Neonatal vitamin A injection promotes cattle muscle growth and increases oxidative muscle fibers

Background:Vitamin A and its metabolite,retinoic acid (RA),are important regulators of cell differentiation and organ morphogenesis.Its impact on beef cattle muscle growth remains undefined.Method:Angus steer calves were administrated with 0 (control) or 150,000 IU vitamin A (retinyl palmitate in glycerol,i.m.) per calf at birth and 1 month of age.At 2 months of age,a biopsy of the Biceps femoris muscle was obtained to analyze the immediate effects of vitamin A injection on myogenic capacity of muscle cells.The resulting steers were harvested at 14 months of age.Results:Vitamin A administration increased cattle growth at 2 months.At 2 months of age,Vitamin A increased PAX7 positive satellite cells and the expression of myogenic marker genes including PAX7,MYF5,MYOD and MYOG.Muscle derived mononuclear cells were further isolated and induced myogenesis in vitro.More myotubes and a higher degree of myogenesis was observed in vitamin A groups.Consistently,vitamin A increased Latissimus dorsi (LD) muscle fiber size at harvest.In addition,vitamin A increased the ratio of oxidative type Ⅰ and type ⅡA fibers and reduced the glycolic type ⅡX fibers.Furthermore,we found that RA,a key bioactive metabolite of vitamin A,activated PPARGC1A promoter,which explains the upregulated expression of PPARGC1A in skeletal muscle.Conclusion:Vitamin A administration to neonatal calves enhanced postnatal muscle growth by promoting myogenesis and increasing satellite cell density,accompanied with a shift to oxidative muscle fibers.