Changes in connective tissue of M. semitendinosus as a response to different growth paths in steers

Dietary lecithin improves feed efficiency without impacting meat quality in immunocastrated male pigs and gilts fed a summer ration containing added fat

The aim of this study was to investigate the effects of sex and dietary lecithin on growth performance, meat quality, muscle collagen content and gene expression of key genes involved in collagen synthesis in finisher pigs. A total of 256 pigs (Large White × Landrace) were allotted to a 2 × 2 factorial arrangement involving sex (gilt or immunocastrated [IC] male) and dietary treatment (0 or 5 g/kg of dietary lecithin). All diets were formulated to contain 4.6% tallow with relatively high total fat of 6.3%. After 5 weeks of dietary treatment, pigs were slaughtered and Longissimus dorsi muscle was obtained for evaluation of meat quality and collagen content. Rectus abdominis muscle was analysed for gene expression of key genes involved in collagen synthesis namely, type I (α1) procollagen (COL1A1), type III (α1) procollagen (COL3A1), α-subunit of prolyl 4-hydroxylase (P4H), lysyl oxidase and metalloproteinase-1 (MMP-1). The results showed that lecithin improved feed efficiency of all pigs (P < 0.05) but it had no effect on feed intake, average daily gain and dressing percentage (P > 0.05). Lecithin also had no effect on meat compression, shear force, collagen content and gene expression (P > 0.05). Immunocastrated male had higher growth rate and increased COL1A1 expression than gilts. However, sex had no effect on fat depth at the P2 site (65 mm from the midline over the last rib), collagen content and expression of other genes (P > 0.05). In conclusion, lecithin improved feed efficiency in finishing pigs without impacting pork quality. Thus, inclusion of lecithin in diets containing high amount of tallow during the summer period could be beneficial.

Factors influencing beef eating quality 1. Effects of nutritional regimen and genotype on organoleptic properties and instrumental texture

An experiment was conducted to determine if growth rate, as affected by level of feeding, during a 10-or 20-week period prior to slaughter could influence the tenderness and palatability of beef from young (approx. 14 months old at the start of experiment) steers. Steers, comprising 18 Aberdeen Angus (AA), 18 Charolais (CH) and 18 Holstein (HO) purebreds, were allocated, within genotype, to one of three levels of feeding: (a) moderate ((M/M) 750 kJ metabolizable energy (ME) per day per kg M0·75), (b) high ((H/H) 1050 kJ ME per day per kg M0·75) both for 20 weeks; or (c) moderate for the first 10 weeks followed by high for the remaining 10 weeks (M/H). The steers were slaughtered at a fixed age (approx. 19 months old) and samples ofm. longissimus lumborum(from all three genotypes) m. vastus lateralis and m. biceps femoris (from AA and CH only) separated, vacuum packed and stored at 2ºC for both 7 and 14 days before freezing. These cuts were subsequently assessed by a 12 member taste panel and texture analysis performed using Volodkevitch-type jaws.

Growth rates during the final 10 weeks of the experimental period differed between dietary regimen (M/M = 0·87; M/H = 1·25; and H/H = 1·02 kg/day; s.e.d. = 0·08;P< 0·001). Steers offered the M/M level of feeding grew more slowly (0·97 kg/day) than those offered the M/H and H/H level of feeding (1·20 kg/day; s.e.d. = 0·06;P< 0·001) over the entire 20 week experimental period. In spite of these differences in growth rate, there were no consistent effects on beef tenderness and general palatability. Mean growth rates for CH, HO and AA steers were 1·21, 1·13 and 1·03 kg/day (s.e.d. = 0·06;P< 0·05). Beef samples from AA steers consistently scored better for various sensory attributes than those from CH and HO steers; this may have been due, in part, to level of carcass fatness and rate of carcass cooling post mortem. Accounting for factors such as genotype within the experimental design and slaughtering animals at a relatively constant age reduced the variance associated with each sensory attribute to 0·6 of that observed in commercial practice. The data suggest that there is little opportunity to improve beef eating quality by increasing growth rate by dietary means in steers provided that moderate levels of gain (equivalent to the UK average) are maintained.

