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Abstract
BackgroundVitamin 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.MethodAngus 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.ResultsVitamin 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.ConclusionVitamin 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.
Highlights
Vitamin A and its metabolite, retinoic acid (RA), are important regulators of cell differentiation and organ morphogenesis
Our previously study showed that administration of vitamin A at birth increased weaning weight of beef cattle [28], and the aim of this study was to explore the effects of neonatal vitamin A administration on bovine muscle growth and muscle fiber type composition
Vitamin A administration upregulates the expression of myogenic genes Our previously study showed that vitamin A administration at birth strongly increased beef cattle growth [28], which was mostly likely through promoting muscle growth because muscle accounts close to 50% of body weight and the hip length was not affected
Summary
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. Postnatal muscle growth is achieved mainly by hypertrophy of existing myofibers [5], Skeletal muscle is composed of different types of fibers. Type I is a slow-twitch, oxidative fiber. Type IIA is a fast oxidative-glycolytic fiber. Type IIX is a fast-twitch, glycolytic fiber for beef cattle [7, 8]. The muscle fiber-type composition is an important factor in determining meat quality. Glycolytic muscle fibers accumulate greater amount of lactate during the postmortem stage [9], which is negatively associated with water holding capacity [10]. Muscles with high proportion of type IIX fibers had high lactate content and showed low muscle pH45min [11]. Peroxisome-proliferator-activated receptor-γ coactivator-1 (PGC-1α) is a transcriptional co-activator abundant in skeletal muscle, which activates
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