Effects Of Vitamin A On Beef Quality Of Limousin×Luxi Crossbred Steers And Action Mechanisms

The effects of dietary vitamin A concentration on beef quality of Limousin X Luxi steers and its mechanisms were investigated in three experiments with randomized complete-block design. Sixteen 12 months old steers (BW: 306+ 14.2kg),sixteen 12 months old steers (BW: 309+ 13.7kg) and sixteen 24 months old steers (BW: 421 + 19.5kg) were divided averagely into four groups according to BW, and finished individually with the same basal diets for 90,180 and 90 days respectively. Four group steers were supplemented with 0, 1100, 2200 and 4400 IU/kg diet(dry matter) vitamin A respectively in the experiment. Results showed that 0 and 1100IU/kg diet vitamin A contents increased the intramuscular fat contents and improved marbling for all steers, also improved beef color, antioxidant ability, tenderness and WHC of longissimus dorsi(LD) and gluteus medius(GM), decreased back subcutaneous fat depths(BSFD) and beef drip loss(DL) significantly, and had no effects on the daily gain, feed utilization, eye muscle area, carcass yield, percentage of mesentery fat(MF) weight to slaughter weight, and beef chemical compositions for 12 months old steers. However, the diets without additional vitamin A more than 150 days depressed the effects of beef quality improvement and also influenced the steers health. The 1100IU/kg diet vitamin A supply was the best to improve beef quality and had no the negative effect on the steers health in the study. Different concentrations of Vitamin A in diet influenced significantly the contents of insulin, glucagons, GH, T3 and cortisol in blood, the vitamin A and E concentrations in liver, serum, LD, GM, BSF and MF, the specific activity of LPL,HSL and FAS in LD, GM, BSF and MF, the mRNA contents of ACC, FAS, HSL LPL and PPARγ in LD and GM, not the retinoic acid concentrations in liver, serum, LD, GM, BSF and MF, and the cAMP content in LD, GM, BSF and MF. The effects of vitamin A to adipogenesis were regulated through the changes of insulin secretion, LPL and HSL activities, and mRNA content of ACC, FAS and PPARγ. The specific activity of LPL and HSL were not regulated by cAMP-dependent phosphorylation and dephosphorylation pathway.The adipocytes obtained from back subcutaneous adipose tissues of 12 months Limousin X Luxi crossbred bulls were cultured in vitro with differential inducing culture solution which were replaced with serum-free culture solution containing retinoic acid, retinol or retinyl palmitate(50ug/dl) after 48h. The concentrations of the additaments in culture solution were mensurated per 12h during 96h. Results showed that concentrations of retinoic acid and retinol decreased rapidly at the beginning of the culture, and then concentrations of retinoic acid decreased slowly after cells were cultured for 36h, however, concentrations of retinol increased in 60h after the cells were cultured for 12h and then declined quickly again. The concentration of retinoic acid in culture solution had exponential correlation to culture time, the equation is y(concentration of retinoic acid in culture solution, μg/dl)=0.4122x(culture time,h)~-0.8286 (R2=0.8959). Concentration of retinyl palmitate in culture solution always decreased slowly and had linear correlation to culture time, the equation is y(concentration of retinyl palmitate in culture solution,ng/dl)= -0.0329x(culture time,h)+ 0.4653(R2=0.9204).