Factors influencing beef eating quality 2. Effects of nutritional regimen and genotype on muscle fibre characteristics

Eighteen purebred steers of three genotypes, Aberdeen Angus (AA), Charolais (CH) and Holstein (HO), were divided within genotype into three groups of six animals and offered one of three different levels of feeding either moderate (M/M) or high (H/H) both for 20 weeks or moderate for the first 10 weeks followed by high for the remaining 10 weeks (M/H). Growth rates during the final 10 weeks of the experimental period differed between dietary regimen (M/M = 0·87; M/H = 1·25; and H/H = 1·02 kg/day; s.e.d. = 0·08;P< 0·001). Over the entire 20 week experimental period animals offered the M/M level of feeding grew more slowly (0·97 kg/day) than those offered the M/H and H/H level of feeding (1·20 kg/day; s.e.d. = 0·06;P< 0·001). Mean growth rates for CH, HO and AA steers were 1·21, 1·13 and 1·03 kg/day (s.e.d. = 0·06;P< 0·05). The animals were all slaughtered at a fixed age of 18 months, according to the Meat and Livestock Commission Blueprint for beef and, 48 h post mortem, samples of m. longissimus lumborum (LL) and m. vastus lateralis (VL) were removed for analyses.

Muscle fibres were classified histochemically, according to their contractile and metabolic properties, and muscle fibre size was measured. Fibre type frequency was calculated and, in LL, the total fibre number of the muscle was estimated. There was little impact of feeding level, or consequentially growth rate, on muscle fibre frequency and size. The effects seen were confined mainly to LL where there were significant differences between the M/M and H/ H groups with respect to fast twitch glycolytic fibres (mean % frequency (M/M = 40·1 and H/H = 44·3; s.e.d. = 1·4;P< 0·01); mean % area (M/M = 51·9 and H/H 56·0; s.e.d. = 1·5;P< 0·05)) and apparent total fibre number (M/ M = 35·0; and H/H = 41·9 ✕ 104; s.e.d. = 1·7;P< 0·05) which were greater in H/H than in M/M groups. However, in both LL and VL the predominant differences were related to genotype; in particular, overall fibre size was smallest in CH, while slow oxidative (SO; type I) fibre area was highest in AA. For LL, analysis across all animals showed a positive relationship between SO area, % area, % frequency and overall acceptability of meat at 14 days as evaluated by a trained sensory panel. No such relationship was observed for VL. The data suggest that in this study manipulation of feeding level has only a small impact on muscle fibre characteristics and that the differences between genotype and muscle type may be more important in determining the variability of overall acceptability than growth rate.

Postweaning substitution of grazed forage with a high-energy concentrate has variable long-term effects on subcutaneous fat and marbling in Bos taurus genotypes

The objective of this study was to quantify the effects and interactions of stage of growth and genotype on commercial carcass traits and intramuscular fat (IMF) content in 5 muscles of steers ( = 165) and to test the hypothesis that substituting pasture with a high-energy concentrate during the immediate postweaning period increases IMF. Cattle of 3 genotypes (Angus, Hereford, and Wagyu × Angus; = 55/genotype) were selected at weaning from commercial herds, targeting genotypic differences in marbling and subcutaneous fatness. Following weaning, steers were fed for 168 d within 2 different improved, temperate pasture-based nutritional systems: a forage-only system (FS) and forage with high-energy supplemented system (SS), with 2 replicates per system. The supplement was fed at a level of 1% of average BW adjusted every 2 wk to provide an estimated 50% of energy requirements for 168 d from weaning. Pasture on offer in both systems was managed to match the BW of the FS and SS steers during the postweaning treatment period to avoid confounding due to differences in growth rate during this period. Steers were then regrouped into 2 replicates and backgrounded on improved, temperate pasture for 158 d and then grain fed within 1 group for 105 d (short fed) or 259 d (long fed). Groups were slaughtered at commencement (d 0) and end of postweaning nutritional treatments (d 168), end of backgrounding (d 326), and after short (d 431) or long feedlotting (d 585). Serial slaughter stage had an effect on all traits assessed ( < 0.01). The FS steers had more rib fat ( < 0.01) and higher Meat Standards Australia marbling score ( < 0.05) and a tendency ( < 0.10) to have greater eye muscle area than the SS steers throughout the study. Genotypic differences were evident ( < 0.05) for all traits assessed except HCW, dressing percentage, rib fat depth, ossification score, ultimate pH, and IMF in the semitendinosus muscle. The results for marbling and IMF do not support the use of a high-energy feed as a substitute for an equivalent amount of energy from pasture during the immediate postweaning period to enhance development of marbling.

