Impact of Heatwaves on the Physiology and Retail Meat Quality of Lambs

The experiment investigated the impact of heatwaves (HWs) on the physiology, postmortem muscle metabolism and meat quality of lambs. Seventy-two second-cross lambs (Poll Dorset × (Border Leicester × Merino)) were selected and exposed to either 1, 3 or 5 days of HWs or thermoneutal (TN) (28–38 °C and 40–60% relative humidity, RH; 18–21 °C, 40–55% RH) conditions in climate-controlled chambers. Lambs exposed to 1–5 days of a HW exhibited higher respiration rates (RRs), rectal temperatures (RTs), skin temperatures (STs) and heart rates (HRs) compared to lambs exposed to an equal duration of TN conditions. However, HWs had no significant effects on muscle metabolism (rate and extent of pH decline, muscle glycogen and lactate content) and meat quality (cooking loss and shear force). Similarly, there were limited impacts of 1–5 days of HW on the colour (L*, a*, b* and R630/580) and drip loss of the longissimus thoracis et lumborum (LTL) and semimembranosus (SM) muscles for 4 days’ overwrap retail display. Results suggest that short-duration HWs (1–5 days) had significant negative effects on animal physiology but had no effect on the muscle metabolism and meat quality.

Effect of slaughter age and post-mortem days on meat quality of longissimus and semimembranosus muscles of Boer goats

This study investigated the effects of age of animal and days post-mortem (PM) on meat quality of Boer goats. Twenty-four (24) wether Boer goats of two age groups (2YO group: 2 years old and 9MO: 6-9 months, with 12 animals/group) were slaughtered in a commercial processing plant. The pH@Temp18 was estimated to be above 6 in both age groups with higher (P < 0.01) values in 2YO goats. The PM storage for 14 days reduced the shear force in both age groups (P < 0.01). 2YO goat muscles (longissimus and semimembranosus) exhibited higher (P < 0.01) Thiobarbituric acid reactive substance values (TBARS), indicating increased lipid oxidation. Glycogen (P < 0.01) and lactate content (20 min post-slaughter) in longissimus of 9MO were lower compared to 2YO, and total muscle glycogen concentration was lower (P < 0.01) in both age groups below the threshold levels. Hence, as hypothesized, age and days PM proved to play crucial roles on Boer meat quality.

Understanding the action of muscle iron concentration on dark cutting: An important aspect affecting consumer confidence of purchasing meat

We investigated the association of muscle iron concentration, in addition to ultimate pH (pHU), on dark meat formation in sheep of different breeds fed forage-based diets. At 1 h simulated display, redness of meat (a*-value) increased (P < .0001) by about 3 units as the iron concentration increased from 10 to 22 mg/kg of meat, whereas the a*-value decreased by 2 units as pHU increased from 5.5 to 6.2 in fresh meat (P < .0001). After 90 days storage the corresponding responses were about 2 units increase for iron concentration and about 1 unit decrease for pHU, respectively. The results clearly show that increased muscle iron concentration was strongly associated with reduced dark cutting in fresh and stored meat evaluated at 1 h simulated display. We conclude that it may be desirable to measure iron concentration, along with pHU, for evaluation of the potential for carcasses to produce dark cutting meat, and for the meat to turn brown during display.

High Oxygen Modified Atmosphere Packaging Negatively Influences Consumer Acceptability Traits of Pork

Current trends in meat packaging have seen a shift from conventional overwrap to vacuum packing (VAC) and modified atmosphere packaging (MAP). The aim of this experiment was to investigate the effects of high oxygen MAP (HiOxMAP) of pork loins compared with vacuum packed (VAC) on eating quality and colour, after storage in simulated illuminated retail display conditions. Pork loins (n = 40) were cut and stored under two packaging methods (HiOxMAP, 80% O₂, 20% CO₂; VAC) for up to 14 days, with samples taken at various times for measurements. After 7 days of storage, HiOxMAP samples exhibited inferior consumer acceptability for tenderness, flavor, overall liking, quality and re-purchase intention as well as higher shear force and hardness, relative to VAC samples (p < 0.05 for all). Loins stored in HiOxMAP had higher lightness (L*), redness (a*) and yellowness (b*) values at 3 and 7 days, but lower ratio of oxymoglobin to metmyoglobin (oxy/met) values in the meat surface at 14 days of display, relative to VAC samples (p < 0.05 for all). The oxy/met ratio declined from 2.3 to 1.7 between days 3 and 14 of display in HiOxMAP samples (p < 0.05), whereas the ratio was similar and stayed relatively high for VAC samples. VAC samples produced consistently higher colour values (a*, b*, oxy/met) when left to bloom 30 min after removal from packaging (p < 0.05). Lipid oxidation values, measured using thiobarbituric acid reactive substances, in HiOxMAP pork loins, were higher at all time points compared to VAC during the 14 day storage period (p < 0.05). The use of vacuum packing for retail shelves, should be considered as the preferred option, over HiOxMAP.

