Examination of the expression of genes and proteins controlling M. longissimus thoracis et lumborum growth in steers

The first study conducted investigated the effect of sire breed and genetic merit for growth potential of the transcriptional regulation of the somatotropic axis followed by a proteomic approach to assess differentially abundant proteins. Following this, a second study was set up to examine the compensatory growth phenomena in cattle which aimed to investigate the effect of feed restriction and feed realimentation on animal production and physiological variables and the residual effects on meat quality attributes. The final chapter in this thesis focused on the transcriptional regulation of compensatory growth in M. longissimus thoracis et lumborum in crossbred Aberdeen Angus steers. It is evident from this thesis that genetic merit for growth potential in cattle is under molecular control and chapters 3 and 4 offer revealing insight into the somatotropic axis and glucose metabolism. RNAseq, a highly sensitive approach to transcriptome sequencing, was used to conduct the transcriptional sequencing analysis in chapter 7. During the differential feeding period, gene pathways relating to lipid metabolism were significantly different between the two treatments and consistent with plasma leptin concentrations and ultrasonically scanned fat depth data (chapter 5). During the realimentation period, when previously restricted steers were experiencing compensatory growth, the TGF-βR1 gene involved in the TGF-β signalling pathway, a negative regulator of growth, was down-regulated in expression. The results obtained from this study offer a novel insight into key regulatory genes and pathways controlling compensatory growth in skeletal muscle of cattle which following appropriate validation may be incorporated into genomically assisted selection strategies for beef cattle. Overall, this thesis has offered significant insight into key pathways regulating growth in cattle such as the somatotropic, glycolytic and TGF-β signalling pathways