Effects of backgrounding and finishing growth rates on P8 fat and intramuscular fat in Bos taurus steers

The present study investigates the effects of backgrounding and finishing growth rates of Bos taurus steers grown out on three post-weaning growth pathways, across 4 years (1995–1998) on fat deposition. Scanned P8 fat at backgrounding exit (SP8exit), scanned P8 fat before slaughter (SP8sla) and carcass intramuscular fat (IMF, %) were evaluated. Four equations to predict SP8sla and four equations to predict carcass IMF across years were developed. Three post-weaning growth pathways (GPs) generated by different nutritional treatments across years were used in the study. Growth pathways were created by backgrounding steers on pasture with no supplementation (GP1), pasture plus supplementary feeding formulated pellets (GP2) or pasture with access to a forage crop (GP3). The steers were then finished in a feedlot or on pasture to slaughter weights of 520 kg (Korean market specification) or 600 kg (Japanese market specification). Cubic smoothing splines were fitted to the liveweight of all animals from the start of backgrounding until slaughter. Backgrounding growth rates were interpolated off the GP curves and the mean average daily gain (ADG, kg/day) at Day 100 (D100, Days 100–91 before relocation to the finishing phase), and Day 150 (D150, Days 150–141 before relocation to the finishing phase) were calculated. Significant (P < 0.01) differences between SP8exit and backgrounding ADG (BADG) were detected in all years except GP2 v. GP3 in 1997. GP1 steers had the lowest BADG across all years, ranging from 0.39 to 0.88 kg/day. At backgrounding exit, the mean SP8exit for the different GPs was ranked, with GP1 < GP3 for all years, with significant (P < 0.01) differences among GP1, GP2 and GP3 in all years except 1996. At the end of finishing, the mean carcass IMF over all years and finish (pasture and feedlot) (P < 0.05) was 4.71% for GP1 v. 5.09% for GP3 for Korean market steers and the mean SP8sla (P < 0.01) was 14.59 mm for GP1 v. 16.04 mm for GP3 and the mean carcass IMF (P < 0.01) was 5.54% for GP1 v. 6.27% for GP3 for Japanese market steers. The residual correlation of the multivariate response variables, namely, D100, D150 and BADG v. SP8exit (n = 1054), SP8sla (n = 1049) and carcass IMF (n = 1002), indicated that the highest correlations, all significant (P < 0.01), were 0.33, 0.20 and 0.12 for BADG v. SP8exit, SP8sla and carcass IMF, respectively. The residual variances (mm2) of the four SP8sla equations were 6.14, 7.44, 8.72 and 10.73 for 1995, 1996, 1997 and 1998, respectively, and the residual variances (%2) for the four carcass IMF equations were 2.51, 2.26, 1.75 and 0.84, for 1995, 1996, 1997 and 1998, respectively.