Breed and Nutrition Effects on Meat Quality and Retail Color after Lamb Pre-Slaughter Stress

The main objective of this research was to investigate the interactions between breed, nutrition and pre-slaughter stress, and the potential impacts on the meat quality and retail color/shelf life of lamb meat. Forty-eight Merino and second cross (Merino × Border Leicester) × Poll Dorset lambs were allocated to 2 dietary treatments: low energy diet (LE; 7.8 MJ ME/kg and 12% CP) vs. high energy (HE; 11.8 MJ ME/kg and 12% CP). Samples of longissimus lumborum (LL), and rectus femoris (RF) were taken 15 min post-slaughter for glycogen and lactate determination. pH and temperature of muscle samples were recorded at 0.5, 1.5, 3, 4.5, 6, and 24 h post-mortem. Muscle LL samples from the same side were collected at 24 h post slaughter for tenderness, cooking loss and retail color assessment. For retail color stability, the selected portion of muscle LL was sliced to create a fresh surface, placed on a tray and over wrapped. Color measurements were made fresh (after a 30 min bloom at 4°C, d 1) and then on d 3 and 6 of display, using a Hunter lab spectrophotometer XE Plus. Second-cross lambs on HE had the highest muscle glycogen at slaughter for both LL and RF. For the RF, the pHu values were elevated in Merinos on both LE and HE diets and 2X on the LE diet. Only for 2X lamb was the HE diet sufficient to reduce the pHu. HE diet reduced blood lactate in 2X lambs and elevated in Merinos. Merinos produced tougher meat at 6 d post-slaughter, which was also reflected by higher cooking losses. Both breeds of lambs on the LE diet had longer color shelf-life (higher R630/580) than the lambs on the HE diets.

Genetic correlations between wool traits and meat quality traits in Merino sheep

Genetic correlations between 29 wool production and quality traits and 25 meat quality and nutritional value traits were estimated for Merino sheep from an Information Nucleus (IN). Genetic correlations among the meat quality and nutritional value traits are also reported. The IN comprised 8 flocks linked genetically and managed across a range of sheep production environments in Australia. The wool traits included over 5,000 yearling and 3,700 adult records for fleece weight, fiber diameter, staple length, staple strength, fiber diameter variation, scoured wool color, and visual scores for breech and body wrinkle. The meat quality traits were measured on samples from the and included over 1,200 records from progeny of over 170 sires for intramuscular fat (IMF), shear force of meat aged for 5 d (SF5), 24 h postmortem pH (pHLL; also measured in the , pHST), fresh and retail meat color and meat nutritional value traits such as iron and zinc levels, and long-chain omega-3 and omega-6 polyunsaturated fatty acid levels. Estimated heritabilities for IMF, SF5, pHLL, pHST, retail meat color lightness (), myoglobin, iron, zinc and across the range of long-chain fatty acids were 0.58 ± 0.11, 0.10 ± 0.09, 0.15 ± 0.07, 0.20 ± 0.10, 0.59 ± 0.15, 0.31 ± 0.09, 0.20 ± 0.09, 0.11 ± 0.09, and range of 0.00 (eicosapentaenoic, docosapentaenoic, and arachidonic acids) to 0.14 ± 0.07 (linoleic acid), respectively. The genetic correlations between the wool production and meat quality traits were low to negligible and indicate that wool breeding programs will have little or no effect on meat quality. There were moderately favorable genetic correlations between important yearling wool production traits and the omega-3 fatty acids that were reduced for corresponding adult wool production traits, but these correlations are unlikely to be important in wool/meat breeding programs because they have high SE, and the omega-3 traits have little or no genetic variance. Significant genetic correlations among the meat quality traits included IMF with SF5 (-0.76 ± 0.24), fresh meat color * (0.50 ± 0.18), and zinc (0.41 ± 0.19). Selection to increase IMF will improve meat tenderness and color which may address some of the issues with Merino meat quality. These estimated parameters allow Merino breeders to combine wool and meat objectives without compromising meat quality.

