Interpretive Summary: Evaluation of vitamin A status on myogenic gene expression and muscle fiber characteristics
By: Dr. Emily Taylor
A recent article published in the Journal of Animal Science used 30 yearling crossbred steers being fed a steam-flaked corn-based diet to evaluate the effects of dietary vitamin A supplementation on myogenic gene expression and skeletal muscle fiber characteristics during the finishing phase. Blood, longissimus muscle, and liver biopsies were used for immunohistochemical and mRNA analysis, while sera and liver samples were used to monitor circulating vitamin A and true vitamin A status.
The expression of myosin heavy chain (MHC)I, the intermediate fiber type (MHC-IIA) PPARg, and PPARd was reduced; however, an increase was observed as the trial continued. For each MHC, muscle fiber cross-sectional area increased. Total nuclei density decreased over time, while cells positive for Myf5 increase in density early in the feeding period. However, following the peak increase, authors did observe a decline in Myf5 positive cells and attributed this decline to the satellite cells fusing into fibers. In addition, the dual-positive (PAX7+Myf%) nuclei also peaked, with a similar decline as stated previously.
In conclusion, the data presented indicate that oxidative gene expression may be independent of vitamin A status. Expression of genes related to oxidative proteins was not impacted by the steers vitamin A status. Furthermore, animals deficient in vitamin A before trial initiation were able to maintain protein deposition in muscle as well as animals not deficient in vitamin A. The authors suggest further research should be conducted to evaluate similar parameters when using amounts of vitamin A in excess of nutritional requirements.