Meat Science and Muscle Biology Symposium: manipulating meat tenderness by increasing the turnover of intramuscular connective tissue

Controlled reduction of the connective tissue contribution to cooked meat toughness is an objective that would have considerable financial impact in terms of added product value. The amount of intramuscular connective tissue in a muscle appears connected to its in vivo function, so reduction of the overall connective tissue content is not thought to be a viable target. However, manipulation of the state of maturity of the collagenous component is a biologically viable target; by increasing connective tissue turnover, less mature structures can be produced that are functional in vivo but more easily broken down on cooking at temperatures above 60°C, thus improving cooked meat tenderness. Recent work using cell culture models of fibroblasts derived from muscle and myoblasts has identified a range of factors that alter the activity of the principal enzymes responsible for connective tissue turnover, the matrix metalloproteinases (MMP). Fibroblasts cultured from 3 different skeletal muscles from the same animal show different cell proliferation and MMP activity, which may relate to the different connective tissue content and architecture in functionally different muscles. Expression of MMP by fibroblasts is increased by vitamins that can counter the negative effects of oxidative stress on new collagen synthesis. Preliminary work using in situ zymography of myotubes in culture also indicates increased MMP activity in the presence of epinephrine and reactive oxidative species. Comparison of the relative changes in MMP expression from muscle cells vs. fibroblasts shows that myoblasts are more responsive to a range of stimuli. Muscle cells are likely to produce more of the total MMP in muscle tissue as a whole, and the expression of latent forms of the enzymes (i.e., pro-MMP) may vary between oxidative and glycolytic muscle fibers within the same muscle. The implication is that the different muscle fiber composition of different muscles eaten as meat may influence the potential for manipulation of their connective tissue turnover.

Quality of lamb meat from the Information Nucleus Flock

The effects of production and processing factors on tenderness, and colour of lamb meat produced from 7 locations as part of the Australian Sheep Industry CRC’s Information Nucleus flock were investigated, using data from 2052 lambs slaughtered in 2007. At 24 h post-slaughter, samples of m. longissimus lumborum (LL) and m. semimembranosus (SM) were collected for measurement of intramuscular fat (IMF), myoglobin, iron and copper and fresh meat colour (L*, a*, b*) and pH at 24 h measured on the LL. pH and temperature measurements made pre-rigor were used to calculate the pH at 18°C. Tenderness was measured by LL shear force at days 1 (SF1) and 5 (SF5) post-slaughter, the shear force difference (SF-diff) and SM compression and collagen concentration were determined. Retail colour stability was assessed using over-wrapped LL under simulated retail display for 3 days, according to the change in the oxymyoglobin/metmyoglobin ratio. All traits were affected by flock and date of slaughter (P < 0.001). After 4 days of ageing, 70–95% of the LL samples from all flocks, except for one, had acceptable tenderness for consumers based on their shear force. Low IMF, high LL pH at 18°C and high pH at 24 h increased SF1 and SF5 and also had an effect on SF-diff (P < 0.001). The retail colour of 44.8% of the samples on day 3 of retail display were lower than acceptable. Retail colour was influenced by IMF, pH18 and the concentration of iron and copper (P < 0.001). In conclusion, breeding and management practices that increase muscle IMF levels and reduce ultimate pH values and processing practices that result in moderate rates of pH fall post-slaughter, improve the tenderness of lamb. Extension of retail colour stability may be antagonistic to traits associated with tenderness and nutritional traits, particularly IMF and mineral levels.

Brahman and Brahman crossbred cattle grown on pasture and in feedlots in subtropical and temperate Australia. 2. Meat quality and palatability

