Visual Marble Score as a Predictor of Intramuscular Fat for the Genetic Improvement of Eating Quality in Lamb

Abstract

Marbling refers to the small flecks of fat deposits between muscle fibres and is used as a subjective measure of intramuscular fat (IMF) – a key determinant of eating quality in red meat. In lamb, there is limited literature describing visual scoring guides and the trait correlations with other carcase traits. The objectives of this study were to establish a visual scoring system for marbling in lamb, estimate genetic parameters for the trait and estimate relationships with other eating quality and carcase traits. A 5-point visual marble score guide was constructed, which was highly correlated to the corresponding IMF of each sample (r = 0.99). To estimate genetic parameters, 1,120 loin samples were scored for visual marbling, with an average score of 3.01 (± 0.68, SD). On a phenotypic level, a 1 unit score increase was associated with a significant increase in IMF by 0.83 ± 0.04% (p < 2e-¹⁶). The heritability estimate for visual marble score was 0.28 ± 0.09, and there was a high genetic correlation between visual marble score and IMF (r𝓰 = 0.93 ± 0.08). While more data are required for better genetic parameter estimates, these results indicate that visual marble score is an accurate phenotypic and genetic predictor of IMF in lamb. Therefore, there is potential for the use of visual marble scoring in lamb for the genetic improvement of eating quality in the interim period before a more rapid and accurate technology is commercially available to measure IMF.