Abstract
Intramuscular fat (IMF) content affects eating and nutritional quality of lamb meat. Muscle density measured by computer tomography is an in vivo proxy measure of IMF content that affects eating and nutritional quality of lamb meat. Lambs sired by high muscle density (HMD) or low muscle density (LMD) rams, selected for slaughter on commercial criteria were measured for meat quality and nutritional traits. A restricted maximum likelihood model was used to compare lamb traits. Additionally, regression analysis of sire estimated breeding value (EBV) for muscle density was performed for each meat quality trait. Muscle density EBV had a negative regression with IMF content (P < 0.001). For each unit increase in muscle density EBV, there was a significant decrease in loin (−1.69 mg/100 g fresh weight) and topside IMF (−0.03 mg/100 g fresh weight). Muscle density EBV had a negative regression with grouped saturated and monounsaturated fatty acids concentration (and monounsaturated proportion P < 0.001). Muscle density EBV had a negative regression with loin sensory traits tenderness, juiciness and overall liking and many novel tenderness sensory traits measured (P < 0.05). Selecting for LMD EBV increased IMF content and favourable meat eating quality traits. In contrast, sire muscle density EBV had a positive regression with loin polyunsaturated:saturated fat ratio and grouped polyunsaturated proportion traits (including total polyunsaturated proportion, total omega-6 (n-6) and total omega-3 (n-3) fatty acids (P < 0.001). This is explained by the fact that as sire muscle density EBV increases, polyunsaturated fatty acid proportion increases and the proportion of saturated and monounsaturated fatty acid content decreases. Muscle density EBV had a positive regression with shear force and the novel toughness sensory traits (P < 0.05). Selection for HMD EBV's increased shear force and toughness traits, which is unfavourable for the consumer. Low muscle density sired meat had higher meat colour traits chroma/saturation (+0.64, SD 2.30, P = 0.012), redness (+0.52, SD 1.91, P = 0.012) and yellowness (+0.31, SD 1.49, P = 0.08) compared to HMD sired meat. Selection for LMD could be used within a breeding programme to increase IMF content and enhance both meat colour and improve eating quality parameters.
Highlights
Selection for increased lean and decreased fat has led to lower fat content in lamb meat
Selecting for rams with low muscle density estimated breeding values enhances lamb meat eating quality by increasing intramuscular fat, decreasing shear force, improving sensory traits relating to tenderness and increases colour traits
Mean muscle density recorded at the fifth lumbar vertebrae (LV) of high muscle density (HMD) and low muscle density (LMD) ram groups differed by 3 SD
Summary
Selection for increased lean and decreased fat has led to lower fat content in lamb meat. Intramuscular fat (marbling) is beneficial for meat eating quality. Muscle density is a novel in vivo proxy computer tomography trait for intramuscular fat. Selecting for rams with low muscle density estimated breeding values enhances lamb meat eating quality by increasing intramuscular fat, decreasing shear force, improving sensory traits relating to tenderness and increases colour traits (saturation, redness and yellowness). Muscle density could be used within a terminal sire breeding programme to improve lamb meat eating quality. Low CT muscle density could be used as a proxy for increased IMF and improved meat quality. This study was designed to test the hypothesis that selecting rams for CT scanned low muscle density (LMD) will increase progeny IMF content and improve meat eating quality traits without changing the nutritional quality
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