Market demand for a reliable supply of beef of consistently high eating quality led the Cooperative Research Centre for Cattle and Beef Industry (Meat Quality) to initiate a crossbreeding progeny test program to quantify objective and sensory meat quality differences between straightbred and first-cross Brahman cattle. Brahman, Belmont Red, Santa Gertrudis, Angus, Hereford, Shorthorn, Charolais and Limousin sires were mated to Brahman females over 3 years to produce 1346 steers and heifers in subtropical northern Australia. Calves were assigned within sire by age and weight to one of three market endpoints (domestic, Korean or Japanese), one of two finishing environments (subtropical or temperate) and one of two finishing diets (pasture or feedlot). Average carcass weights were 227, 288 and 327 kg for domestic, Korean and Japanese markets respectively. Only steers were finished for the Japanese market. The effects of sire breed, finishing regime, market endpoint and sex on sensory meat quality of four attributes score (CMQ4), ossification score and Warner-Bratzler shear force (SF), instron compression (IC), ultimate pH and percent cooking loss (CL) on the M. longissimus thoracis et lumborum (LT) and M. semitendinosus (ST) were determined. Straightbred Brahmans had the highest SFLT (5.39 ± 0.07; P < 0.001), ICLT (1.89 ± 0.02; P < 0.05) and CL in both muscles (P < 0.05). Straightbred Brahmans were the only genotype that failed to meet minimum CMQ4 grading standards (38.3; P < 0.001). Progeny with up to 75% Brahman content successfully met minimum objective and sensory meat quality consumer thresholds for tenderness (IC <2.2 kg, SF <5.0 kg; CMQ4 >46.5). There was little difference between crossbred progeny for most meat quality traits. All feedlot-finished animals were slaughtered at domestic, Korean and Japanese market weights by 24 months of age, with minimal differences in objective measures of meat quality between markets. The IC measures for all sire breeds were below 2.2 kg, indicating connective tissue toughness was not an important market consideration in feedlot-finished animals slaughtered by 24 months of age. Pasture finishing adversely affected all meat quality traits (P < 0.001) except CLST, with Korean and Japanese market animals having unacceptably tough SF, IC and CMQ4 measures. This was attributed to their older age at slaughter (31 and 36 months respectively), resulting from their seasonally interrupted growth path. While domestic animals slaughtered at 25 months of age off pasture had unacceptably high SF and IC, CMQ4 was acceptable. Subtropical feedlot animals had slightly more desirable (n.s.) SF and IC relative to temperate feedlot animals, whereas temperate feedlot animals had higher CMQ4 (P < 0.001). Genotype × environment interactions were not important.

Sire and growth-path effects on sheep meat production. 3. Fascicular structure of lamb loin muscle (m. longissimus lumborum) and the impact on eating quality

The effects of sire genetics and growth path on the fascicular structure (FS) of lamb loin muscle (m. longissimus lumborum; LL) and the consequences for eating quality were studied in progeny (n = 299) of 20 Poll Dorset sires and Merino ewes. Sires were selected on the basis of their Australian sheep breeding values (ASBV) for post-weaning growth (PWWT), loin eye muscle depth (PEMD) and subcutaneous fat (PFAT). Growth of lambs was varied by time of weaning (early or late) and by feeding level within weaning group, where lambs were either fully fed throughout or were feed restricted for 55 days then re-alimented to achieve liveweight of ~45 kg at slaughter. The FS variables were determined in differentially stained histological sections of LL by using automated image segmentation and circle geometry methodology and were defined as percentage connective tissue, perimysial seam thickness and fascicular width. Sire ASBV was not a significant covariate to measures of FS, despite ASBV-related effects on growth, carcass leanness and fatness. Independent of weaning time, faster growth was induced by re-alimentation of feed-restricted lambs, resulting in LL with less connective tissue as a percentage of cross-sectional area and larger fascicles than for fully fed peers. The direction of the perimysial seam thickness response varied with treatment and time of weaning. Rapid growth of re-alimented early weaned restricted lambs resulted in thinner seams than for fully fed peers, whereas the opposite response was observed in the late-weaned lamb contrast. This suggests that the weight and age of the lamb at the time of nutritional compromise and re-alimentation are important factors in determining the thickness of perimysial connective-tissue seams. Whilst the evidence confirms differential accretion of the myofibrillar and connective tissues and despite reports of positive effects on tenderness brought about by such changes, variation in structural measures was not associated with variation in either objective measures (compression) or sensory scores for tenderness of the loin muscle. The data from the present study support the tenet that rapid growth before slaughter, combined with appropriate sire genetics, will not compromise the physical characteristics and sensory qualities of the meat.