The influence of the level of ewe gestation nutrition and lamb finishing diet on long-chain polyunsaturated fat concentration, antioxidant and mineral status, and colour stability of meat

The influence of ewe gestation nutrition (EGN) and lamb finishing diet (LFD) on muscle essential fatty acid, antioxidant and mineral status and retail colour of meat in F1 progeny lambs were investigated. First-cross Border Leicester × Merino and Maternal–Coopworth Composite ewes (n = 938) were artificially inseminated to nine terminal sires. From this flock, 648 pregnant ewes were selected between Day 41 and Day 49 of pregnancy, producing 72 pregnant ewes from each sire for distribution across six condition-score (CS) groups. Each CS group was balanced for three sires of high, medium and low lean meat yield and ewe breed. Variation in EGN was achieved through pasture allocations and supplementation, to meet three CS (2.5, 3.0 and 3.5) targets at lambing. At lambing, management of EGN ceased and ewes and lambs were given access to similar pasture allocations. Lambs were weaned at 12 weeks of age and backgrounded on pasture before the random allocation from within each block of sire by CS treatment combination, to the following three different finishing diets: high energy–high protein (HEHP); high energy–moderate protein (HEMP) and moderate energy–high protein (MEHP). Moderate EGN (CS 3.0) increased (P < 0.02) muscle C22:6n-3 and decreased (P < 0.04) C20:4n-6 concentrations compared with CS 2.5 and CS 3.5 EGN groups respectively. Redness of meat over the display period was greater (P = 0.005) for CS 3.0 and CS 3.5 EGN regimes than for the CS 2.5 regime. The MEHP diet reduced (P < 0.01) muscle C18:2n-6, C20:4n-6 and total n-6 fatty acid and increased antioxidant (vitamin E, P < 0.01) concentrations compared with HEHP and HEMP diets, but iron concentration was not affected. Differences in dietary vitamin E concentration between MEHP diet and HEHP or HEMP diets are likely to have contributed to increases in muscle antioxidant status. The energy and protein concentration of LFD had no effect on the health claimable n-3 fatty acid concentration in meat.

Interaction of diet and long ageing period on lipid oxidation and colour stability of lamb meat

Eighty-four crossbred wether and ewe lambs were allocated to four finishing diets. The diets were: Lucerne pasture (n=24), Annual ryegrass with sub clover pasture (n=18), Standard commercial feedlot pellets (n=24) and Annual ryegrass based pasture and commercial feedlot pellets (500g/day/head) (n=18). After 8weeks of feeding the lambs were slaughtered and the m. longissimus (LL) and m. semimembranosus (SM) were vacuum packaged and held chilled for 5 (fresh) or 60 (long aged) days, after which samples of each were displayed for 4days under simulated retail conditions. Irrespective of muscle type the long aged samples exhibited a rapid reduction in redness (a*-values) and R630/580nm ratio values such that consumer acceptable thresholds for both traits were quickly exceeded providing limited shelf life. Long ageing also lead to high TBARS levels measured as MDA mg/kg muscle suggestive of a product likely to exhibit rancidity and off flavours from lipid oxidation.

Rosiglitazone maleate increases weight gain and body fat content in growing lambs

