Liselotte Pannier

In addition to nutritional attributes and lean meat, eating quality is a key driver influencing the consumer demand for sheep meat. It is generally believed that meat from older animals reduces the overall consumer acceptance of meat products, however there are limited sensory studies available to define these differences within untrained consumers, or to identify factors that affect them. A lamb versus hogget comparison study was conducted, which was part of a larger sens01y experiment within the Information Nucleus program of the CRC for Sheep Industry Innovation. This study tested genetic and non-genetic factors, and objective meat quality traits on sensory scores. We hypothesised that hogget meat will have lower sensory scores compared to lamb meat. Sensory scores were generated on the longissimus thoracis et lumborum (loin) and semimembranosus (topside) muscle from 189 Merino lambs, average age 355 days, and 209 Merino hoggets, average age 685 days. Five day aged grilled steaks were tasted and scored (1-100 score) by untrained consumers for tenderness, juiciness, flavour and overall liking. The difference in magnitude of sensory scores of the topside was greater than for the loin. Lamb topside had 8.4, 7.0, 3.3 and 5.8 more sensory scores for tenderness, overall liking, juiciness and flavour than hogget topside samples, whereas the lamb loin had only 4.7, 2.7, 1.6 and 2.2 more sensory scores for tenderness, overall liking, juiciness and flavour than hogget loin samples (P<0.01). Within each age group loins were more acceptable than topsides. In support of our hypothesis, older sheep had reduced sensory scores however these differences were minimal for the loin. These preliminary results highlight the better eating quality of lambs but show an acceptable eating quality of hogget meat, particularly for the loin, which opens the possibility of developing a high quality hogget product.

Sensory enjoyment is one of the key drivers that influences the consumer demand for lamb in Australia. One of the key factors that determines consumer satisfaction of lamb is intramuscular fat (IMF). Yet the challenge is to balance this against the industry aim of selecting for lean meat yield using Australian Sheep Breeding values for post-weaning eye muscle depth (PEMD) and subcutaneous fat depth at the c-site (PFAT), as these have been shown to decrease IMF levels. Hence, we hypothesised that selection for reduced PFAT and increased PEMD will reduce the sensory scores of lamb and that this relationship is driven through reduced LMF levels. Sensory scores were generated on both the longissimus thoracis et lumborum (loin) and semimembranosus (topside) muscle from 1,434 lambs. Five day aged grilled steaks were tasted by untrained consumers who scored (1-100 score) the samples for tenderness, juiciness, flavour, odour and overall liking. Increasing PEMD was associated with 5.3, 3.6 and 3.1 lower sensory scores for tenderness, overall liking and flavour for both the loin and topside samples. Decreasing PFAT was associated with a 3.1 score reduction for tenderness within the loin samples only All sensory scores increased with higher IMF levels, most strongly for juiciness and flavour, however in this analysis variation in IME levels did not appear to explain the impact of either PEMD or PFAT. This illustrates that the associations seen between PEMD and PFAT with the sensory scores are not solely driven through the phenotypic impact of IMF, in contrast to our initial hypothesis. Yet in support of our hypothesis, selection for more muscular and leaner animals did reduce the sensory score, confirming our growing concerns that selecting for lean meat yield would reduce consumer eating quality. This highlights the need for careful monitoring of selection programs to maintain the eating quality of lamb.

Increasing lean meat yield % (LMY%) and rapid growth are important profit drivers in the sheep supply chain. To optimise these traits, Australian prime lamb producers use the Carcase Plus Index (CP) for selecting sires. The index originally combined breeding values for weight, eye muscle depth and decreased fat depth, with weightings of 60:20:20 (old CP). Due to perceived gains in leanness in Terminal sires, and concern over reducing intramuscular fat levels in lamb meat, this index was altered to the current weightings of 65:30:5 (new (CP). Given that selection for reduced fat depth results in an increase in LMY%, we hypothesised that the new CP will return less LMY% and therefore reduced carcase value compared to the old CP Lamb carcases (n=1,800) from the Sheep CRC Information Nucleus Flock were collected from 6 research stations over 5 years. Carcases were scanned in 3 sections, fore, saddle and hind, using Computed Tomography (CT) to determine fat, lean and bone weights. Data was analysed using the allometric equation y=axb, fitted in its log-linearised form log y = log a + b.log x. The impact on carcase value was determined for new and old CP indexes in a 23 kg carcase. Within the 76 unit range of Terminal sire CP index values, the old CP Index delivered 2.2, 1.2 and 0.5 percentage units more lean in the fore, saddle and hind sections (P<0.01) compared to the new CP index. Across this same range in CP index values the old CP increased the value of carcase lean by $9.27, compared to $6.49 for the new CR equating to a value difference of $2.78 within a 23 kg carcase. Aligning with our hypothesis there was decreased gain in LMY% and carcase value using the new CP weightings. The cost in LMY% represents a substantial loss in daily profit for processors, especially when the potential improvement to intramuscular fat levels is not currently rewarded.