Effect of different post-weaning growth paths on long-term weight gain, carcass characteristics and eating quality of beef cattle

The effects of post-weaning nutrient restriction on growth, carcass characteristics and beef quality were determined. Belmont Red weaner steers (n = 100) were allocated to an initial slaughter group and 3 treatment groups of 120 days duration: rapid growth, slow growth and weight loss. The average daily gain of the groups were (mean ± s.e.): 0.81 ± 0.02, 0.29 ± 0.02 and –0.22 ± 0.01 kg/day, for the rapid growth, slow growth and weight loss groups, respectively. At the end of the treatment period, rapid growth steers had significantly (P<0.05) heavier carcasses, higher dressing percentages and greater bone mineral contents than those from the weight loss group. Steers from each group were realimented for 192 days at pasture. Average daily gains during this period were 0.39 ± 0.03, 0.52 ± 0.04 and 0.61 ± 0.05 kg/day for the rapid growth, slow growth and weight loss groups, respectively. Ten animals from the rapid growth group were then slaughtered to determine carcass characteristics. The remaining steers were finished at pasture for a further 409 days. During this period there was no significant difference in average daily gain between treatment groups. Steers from the rapid growth group had a significantly greater final weight (531 ± 16.8 kg) compared with weight loss steers (481 ± 14.0 kg). Carcass characteristics, eye muscle area, bone mineral content and objective measures of meat quality for the M. longissimus dorsi and M. semitendinosus did not differ significantly between groups. Shear peak force values for cooked M. longissimus dorsi samples were not significantly different between groups. Clipped meat quality scores for M. longissimus dorsi samples, as assessed by Meat Standards Australia, were not significantly different between treatment groups and indicated consumer acceptability. It was concluded that nutrient restriction in the immediate post-weaning period followed by pasture realimentation did not influence final carcass characteristics or beef quality.

Effects of sire genotype and plane of nutrition on fascicular structure of M. longissimus thoracis et lumborum and its effect on eating quality

The purpose of this study was to determine if estimated breeding value (EBV) of an animal’s sire and or the animal’s nutrition affected the structure of its M. longissimus thoracis et lumborum (LL) and, hence, the eating quality of meat derived from its carcass. Lambs were chosen based on the EBV of their sires in terms of post-weaning live weight (PWWT), post weaning fat at the C-site (PFAT), and post-weaning eye muscle depth (PEMD). Morphometric techniques were used to characterise muscle structure in terms of the distribution of intramuscular connective tissue; the variables together are called fascicular structure. Perimysial seam thickness and fascicular width were both influenced by sire estimated breeding values for PWWT, PFAT, and PEMD. Variation in fascicular structure was associated with an interaction between PEMD-EBV and PFAT-EBV of the sire. Fascicular width decreased with increased PEMD-EBV and increased with PFAT-EBV, but was not affected by PWWT-EBV. When the total seam thickness was adjusted to a common fascicular width, the lambs on a low plane of nutrition had relatively more intramuscular connective tissue than those on a high plane. The total seam thickness was negatively associated with PFAT-EBV and positively associated with PEMD-EBV. Warner Bratzler shear (WBS) peak force (PF) and initial yield were not associated with differences in sire EBV. The residual WBS shear force, peak force minus initial yield (PFIY), and compression values were negatively associated with nutrition but were positively associated with PWWT-EBV and PEMD-EBV of the sires. These latter 2 effects were moderated by nutrition. The data support the hypothesis that morphological characteristics of perimysium are genetically determined and nutritionally responsive. Variance in morphology accounted for some variance in the biophysical attributes of meat and may help explain why sheep with high muscling potential have tougher meat.