Thiazolidinediones (TZD) are synthetic orally active peroxisome proliferator-activated receptor γ ligands used in the treatment of diabetes mellitus. The peroxisome proliferator-activated receptor γ gene plays an important role in regulating fat cell development, energy balance, and lipid metabolism in adipose and skeletal muscle tissue. There is interest in pharmacologic or nutritional means that may complement genetic techniques to improve growth and carcass composition of lambs and the major aim of the present study was to determine whether TZD impact on growth performance and meat quality of growing lambs. An initial study with four cross-bred lambs confirmed that rosiglitazone maleate is absorbed after oral dosing for 7 days. A second study was conducted with 30 cross-bred lambs to investigate the effects of sex (ewe vs wether) and dose of orally administered rosiglitazone maleate (0, 8 and 24 mg/day) for 55 days on growth performance, body composition, plasma metabolites and insulin and meat quality. Feed intake tended to increase linearly with dose of TZD (1521, 1816 and 1878 g/day for 0, 8 and 24 mg/day, P = 0.07) over the entire study, and particularly during the second half of the study (P < 0.05). There were both linear (P = 0.05) and quadratic (P = 0.04) responses in average daily gain to TZD (215, 270 and 261 g/day) with the quadratic response being most pronounced over the second half of the study (P = 0.004). As a result of the increased feed intake back fat (9.4, 11.1 and 13.5 mm, P < 0.001) and carcass fat (27.5%, 29.2% and 30.1%, P = 0.05) increased linearly with dose of TZD. However, there was no effect of TZD on internal fat depots. Plasma non-esterified acid concentrations increased linearly (0.37, 0.39 and 0.41 mM, P = 0.01) whereas plasma insulin concentrations (23.2, 26.9 and 20.9 mU/L, P = 0.05) and the homeostatic model assessment (6.82, 7.73 and 5.98, P = 0.05) exhibited quadratic responses to TZD. There were no significant effects of TZD on muscle pH, temperature or colour although muscle pH was higher at any temperature in ewes (+ 0.05 of a pH unit, P = 0.036) than in wethers. In conclusion, these data confirm that rosiglitazone maleate was rapidly absorbed from the digestive tract of growing ruminant lambs and was metabolically active. Oral TZD treatment appeared to mitigate against the inhibitory effect of carcass fatness on feed intake but the additional energy consumed was in turn deposited as fat.

Factors influencing the occurrence of high ultimate pH in three muscles of lamb carcasses in Australia

Chilled lamb meat exported from Australia has, on occasions, been rejected by importing countries due to greening, after only 6 weeks of storage time. Greening is known to be more prevalent in high ultimate pH (pHu) beef meat (>5.9). There are few data available for lamb carcasses in Australia on the occurrence of high pHu meat, which may have an impact on the understanding and control of quality and greening during storage. The aim of this project was to determine the prevalence of, and influencing factors for, high pHu meat in a range of muscle types in lamb carcasses in Australia. Muscle pHu data were collected from a total of 1614 carcasses from 78 lots at four lamb processing plants in Victoria and New South Wales in autumn and spring of 2013. The pHu of the knuckle (rectus femoris), rack (longissimus) and blade (infraspinatus) was measured and data on carcass and lot characteristics were recorded. Data were subjected to restricted maximum likelihood and generalised linear mixed model analysis. The mean pHu of the knuckle, rack and shoulder were 6.06, 5.79 and 6.12 respectively, and the main factors influencing muscle pHu and occurrence of dark-cutting were breed, season, electrical stimulation and carcass weight. Merino lambs had a higher pHu in the blade and knuckle than did other breeds (P < 0.05, P < 0.01 respectively). Lambs processed in autumn had a higher predicted pHu in the blade and knuckle and a higher percentage dark-cutting (DC; pHu >6.0) for those muscles, than did those processed in spring (P < 0.05). Carcasses that had been electrically stimulated had a higher %DC and a higher pHu in all three muscles (P < 0.05). Carcass weight had a significant effect on the pHu of all three muscles (P < 0.001), with heavier carcasses having a lower pHu and lower %DC. The pHu of the rack was not a reliable predictor for the pHu in other muscles of the lamb carcass. In conclusion, the high occurrence of DC in the muscles, particularly the blade and knuckle, suggests that these muscles may be at risk for producing greening in the vacuum bag during storage.

Genetic parameters for meat quality traits of Australian lamb meat

Genetic parameters were estimated for a range of meat quality traits recorded on Australian lamb meat. Data were collected from Merino and crossbred progeny of Merino, terminal and maternal meat breed sires of the Information Nucleus programme. Lambs born between 2007 and 2010 (n=8968) were slaughtered, these being the progeny of 372 sires and 5309 dams. Meat quality traits were found generally to be of moderate heritability (estimates between 0.15 and 0.30 for measures of meat tenderness, meat colour, polyunsaturated fat content, mineral content and muscle oxidative capacity), with notable exceptions of intramuscular fat (0.48), ultimate pH (0.08) and fresh meat colour a* (0.08) and b* (0.10) values. Genetic correlations between hot carcass weight and the meat quality traits were low. The genetic correlation between intramuscular fat and shear force was high (-0.62). Several measures of meat quality (fresh meat redness, retail meat redness, retail oxy/met value and iron content) appear to have potential for inclusion in meat sheep breeding objectives.

