Liselotte Pannier

The USA and China are Australia’ s strongest sheep meat export markets , however insights into consumer perceptions of Australian sheep meat are limited . IMF and shear force are good indicators of eating quality for Australian consumers however the relationship for American and Chinese consumers is unknown. Eating quality scores (tenderness, juiciness, liking of flavour, and overall liking) were obtained from American, Australian, and Chinese consumers for Longissimus lumborum and semimembranosus muscles collected from Australian sheep (n=328). Shear force was negatively associated with all sensory traits, consistent for all countries. Whereas, increasing IMF levels had a positive impact on all eating quality scores for all countries, however the most significant change was observed for Australian consumers indicating their higher sensitivity towards IMF differences.

This study tested the palatability of lamb meat derived from pasture versus grain finishing systems. The loin and topside muscles from 105 lambs were collected. Sensory scores were generated using untrained consumers who tasted 5 day aged grilled steaks, scoring tenderness, juiciness, flavour and overall liking. Consumer scores did not differ in female lambs fed grain or pasture diets. However in wether lambs palatability scores for overall liking, tenderness and juiciness were higher for those on grain compared to those on pasture. Correcting for intramuscular fat accounted for most of these differences. These results confirm that Australian consumers do prefer grain-fed lamb meat, but only in wether lambs.

Genetic parameters were estimated for 5 sensory (overall liking, tenderness, juiciness, flavour and liking of odour) and 2 objective eating quality (EQ) traits (intramuscular fat, IMF, and shear force, SF), measured on loin and topside meat cuts (except IMF) produced by progeny from the Information Nucleus of the CRC for Sheep Industry Innovation. Heritabilities for sensory traits were low to moderate for loin and moderate to high for topside cuts. Loin IMF was highly heritable while SF was moderately heritable in both cuts. Genetic correlations among the sensory EQ traits were all positive and high (0.72-1.00). Genetic correlations between loin IMF and sensory traits were moderately positive and lowly positive for loin and topside respectively. SF had stronger, negative correlations with sensory EQ traits in the topside than in the loin. Overall liking may be improved more so through selection on IMF in the loin and SF in the topside.

The Australian lamb industry uses Australian Sheep Breeding Values for reduced postweaning subcutaneous fat depth (PFAT) to select for leanness and increased lean meat yield. Selection for reduced PFAT results in increased loin muscle weight (Gardner et al 2010) potentially leading to lower oxidative capacity in muscle (Greenwood et al 2006). Isocitrate dehydrogenase activity (ICDH) is an accepted indicator of aerobic metabolism, and therefore we hypothesise that selection for reduced PFAT results in a decrease in ICDH levels.

Introduction - Due to the nutritional importance of iron and zinc in human diets, marketing campaigns for lamb and beef are often focused on these minerals. Iron and zinc are associated with muscle aerobicity which may be diminishing in lamb meat due to selection practices targeting leanness and muscularity to increase lean meat yield (Pannier et al. 2010). Aerobicity of muscle has also been linked to intramuscular fat (IMF) percentage, and like-wise IMF is also depressed through selection for leanness (Gardner et a!. 20 I 0). Poor nutrition will also reduce carcase fatness and JMF, potentially limiting the scope for other genetic factors to impact. Therefore it seems plausible that the impact of selection for leanness will be less in a poor nutrition environment. Thus we hypothesised that selection for leanness would reduce carcase fatness and IMF, reduce aerobicity, and therefore reduce iron and zinc concentration, but these impacts will be depressed within flocks maintained on sites with poorer nutrition.

The Australian lamb industry selects for lean meat yield through the use of Australian Sheep Breeding Values, however there is concern regarding the impact of this on eating quality, as selection for lean growth has been linked with declining intramuscular fat (IMF) levels. Sires with reduced subcutaneous fat depth breeding values (PFAT) have reduced carcass fatness and increased loin muscle weight, whereas those with higher post-weaning eye muscle depth breeding values (PEMD) have increased muscularity. We hypothesised that selection for reduced PFAT and increased PEMD will decrease IMF levels. IMF was measured on 5556 lamb loins and linear mixed effects models were used to analyse this data. Fixed effects included site, drop, sex, birth type-rear type, dam breed and sire breed within sire type, sire type and kill group within site by drop, with sire and dam by drop identification as random terms. Hot carcass weight (HCWT), PFAT and PEMD were used as covariates to assess their association with IMF. HCWT (P<0.05) increased IMF levels by 2.40 IMF% units across the 28kg HCWT range. Reducing PFAT below 1.25 mm PFAT, decreased IMF by 0.61 IMF% units over the PFAT range. PEMD demonstrated a weaker association with IMF, reducing IMF levels by 0.44 IMF% units. Current selection objectives with high PEMD sires to increase lean meat yield would not impact as strongly on IMF levels as sires with low PFAT, however continuous selection for leanness might need to slow down to avoid IMF levels to drop below the consumer acceptable levels.

The objective of this study was to estimate the levels of iron and zinc in lambs from Merino and crossbred ewes from different genotypes and production systems in Australia (Western Australia, New South Wales, South Australia and Victoria) and to determine the genetic and non-genetic factors that affect iron and zinc concentrations. It was shown that site, sex and kill group within site significantly affected iron content. Lambs in Cowra and those in Kirby (both in New South Wales) had the lowest and highest levels, respectively. Females had 4% higher iron concentration than males and those slaughtered at a later age had higher iron levels. For zinc, site, sire and kill group within site had significant effects. At sites except for Cowra had higher zinc levels. Maternal sired lambs had 5% more iron than Merino and terminal sired lambs, and lambs of groups slaughtered at a later age generally had a higher zinc concentration. In conclusion, both genetic and non-genetic factors have a significant effect on the iron and zinc contents of lamb meat.