Abstract
This study elucidated the effects of dosage-dependent guanidinoacetic acid (GAA) supplementation on growth performance, muscle responses, and carcass characteristics in finishing beef steers. Thirty crossbred Red Angus beef steers (395 ± 28.09 kg) were randomly assigned one of three treatments during a 146-d feedlot study: basal diet without GAA supplementation (CONTROL), 1g of GAA per 100 kg of body weight (BW) daily (LOWGAA), and 2 g of GAA per 100 kg of BW daily (HIGHGAA). Individual feed intake was monitored daily, growth performance parameters were collected every 28 d, and longissimus muscle (LM) biopsies occurred every 56 d. In biopsied LM, greater (P = 0.048) mRNA expression of IGF-1 was observed in LOWGAA steers on day 112 compared to the CONTROL group. LOWGAA steers also exhibited greater expression of myosin heavy chain (MHC) I compared to CONTROL steers (P < 0.05) and MHC IIA compared to both CONTROL and HIGHGAA treatment groups (P < 0.01) on day 112. GAA supplementation resulted in no change in carcass characteristics, serum and LM tissue metabolites, LM composition, and Warner-Bratzler shear force values (P > 0.05). Data collected from this study demonstrate the influence of GAA supplementation on the gene expression of MHC isoforms and their role in skeletal muscle growth, differentiation, and muscle fiber-typing.