Increased growth rate and carcass lean meat yield % are key profit drivers for the lamb industry, however redistributing lean tissue to more highly priced parts of the carcase will also increase its value. Faster growing lambs are known to be leaner and less mature at slaughter. Therefore we hypothesised that selection for growth using the Australian Sheep Breeding Value (ASBV) for greater post weaning weight (PWWT) would increase whole carcase lean weight, when animals are compared at the same carcase weight. Lamb carcases (n=1,218) from the Sheep CRC Information Nucleus were scanned in sections (fore, saddle, and hind) using Computed Tomography (CT) to determine fat lean and bone weights. Data was analysed using the log-linearised allometric equation logy = log a + b.logx. Fixed effects were site-year, sex sire type, birth-type rear-type and kill group within site-year, with random terms sire and dam by year. For the same carcass weight PWWT caused no composition differences, except in female lambs which had 3.3% more carcase lean (P<0.01) across the 25 unis PWWT range. Alternatively for the same fat, lean or bone weight these tissues were all proportionately heavier in the saddle region of the high PWWT lambs by 3%, 7%, and 16% across the PWWT range. Aligning with our hypothesis, PWWT was associated with increased total carcase lean, although only in females. Unexpectedly, PWWT caused a redistribution of carcass tissues to the saddle region, particularly for bone and lean, implying an altered conformation in these high growth lambs. Conflicting with the premise of our hypothesis, these effects appear to be independent of maturity as there was no whole body increase in bone weight. Furthermore loin muscle myoglobin concentration in the high PWWT lambs was increased (by 0.03±0.018 mg/g tissue) rather than decreased as would be expected in a less mature animal, In conclusion, PWWT redistributes carcase weight to the saddle region of lambs.

Increasing lean meat yield % and redistribution of lean tissue to more highly priced parts of the carcase will increase its value. Selection for the Australian Sheep Breeding Value (ASBV) for greater post weaning eye muscle depth (PEMD) increased eye muscle area and weight of the eye of the short loin, although had minimal impact on carcase lean meat yield %. We hypothesised that selection using the PEMD-ASBV would increase saddle lean weight, without altering whole carcase lean weight when animals were compared at the same carcase weight Lamb carcases (ie1218) from the Sheep CRC Information Nucleus were scanned in ‘quarters’ (fore, saddle, and hind) using Computed Tomography (CT) to determine fat lean and bone weights. Data was analysed using the allometric equation y=axb, fitted in its log-Iinearised form logy = log a +b.logx. Fixed effects were site-yeast sex, sire type, bulb-type rear-type and kill group within site-year, with random terms sire and dam by year. At a given carcase weight the lean tissue was 4.2% heavier (P<0.01), and fat 8.7% lighter in the whole carcase (P<0.05) across the 7 unit PEMD range. When compared at the same lean weight, the lean tissue in the saddle was 4.9% heavier (P<0.01), and lean in the forequarter was 4.8% lighter (P<0.01) across the PEMD range. Aligning with our hypothesis, there was more lean tissue in the saddle, although unexpectedly this was at the expense of the forequarter only. The mechanistic reason for this redistribution is not clear, and will be investigated with more extensive sampling from tissues across the carcase. In contrast to our hypothesis, PEMD was associated with increased total carcase lean, and reduced fat. The leaner and more muscular composition appears to be independent of maturity as there was not a corresponding increase in bone weight. These impacts on lean weight and distribution to the loin will increase carcass value.

The Australian lamb industry uses Australian Sheep Breeding Values to select for reduced subcutaneous fat depth (PFAT) and increased lean meat yield. Selection for reduced PFAT increases oin muscle weight, with muscularity associated with reduced muscle aerobicity. As isocitrate dehydrogenase activity (ICDH) is a good indicator of oxidative metabolism, we hypothesised that selection for reduced PFAT would decrease ICDH. ICDH was measured within the loin muscle of 13971ambs and data was analysed using a linear mixed effects model (SAS) with fixed effects for site, kill group within site, sex, birth type-rear type, age of dam, sire type and dam breed within sire type, and random terms for sire and dam. Within this model, covariates such as PFAT, intramuscular fat percentage (IMF) and weight of short loin fat and muscle were included individually to assess their phenotypic association with ICDH. Aligning with our hypothesis, selection for reduced PFAT decreased ICDH by 0.52 µmol/min/g tissue over the 4 unit PFAT range. However, neither short loin muscle nor fat weight demonstrated strong associations with ICDH. This contrasts with the premise of our initial hypothesis that selection for negative PFAT would decrease ICDH via its impact on whole body muscularity and the associated effect on muscle aerobicity. Alternatively, ICDH was strongly associated with IMF, with a 4% decrease in IMF aligning with a 0.84 µmol/min/g tissue reduction in ICDH. Selection for negative PFAT strongly reduces IMF, and when both covariates were used concurrently within the ICDH model, PFAT was not significant. This may imply that the impact of PFAT on ICDH is delivered via its negative impact on IMF, and appears to be independent of whole body adiposity or muscularity.

The Meat Standards Australia (MSA) grading scheme for underpinning the eating quality of lamb is currently a pathways system with guidelines for best practice feeding, handling, slaughter, product aging and retail presentation of lamb cuts. This paper describes an experiment to determine the role of genetics to determine the continuous improvement in eating quality of lamb cuts. Eating quality data was generated from 745 lambs produced from 97 sires at 2 sites within the Information Nucleus (IN) program of the CRC for Sheep Industry Innovation. Grilled steaks were prepared from 2 cuts (m. longissimus lumborum — LD; m. semimembranosis — SM) with consumers scoring steaks for tenderness (TE), juiciness, liking of flavour and overall liking (OL) on a 0-100 scale. Consumers also assigned a quality rating to each sample: unsatisfactory satisfactory everyday, quality better than everyday quality or premium quality. The data for TE and OL were analysed using linear mixed models in ASReml with fixed effects of IN site, kill group, sex sire breed type and dam breed type. Sire and consumer session were random terms. There were significant effects (P<0.05) of cut (LI) >> SM), IN site, kill group and sire breed. Sire accounted for 5.3% and 3.3% of the total variance in TE and OL of both cuts with a sire range of 8-12 consumer points, sufficient to change the final consumer rating of the steaks. This preliminary study shows that genotype effects need to be considered in the development of a new MSA lamb grading model.