Graham Gardner

Non-invasive and non-destructive measurements of fat depth are sought after within the beef industries, as overfat carcases cause significant economic loss and wastage for processors. Within the Australian beef industry fat depth is measured manually, however this has the disadvantage of being destructive, subjective and time-consuming [1]. Since biological tissues in animals, feature a high contrast in their dielectric properties (skin, fat, and muscle) at microwave frequencies [2], this represents an opportunity to different fat from lean and thus estimate fat depth and body composition of carcases and live animals. This concept has been tested in lamb carcases where a low-cost portable Microwave System has been developed for measuring C-site back fat depth [3]. This paper details the testing of a similar device in beef, where we hypothesised that it would accurately predict P8 and rib fat depth in beef carcases.

In the meat industries, overfat carcases cause significant economic loss due to the labour required for trimming fat, and the waste that it represents. Fat is the most variable component, both in its amount and distribution in the carcase, and on this basis the measurement of carcase fat depth is the cornerstone of most carcase classification schemes for beef, lamb and pork worldwide [1,2]. Fat depth is often measured manually, however this has the disadvantage of being destructive, subjective and time-consuming. The ability to estimate fat depth accurately via a non-invasive and non-destructive technique is therefore highly sought after [3]. One solution showing considerable promise for determining carcase fatness is a Microwave System (MiS) using low power non-ionizing electromagnetic waves [4]. Since biological tissues in animals, feature a high contrast in the dielectric properties (skin, fat, muscle and bone) at microwave frequencies [4], MiS can accurately evaluate the fat depth and body composition of carcases and live animals. As an illustration of tissue parameters, the range of contrast available in X-ray imagery within soft tissues is less than 2%; whereas within microwave electromagnetic fields the range in relative dielectric constant goes from a minimum of about 4 in fat to a maximum of about 70 in muscle [5]. Furthermore, the microwave devices required to produce and measure these fields are low cost and highly portable. Working within these constraints a low-cost portable Microwave System has been developed for measuring back fat depth in lamb carcases. This paper details early testing of this device, testing the hypothesis that it will provide a reliable estimate of back-fat depth in lamb carcases.

During the pre-slaughter period, sheep may experience acute stress and extended periods of feed deprivation. Studies in slaughter cattle have shown a moderate impact on plasma non-esterified fatty acid (NEFA) concentration in cattle but a larger acute stress immediately prior to slaughter, demonstrated by marked increases in plasma glucose and lactate. Sheep undergo similar pre-slaughter management to cattle in Australia, thus we hypothesise that lambs will have a similar metabolic profile at slaughter. Blood was collected at exsanguination from 1,536 lambs (mean age at slaughter 298±57 days) from the Sheep Co-Operative Research Council Information Nucleus Flock. The lambs were managed on two research stations (Katanning, Western Australia and Armidale, New South Wales) and were assigned to ten slaughter groups based on carcass weight targets for the desired market. Lambs were yarded the day prior to slaughter, held in curfew on-farm for 2 hours, weighed and then transported to commercial abattoirs where they were held in lairage for an average of 17 .9±1. 79 hours. Blood was collected at exsanguination and the plasma was analysed for non-esterified fatty acids, glucose and lactate. Plasma metabolite concentrations differed markedly between slaughter groups (P<0.05). Across all of these groups the mean plasma NEFA, glucose and lactate concentrations were 1.57±0.45 mmol/1, 4.05±0.56 mmol/1 and 2.94±1.74 mmol/1. Contrary to our hypothesis, NEFA concentrations were markedly higher at slaughter in lambs compared with cattle. Alternatively lactate and glucose concentrations were lower than concentrations in slaughter cattle. This suggests that different mechanisms may exist between sheep and cattle in terms of their metabolic response to feed deprivation and acute stress during the pre-slaughter period.

