Effect of thyroglobulin gene polymorphism on the intramuscular fat content in cattle examined by x-ray computed tomography and Soxhlet methods

Intramuscular fat content or marbling represents a valuable beef quality trait and is an important determinant of palatability due to its contribution to juiciness and flavour. Meat which has little marbling may be dry and flavourless. Higher levels of intramuscular fat have been associated with increased tenderness, juiciness and flavour of beef (Thompson 2004). Whereas this feature is highly appreciated in some markets (by example Australia, China, Korea, Japan) breeders usually try to increase intramuscular fat deposition in cattle by nutrition. However, genetic factors have been shown to affect marbling in cattle. Thyroglobulin (TG) is a glycoproteic hormone synthesised in the thyroid gland and is the precursor of triiodothyronine (T3) and thyroxine (T4) hormones which influence lipid metabolism. T3 and T4 hormones have been associated with marbling in Wagyu cattle (Mears et al. 2001). The effect of a C/T single nucleotide polymorphism in the 5'-untranslated region of TG gene has been concluded to affect intramuscular fat content in cattle (Barendse 1999). High probability of positive association between the T allele of bovine TG gene and marbling was observed by Wood et al. (2006). Thyroglobulin mainly affects the fat content of longissimus dorsi muscle (LD) (Thaller et al. 2003).