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Although there has been a decline in sheep numbers in Australia and New Zealand, both countries remain significant producers and exporters of sheep meat. The ongoing demand for more sustainable and ethical animal farming systems and practices requires sheep production industries to be both vigilant and responsive to consumer and the broader societal needs. Demonstration of continuous improvement in animal welfare is paramount and the welfare risks and challenges confronting Australasian sheep industries now and into the future are discussed. [ABSTRACT FROM AUTHOR]

Data from samples of longissmus lumborum (LL) and semimembranosus (SM) muscles from 391 lamb carcasses, which had been packaged in overwrap (OW) or high oxygen modified atmosphere packaging (MAP O2 ) systems and then subjected to simulated retail display, were used to estimate genetic variation for colour stability traits of lamb meat as a step in identifying a trait for genetic evaluation. Traits included the ratio of the reflectance of light at wavelengths of 630 nm and 580 nm (oxy/met) measured at a single time point at the end of the display period (day 3 under OW; day 8 under MAP O2 ) and the predicted time for oxy/met to reach a benchmark value. Under OW and MAP O2 , the measures of meat colour stability of the LL tended to be of moderate heritability (0.09-0.29), but for the SM were of low heritability (0-0.10). Improving retail colour stability of lamb loins through selection of genetically superior animals may be better based on measurement of oxy/met., (Crown Copyright © 2019. Published by Elsevier Ltd. All rights reserved.)

The colour of bloomed m. longissimus was measured 24h post slaughter for 8165 lamb carcasses produced over 5years across 8 sites in Australia. Intramuscular fat across a 2 to 8% range and shortloin fat weight were positively associated with meat lightness (L*), redness (a*), yellowness (b*), hue and chroma (P<0.01). Shortloin muscle weight was negatively associated with these meat colour parameters (P<0.01), although this was largely accounted for by correlated changes in intramuscular fat (P<0.01). The effect of sire breeding values for lamb weight, shortloin muscle depth and fat depth on loin L*, a*, b*, hue and chroma were small and varied between lambs of different sire type, dam breed and sex. Thus selection for lean meat yield will have neutral or positive effects on meat colour, while selection for increased intramuscular fat will make the bloomed colour of lamb meat lighter and redder., (Copyright © 2017. Published by Elsevier Ltd.)

The longissmus lumborum (LL) and semimembranosus (SM) muscles from 391 lamb carcasses, derived from various breed types, were used to investigate the effect of animal/muscle factors, packaging type [over-wrap (OW) or high oxygen modified atmosphere packaging (MAP O2 )] and duration of display on redness of meat during simulated retail display. Using statistical models the time required (in days) for redness to reach a threshold value of 3.5 (below this is unacceptable) was predicted. High levels of iron in the SM, but not LL, reduced the time for redness to reach 3.5 by 2-2.6days in MAP O2 and 0.5-0.8days in OW. The greater the proportion of Merino breed type, the shorter was the time for redness to reach the value of 3.5, an effect consistent across muscles and packaging types. In summary, breed type, packaging format, muscle and muscle iron levels had a significant impact on colour stability of sheep meat in oxygen-available packaging systems., (Copyright © 2017. Published by Elsevier Ltd.)

M. longissimus colour was measured from 8165 lambs at 24h post-mortem using a chromameter. The impact of production factors (site and year of production, slaughter group, sex, age and breed type) and muscle traits (hot carcass weight, pH24, isocitrate dehydrogenase (ICDH) activity, myoglobin, iron and zinc concentrations) on meat lightness (L*), redness (a*), yellowness (b*), hue and chroma were analysed. Greater differences in meat colour were seen between different slaughter groups and sites of production than across the range of any muscle traits. Of the muscle traits analysed, changes in pH24 had the greatest effect on meat a* (2.5 units), while myoglobin had the greatest effect on meat L* (2.9 units). The 3.1 L* unit darkening of meat with increasing lamb age (from 140 to 400days) was accounted for by increased myoglobin concentration. These results suggest that production factors are having substantial effects on lamb colour independent of known influencing muscle traits such as myoglobin concentration and pH., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The relationship between vitamin E supplementation rate and colour stability was investigated using 70 mixed sex 6-8 month old crossbred lambs. An initial group of 10 were slaughtered, while the remainder were fed a pellet ration containing either 30, 150, 275 or 400 IU vitamin E/kg ration or on green pasture for 56 days. After slaughter, carcases were halved; one side packed fresh (5 days) and the other in CO2 (21 days), both at 2°C. Five muscles were set for retail display for 96 h. The oxy/metmyoglobin ratio was measured every 12 h. Colour stability increased with increasing muscle vitamin E until an apparent maximum effect for vitamin E concentration (3.5-4.0mg α-tocopherol/kg tissue) was reached beyond which no further response was evident. This was reached within 3-4 weeks (275 IU treatment), and meat from these lambs should reach 60 h retail display with a satisfactory surface colour. This effect was most apparent in aerobic muscle types and meat aged post slaughter., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Pre-slaughter live weight, dressing percentage, and hot standard carcase weight (HCWT) from the 2007, 2008, 2009 and 2010 birth-years of the Information Nucleus Flock Lambs (n=7325) were analysed using linear mixed effects models. Increasing the sire breeding value for post-weaning weight (PWWT), and c-site eye muscle depth (PEMD), and reducing the sire breeding value for fat depth (PFAT) all had positive impacts on HCWT. The magnitude of the PWWT effect was greater in pure bred Merinos compared to Maternal and Terminal sired progeny. The improved HCWT resulting from increased PEMD was entirely due to its impact on improving dressing percentage, given that it had no impact on pre-slaughter live weight. There were marked differences between sire types and dam breeds, with pure-bred Merinos having lower pre-slaughter weight, reduced dressing percentage, and lower HCWT than progeny from Terminal and Maternal sired lambs or progeny from Maternal (1st cross) dams., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