Factors affecting the colour of lamb meat from the longissimus muscle during display: the influence of muscle weight and muscle oxidative capacity

Spectrophotometric measures were used to determine the redness:browness (R630/R580) of 4238 lamb longissimus muscle after 3 days under simulated display. The results were analysed using linear mixed effects models. Environmental factors represented by effects such as kill group and site of production produced the greatest variation of up to 2.76 units in R630/R580. Isocitrate dehydrogenase activity, reflecting muscle oxidative capacity, reduced R630/R580 by 0.5 units. Selection for high muscling sires increased R630/R580 by 0.27 units, likely due to changes in muscle oxidative capacity. Lamb carcass weight also increased R630/R580 by 0.5 units. Analysis of genotypic factors influencing lamb size and growth rate such as sire type and dam breed further supported that increased growth rate improves meat R630/R580. Our findings suggest that breeding for increased growth rate and increased muscle weight could result in Australian lamb meat retaining its red colour for extended periods whilst on display.

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.

Genotype and age effects on sheep meat production. 3. Meat quality

A 5 × 4 factorial experiment was designed in which lambs representing five genotypes were slaughtered at four ages (110, 236, 412 and 662 days of age or 4, 8, 14 and 22 months of age). The genotypes represented were Poll Dorsetgrowth × Border Leicester Merino (PDg × BLM), Poll Dorsetgrowth × Merino (PDg × M), Poll Dorsetmuscling × Merino (PDm × M), Merino × Merino (M × M) and Border Leicester × Merino (BL × M). In total, 595 animals were slaughtered and carcass traits, composition and meat quality measured. As the animals grew older, intramuscular fat percentage (IMF) increased in the longissimus (LL) muscle and as the proportion of Border Leicester parentage increased so did the levels of IMF. There was a significant sire breed effect on LL pH at 24 hours after slaughter (pH24), with Merino-sired animals having a higher pH24 than both Poll Dorset and BL-sired animals. A significant dam breed effect was found for pH24 of the semitendinosus (ST) muscle, with lambs born to Merino ewes having a higher pH than those born to BLM ewes. A significant effect of sire estimated breeding value (EBV) for yearling muscling (YEMD) on LL pH was detected indicating an increase in pH as the sire EBV for muscling increased. There was a significant Merino effect for ultimate pH of the ST, with Merino-sired animals having a higher ultimate pH than both Poll Dorset and Border Leicester-sired animals. Sucker lambs had a significantly lower ST pH than older animals. As animal age at slaughter increased, the LL became darker based on L* values. There was a significant increase in a* values as animals became older, with 14 and 22-month-old animals having redder muscle. As LL pH and YEMD EBV increased, a* values decreased. There was a significant interaction between animal age and post mortem aging time such that sucker lambs (4 months old) produced LL with the lowest shear force after 5 days of aging and exhibited the greatest decline in shear force with aging. There was a significant increase in semimembranosus muscle shear force for PDm-sired animals (mean ± s.e., 66.5 ± 1.99 Newtons) compared with other genotypes at 61.4 ± 1.28 Newtons, but this could not be attributed to YEMD.

Genotype and age effects on sheep meat production. 2. Carcass quality traits

The present study examines carcass quality traits in different genotypes of Australian sheep slaughtered at 4, 8, 14 and 22 months of age. Poll Dorsetgrowth × Border Leicester Merino (PDg × BLM), Poll Dorsetgrowth × Merino (PDg × M), Poll Dorsetmuscling × Merino (PDm × M), Merino × Merino (M × M) and Border Leicester × Merino (BL × M) genotypes were compared. Sires were selected on the basis of growth (PDg, M and BL) and muscle (PDm) using estimated breeding values (EBVs). Approximately 150 mixed sex animals were slaughtered at each age (595 in total for the four slaughters) and carcass quality traits, including hot carcass weight, loin and semitendinosus (ST) muscle weights, GR fat, fat C, rump fat depth and eye muscle area (EMA), were determined at 45 min to 3 days postslaughter. With age, all carcass quality traits increased in magnitude. Merinos produced the lightest and leanest carcasses (P < 0.01) with lowest values in nearly all the carcass quality traits. At 4 and 8 months of age carcass and loin weights, EMA and GR fat measures were greater (P < 0.01) in second-cross PDg × BLM sheep than all other genotypes. However, traits related to muscle content were similar between first- and second-cross Poll Dorset genotypes at 14 and 22 months of age. The BL × M genotype had lower values than the PD × M genotypes for these traits, at all ages. Traits related to carcass fatness showed that sheep with Border Leicester genetics tend to deposit more fat (P < 0.001) in the carcass than those with Merino or Poll Dorset genetics from 14 months of age onwards. Most carcass quality traits did not differ (P > 0.05) between first-cross Poll Dorset genotypes selected for growth or muscling (PDg × M v. PDm × M). Sires with high muscling EBVs are associated more with shorter carcass length than low muscling EBVs. From ~8 months of age, wethers had greater values (P < 0.05) than ewes of the same age for most carcass quality traits related to size and muscle development, but no effect was present for carcass quality traits that were related to fat deposition. It was clear that the carcass weight of M × M at 8 and 14 months were similar to that observed in PDg × BLM at 4 and 8 months, respectively. Loin weights of M × M and BL × M at 13 and 8 months were similar to that weights observed in PDg × BLM at 8 and 4 months of age, respectively. Animals slaughtered to a muscle weight specification will reach the target at a younger age when they have more Poll Dorset than Border Leicester background genetics. Alternatively animals slaughtered at a specified fat score (using fat C or rump fat depth) will reach the specification at a younger age when they have more Border Leicester than Poll Dorset genetics.