Meat colour was measured in 7732 lambs produced at 8 sites across Australia over a 5 year period (2007-2011) and slaughtered in 125 groups as pari of the Sheep Cooperative Research Centre's information nucleus flock experiment. Lambs were the progeny of sites of different types (merino, maternal and terminal) selected for a diverse range in Australian Sheep Breeding Values for post weaning eye muscle depth (PEMD). 24 hours post slaughter them. longissimus was cut at the 12th rib, a probe was used to measure pH and the meat surface was allowed to bloom/oxygenate for 30 minutes before fresh colour measures of lightness (L*), redness (a*) and yellowness (b*) were captured using a Minolta colorimeter. These measures were analysed in a multivariate analysis before least square means were produced for L *,a* and b* using a linear mixed effects model in SAS. The base model included fixed effects for site, year of birth, slaughter group, sex and dam breed within sire type as well as random effects for sire and dam by year. In a second analysis sire PEMD estimates were included in the model as a covariate. Increasing sire PEMD across a range of -2 to 4 was associated with an increase (P<0.01) in the predicted means for L*, a* and b* by 1.15, 0.38 and 0.55 units respectively. When pH measured 24 hours post-m01iem was accounted for in the model, the impact of sire PEMD estimates on L *, a* and b* were halved. This suggests that selection for sires based on PEMD may impact meat colour via changes in muscle metabolism that affect the extent of glycolysis and pH decline post slaughter. Our findings suggest that using sires with high PEMD will improve the lightness and redness of the meat produced.

Supplying beef with consistent eating quality to consumers is vital to the beef industry. We investigated the relationship between eating quality and biochemical measurements, intramuscular fat (IMF), moisture content and heme iron. Six cuts (striploin, outside, rump, tenderloin, oyster blade and the topside) from 18 French cattle were grilled, medium or rare. In total 540 untrained French consumers rated the steaks for tenderness, flavour, juiciness and overall liking, according to MSA protocols. These scores were combined on a weighted basis (0.3, 0.3, 0.1, 0.3 respectively) to make a score called MQ4. The sensory scores were analysed using a mixed linear model with cut, age and country included as fixed effects, and animal ID as a random term. The biochemical measurements were then incorporated one at a time as covariates into the model, as well as their interactions with all fixed effects to assess their association with the sensory scores. IMF (range 0.23-9% wet matter) had a positive, linear, relationship with flavour and overall liking (magnitude of effect 6.08 and 5.94 across the IMF range). Moisture content (range 70-77% wet matter) had a negative, linear, relationship with flavour and overall liking (magnitude of effect 6.35 and 6.15 across the moisture content range). When together in the same model, both remained significant implying that moisture content has a relationship with eating quality beyond its con·elation with IMF. All other relationships were not significant. The effect of IMF is smaller than that seen by Pannier et al. in Iamb striploin (10.1, 9.1), but slightly larger than lamb topside (6.6, 5.4).

Scott Technology Ltd. have developed a robotic boning system for use in lamb abattoirs. This system operates at chain speed and makes use of2D x-ray images taken of the carcass to identify cutting lines. The opportunity exists to replace this x-ray system with a dual energy x-ray absorptiometry (DEXA) system which meets robotic image requirements while also enabling the determination of body composition. This study tested a prototype DEXA design that we have developed with the hypothesis that this system could determine body composition at chain speed. 12 Merino lamb carcasses with weights ranging between 14 and 16.3 kg were scanned using the prototype D EXA system to derive an estimate of fat composition. The carcasses were then scanned using Computed Tomography (CT) to determine fat, lean and bone weights which were then expressed as a percentage of carcase weight. Composition of these carcases varied between 9-15.5% for CT fat, 68-72.5% for CT lean, and 16.2 to 20.7% for CT bone. The DEXA estimate of fat composition was then used to predict CT fat, lean, and bone percentage. Our findings supported the hypothesis as the DEXA system was able to predict carcase composition with a precision (R2) of 0.88, 0.34, and 0.60 for predicting the percentage of CT fat, CT lean and CT bone in the carcase. These results demonstrate the capacity of this prototype DEXA system to estimate body composition and lean meat yield in lamb carcasses at abattoir chain speed.

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.