David Pethick

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).

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.