Possible association of bovine chromosome 5 markers with growth and fat traits in Hereford cattle raised under extensive conditions

Bovine chromosome 5 has been widely studied because several QTLs have been detected there, in particular for growth and fat traits. Even though most of the beef is produced under pasture based conditions, only little research has focused on this kind of systems. Two QTL regions, neighboring the Myogenic factor 5 gene, and Insulin-like Growth Factor 1 (IGF1) gene, were selected. Within them, four BTA5 microsatellites (BP1, ETH10, IGF1 and RM029) were used to establish their association with growth and fat traits in a pasture based feeding system. The Estimated Breeding Values tested were: 400 (W400) and 600Days Weight (W600), Rib Eye Area (REA), Rib Fat, Rump Fat, and Intra Muscular Fat. For growth traits significant associations (p≤0.05) between BP1 and REA, and between IGF1 and W600, were detected. For fat traits significant association (p≤0.05) between ETH10 and Rib Fat and Rump Fat was detected. When considering a pair of closer marker genotypes, IGF1/ETH10 was significantly associated (p≤0.05) with W400 and W600. These results show that QTL for growth and fat traits that were previously reported in two regions of BTA5, are also expressed in a commercial pasture based system, where animals are not always fed to express their maximum genetic potential.