Vitamin A regulates intramuscular adipose tissue and muscle development:promoting high-quality beef production

During growth in cattle,the development of intramuscular adipose tissue and muscle is dependent upon cell hyperplasia(increased number of adipocytes)and hypertrophy(increased size of adipocytes).Based on the results of previous studies,other adipose tissue depots(e.g.,perirenal and subcutaneous)develop from the fetal stage primarily as brown adipose tissue.The hyperplastic stage of intramuscular adipose is considered to develop from late pregnancy,but there is no evidence indicating that intramuscular adipose tissue develops initially as brown adipose tissue.Hyperplastic growth of intramuscular adipose continues well into postweaning and is dependent on the timing of the transition to grain-based diets;thereafter,the late-stage development of intramuscular adipose tissue is dominated by hypertrophy.For muscle development,hyperplasia of myoblasts lasts from early(following development of somites in the embryo)to middle pregnancy,after which growth of muscle is the result of hypertrophy of myofibers.Vitamin A is a fat-soluble compound that is required for the normal immunologic function,vision,cellular proliferation,and differentiation.Here we review the roles of vitamin A in intramuscular adipose tissue and muscle development in cattle.Vitamin A regulates both hyperplasia and hypertrophy in in vitro experiments.Vitamin A supplementation at the early stage and restriction at fattening stage generate opposite effects in the beef cattle.Appropriate vitamin A supplementation and restriction strategy increase intramuscular adipose tissue development(i.e.,marbling or intramuscular fat)in some in vivo trials.Besides,hyperplasia and hypertrophy of myoblasts/myotubes were affected by vitamin A treatment in in vitro trials.Additionally,some studies reported an interaction between the alcohol dehydrogenase-1C(ADH1C)genotype and vitamin A feed restriction for the development of marbling and/or intramuscular adipose tissue,which was dependent on the timing and level of vitamin A restriction.Therefore,the feed strategy of vitamin A has the visible impact on the marbling and muscle development in the cattle,which will be helpful to promote the quality of the beef.

Vitamin A supplementation downregulates ADH1C and ALDH1A1 mRNA expression in weaned beef calves

Our previous studies demonstrated that oral vitamin A supplementation during late-stage pregnancy and the neonatal stage enhances birth weight,growth performance,and mRNA expression related to muscle and preadipocyte development in beef cattle.The alcohol dehydrogenase 1C(ADH1C)c.-64T>C genotype also correlated with vitamin A concentration in beef production.This study aimed to investigate the effects of vitamin A supplementation on the muscle development and vitamin A metabolism in weaned beef calves with different ADH1C genotypes.Twenty male calves(90 d of age;initial BW:89.03 kg[SD 8.60])were stratified according to ADH1C genotype and vitamin A treatment(duration:3 months)and randomly assigned to 4 groups with a 22 factorial arrangement.Vitamin A treatments included the following:control(10,000 IU/kg of as-fed,a.TT type;b.TC type);treatment(40,000 IU/kg of as-fed,c.TT type;and d.TC type).Parameters including BW,FI,blood,longissimus dorsi muscle,and liver status during the experimental period were analyzed using the generalized linear model(GLM)procedure and Tukey's test by SAS 9.4 program.Serum vitamin A was significantly increased(P<0.05)in the vitamin A treatment group at 4 and 6 months of age.TT type calves showed higher serum vitamin A concentration(P<0.05)than the TC type calves.Serum triglyceride and non-esterified fatty acid(NEFA)levels increased(P<0.05)in the treatment group compared with the control at 6 months of age.However,BW,ADG and FI showed no differences between the groups.In addition,mRNA expression in longissimus dorsi muscle revealed upregulation of paired box 7(PAX7)(P<0.05)after the vitamin A treatment period based on biopsy results.Both ADH1C and aldehyde dehydrogenase(ALDH)1A1 mRNA expression was downregulated(P<0.01)by vitamin A supplementation.The TC type of ADH1C showed higher mRNA expression than the TT type.However,no effect was observed on adipogenic mRNA expression(preadipocyte factor-1[PREF-1],peroxisome proliferator-activated receptor gamma[PPARg],fatty acid binding protein 4[FABP4])in all groups.Our findings suggest that weaned calves treated with vitamin A may promote the storage of satellite cells by elevating PAX7 gene expression in the muscle.The TC type calves may show increased capacity for vitamin A metabolism,which can be used in genetically customizing feed management to maximize beef production in the calves.