This paper introduces a series of papers in the form of a special edition that reports phenotypic analyses done in parallel with genotypic analyses for the Australian Sheep Industry Cooperative Research Centre (Sheep CRC) using data generated from the information nucleus flock (INF). This has allowed new knowledge to be gained of the genetic, environment and management factors that impact on the carcase and eating quality, visual appeal, odour and health attributes of Australian lamb meat. The research described involved close collaboration with commercial partners across the supply chain in the sire breeding as well as the meat processing industries. This approach has enabled timely delivery and adoption of research results to industry in an unprecedented way and provides a good model for future research., (© 2013.)

This paper integrates the key industry findings from the twelve preceding papers in this special edition of Meat science. In so doing, various animal factors important for the quality of Australian lamb meat are highlighted for sensory, visual appeal and human health attributes. Intramuscular fat concentration (IMF) was found to be a key element of eating quality that interacts both positively and negatively with a range of other factors. Shear force, IMF, colour stability and docosahexaenoic acid (DHA) will likely respond to genetic selection whilst other omega-3 fatty acids require nutritional intervention. Australian lamb meat can generally be regarded as a good source of the minerals iron and zinc; and a source of omega 3 fatty acids when finished on green pasture. Breeding priorities for meat quality will likely depend on breed type with improvement of meat colour stability more important for the wool focused Merino breed and improvement of sensory quality for the terminal sire breeds., (Copyright © 2013. Published by Elsevier Ltd.)

The impact of selecting for lean meat yield using breeding values for increased eye muscle depth (PEMD) and decreased fat depth (PFAT) on the consumer acceptance of lamb meat was evaluated. Consumer sensory scores (tenderness, juiciness, flavour, odour, overall liking) were obtained for the longissimus lumborum (loin) and semimembranosus (topside) muscles of 1471 lambs. On average loin samples were more acceptable for consumers. Sensory scores increased with higher IMF levels, with lower shear force levels, and when animals were younger and less muscular. Increasing PEMD decreased tenderness, overall liking and flavour scores in both muscles, and decreasing PFAT reduced tenderness within the loin samples only. This negative impact of PEMD and PFAT is not solely driven through the phenotypic impact of IMF and shear force on sensory scores. Our results confirm the growing concerns that selecting for lean meat yield would reduce consumer eating quality, and highlight that careful monitoring of selection programmes is needed to maintain lamb eating quality., (© 2013.)

Selection for lean growth through Australian Sheep Breeding Values (ASBVs) for post weaning weight (PWWT), eye muscle depth (PEMD) and c-site fat depth (PFAT) raises concerns regarding declining intramuscular fat (IMF) levels. Reducing PFAT decreased IMF by 0.84% for Terminal sired lambs. PEMD decreased IMF by 0.18% across all sire types. Female lambs had higher IMF levels and this was unexplained by total carcass fatness. The negative phenotypic association between measures of muscling (shortloin muscle weight, eye muscle area) and IMF, and positive association between fatness and IMF, was consistent with other literature. Hot carcass weight increased IMF by 2.08% between 12 and 40 kg, reflective of development of IMF as lambs approach maturity. Selection objectives with low PFAT sires will reduce IMF, however the lower impact of PEMD and absence of a PWWT effect, will enable continued selection for lean growth without influencing IMF. Alternatively, the negative impact of PFAT could be off-set by inclusion of an IMF ASBV., (Copyright © 2013 The Authors. Published by Elsevier Ltd.. All rights reserved.)

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., (© 2013.)

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., (© 2013.)

