the Friesian, the Jersey breed had a significantly higher MtoB but a significantly lower MUSC, and carcasses of double-muscled bulls had a femur-region MtoB that was 19.2% greater than that of a group of Shorthorn-cross carcasses, but a MUSC that was only 1.7% higher. These findings show that because of the inconsistent relationships between muscularity and muscle to bone ratio among different classes of beef carcasses, lean meat yield cannot always be predicted without bias if measures of carcass shape are used as indicators of muscle to bone ratio.

Manipulating the fatty acid composition of muscle and adipose tissue in beef cattle.

Enhancing the n-3 polyunsaturated fatty acid (PUFA) content of beef is important in view of the generally saturated nature of fatty acids in ruminant meats and the negative effect this can have on human health. This study examined the effects of different sources of dietary n-3 PUFA on the performance of steers and the fatty acid composition of m. longissimus thoracis muscle and associated subcutaneous adipose tissue. Animals were fed ad libitum on grass silage plus one of four concentrates (60:40 forage:concentrate on a DM basis) containing differing sources of lipid: Megalac (16:0), lightly bruised whole linseed (18:3n-3), fish oil (20:5n-3 and 22:6n-3) and a mixture of linseed and fish oil (1:1, on an oil basis). Diets were formulated so that total dietary oil intake was 6 %, approximately half of which was from the experimental test oil. Linseed feeding not only increased the levels of 18:3n-3 in muscle phospholipid from 9.5 to 19 mg/100 g muscle but also enhanced the synthesis of 20:5n-3, the level of which increased from 10 to 15 mg/100 g muscle. Linseed also increased the proportion of 18:3n-3 in muscle neutral lipid and in adipose tissue lipids by a factor of 1.64 and 1.75 respectively. Fish oil feeding doubled the proportion of 20:5n-3 and 22:6n-3 in muscle phospholipids. The proportion of 18:1 trans in muscle neutral lipid was higher on the n-3 PUFA diets than the control diet, 0.04 and 0.02 respectively. Despite the implied modification to rumen metabolism, lipid source did not affect feed intake, growth rate, cold carcass weight or carcass fatness, but carcass conformation score was higher on fish oil treatments (P < 0.05). However, total muscle fatty acid content was not different between treatments and ranged from 3.5-4.3 % of tissue weight. The increase in n-3 PUFA in the meat produced by feeding linseed or fish oil lowered the n-6:n-3 ratio but had little effect on the P:S ratio.