Unravelling the complex interactions between genetics, animal age and nutrition as they impact on tissue deposition, muscle characteristics and quality of Australian sheep meat

The combined effects of age and genetics and Poll Dorset sire and growth path were studied in two separate experiments (n = 595 and 627, respectively). In the first experiment, containing genotype crosses typically used in Australia (Merino, Poll Dorset, Border Leicester) and sires selected for growth or muscling, sheep were slaughtered at 4, 8, 14 and 22 months. The second experiment used Poll Dorset sires selected for high muscling, fat or growth with progeny having two levels of nutrition postweaning. Border Leicesters expressed higher levels of carcass fat percentage and intramuscular fat and produced the heaviest carcass. Merinos had the lowest subcutaneous fat depth and highest carcass lean percentage when compared at the same age. The progeny of Poll Dorset sires selected for high muscling (PDm) expressed a shift toward glycolytic fibres relative to those from Merino sires, and PDm sires produced progeny with reduced spine and limb length and higher carcass muscle : mineral ratios, suggesting skeletal stunting. Genotype meat quality differences were minimal except that PDm sire topsides were tougher and Merinos produced higher pH meat. With age (4–22 months), lambs became heavier and fatter, fibres shifted towards oxidative and away from glycolytic, muscle myoglobin increased, the meat became darker and redder and tenderness declined. Early weaning had no effect on the time to reach slaughter weight, provided nutrition was not restricted. The sire genetics influence on the carcass composition far outweighed the effect of nutrition postweaning. Lambs on a restricted diet tended to have less acceptable meat quality but this was not evident in lambs from sires selected for high fatness. Sensory tenderness was improved and intramuscular fat was higher in lamb progeny from sires selected for high fatness.

Sheep genotype, age and muscle type affect the expression of metabolic enzyme markers

The objective of this study was to determine whether genotype, age (4, 8, 14 and 22 months), sex (ewe and wether) and muscle type influence ovine (n = 587) muscle metabolic characteristics. The genotypes represented were Poll Dorsetgrowth × Border Leicester Merino, Poll Dorsetgrowth × Merino, Poll Dorsetmuscling × Merino, Merino × Merino and Border Leicester × Merino. Between 4 and 22 months of age, myoglobin concentration within all muscles and all genotypes doubled, with the bulk of this response occurring between 4 and 8 months of age. Levels in the longissimus thoracis et lumborum (LT) and semimembranosus muscles were double those seen in the semitendinosus (ST) muscle, and Merinos had the lowest myoglobin concentrations of all genotypes. The other aerobic indicator, isocitrate dehydrogenase, had lower activity in the ST compared with the LT, was lower in 22-month-old sheep compared with all other ages, and decreased as selection for leanness increased. Both phosphofructokinase and lactate dehydrogenase activity tended to increase with age, were lower in the ST compared with the LT, and had higher activity in the Border Leicester × Merino sheep. The correlation between the percentage of total myofibre area comprising type 2X myofibres and metabolic markers was far higher for the oxidative indicators isocitrate dehydrogenase and myoglobin, which both decreased as relative area of type 2X fibres increased. However, the strongest correlations were with the relative area of type 2A myofibres, which were consistently high for both oxidative and glycolytic metabolic markers implying positive coregulation with both energy producing pathways.