There is a concern regarding the possible decline of nutritional value of meat with an increasing selection for lean meat yield. The selection for reduced fatness reduces muscle aerobicity and possible subsequent mineral concentrations. Average concentrations of iron and zinc of 5625 lamb longissimus muscles were 2.03 and 2.43 mg/100 g, qualifying as a good source claim for the majority of the population. Reduced post-weaning fat depth was associated with decreased concentrations of iron but not zinc, whereas post-weaning eye muscle depth and weaning weight were not associated with either mineral. These results confirm that the impact of lean meat yield selection on these minerals is minimal, but should be monitored to avoid lower levels. Both minerals had a positive relationship with age at slaughter, highlighting age as a key determinant of the concentration of these nutrients. The magnitude of the positive associations of isocitrate dehydrogenase and myoglobin with iron was larger than for zinc, but they strongly indicated the association of these aerobic makers with both minerals., (© 2013.)

An experiment was conducted to compare the effect of two chilling rates (Con and Fast) on colour change of lamb meat during simulated retail display. Measurements were made on 3 muscles; LD (m. longisimuss dorsi), SM (m semimembranosus) and ST (m. semitendinous). Meat samples from 32 Merino crossbred lambs were vacuum packed and stored for 5 days at 2 °C, then cut and overwrapped in polyvinyl chloride film on black polystyrene trays, stored in a display cabinet at 4 °C with lights on and measured twice daily for 4 days, using a Hunterlab minilab 45/20L D65, aperture 10°. Sarcomere length was shorter, shear force higher and colour change greater in meat from the Fast treatment compared to the Con treatment. Colour differences between treatments were likely due to oxygenation (bloom) as well as oxidation effects. Chill rate is important when characterising colour change during display and should be considered in measurement protocols., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

This study investigated the effect of computerised tomography imaging (CT scan), for carcase composition determination, on the oxy/metmyoglobin ratio, hue and L(∗), a(∗) and b(∗) scores of M. longissimus dorsi from both beef and lamb. Beef and lamb M. longissimus dorsi were divided into four proportions and randomly allocated to one of the following treatments; CT 30 day aged; CT fresh; control 30 day aged; control fresh. Colour measurements were made over a 96h retail display period. CT scan had little effect on the colour of both lamb and beef across all colour parameters. There was a small negative affect observed in CT aged samples (P<0.05) for ratio, hue, a(∗) and b(∗) values, however these differences were so small that they are unlikely to impact upon the commercial shelf-life of the product. Other factors such as aging, species and vitamin E concentration play a much greater role in colour stability than CT. Aged M. longissimus dorsi clearly had a worse colour stability than the fresh packaged samples, while beef was a lot more colour stable than lamb. It appears that CT scan for the purpose of body composition determination will not have any commercially relevant impact on colour stability of both beef and lamb.

The use of alternating frequencies during stimulation can increase stimulation response of a medium voltage electrical stimulation unit (MVS) by increasing the rate of pH decline. Various combinations of frequency modulation were tested in experiment 1 to determine the treatment resulting in the greatest stimulation response; the lowest initial pH, fastest rate of pH decline, highest temperature at pH 6 and the highest number of carcasses with a pH of 6 by 25(o)C and the treatment achieving the highest number of carcasses in the pH temp window (temperature at pH 6 between 18-25(o)C). The objective meat quality of these treatments compared to an unstimulated treatment was tested in experiment 2. Modulating the frequency (Hz) across the 6 segmented electrodes of the MVS by 10, 15, 25, 10, 15, 25Hz (Treatment 6, using a pulse width: 2.5ms, current: 1A) resulted in the greatest stimulation response. This treatment may be suitable for abattoirs that hot bone sheepmeat and require fast pH declines to ensure minimal cold shortening of meat. However, this treatment did not result in the tenderer meat despite the higher stimulation response. This treatment may have induced a greater number of contractions overall and therefore a greater pH decline response but resulted in less myofibrillar disruption compared to the other treatments due to a concomitant decreased force of contraction thus reducing potential tenderisation. Maintaining a constant frequency of 15Hz (Treatment 1; pulse width: 2.5ms, current: 1A) resulted in a higher number of carcasses in the pH temp window required (temperature at pH 6 between 18-25(o)C) in part A (P<0.05) and in addition to the higher tenderness levels this treatment may be more appropriate to satisfy the overall demands of abattoirs using these systems. This paper has also demonstrated electrical stimulation results in tenderer meat compared to unstimulated meat even after 30d of ageing (2.53±0.4 compared to 2.85±0.1 for the loin (M. longissimus thoracis et lumborum) (P<0.01) possibly due to a protective benefit of stimulation on meat tenderness. Overall, no detrimental effects of modulating frequency were observed on drip loss or retail colour display despite a greater rate of colour change observed with the modulated frequency treatment and the longer aged product.