Mercier, J., Cinq-Mars, D., Berthiaume, R., Faucitano, L. and Girard, C. L. 2015. Effects of dietary total non-structural carbohydrates and folic acid and vitamin B₁₂ supplement on growth and meat quality of yearling steers in a forage-based beef production system. Can. J. Anim. Sci. 95: 281-291. Thirty-two spring calving cows [760±91 kg body weight (BW)] and calves (44±4.5 kg BW) were assigned to eight blocks of four cows and their calves each according to parity and calving date. Within each block, two cows were fed a low total non-structural carbohydrate (TNC) diet, while the two others were fed a high TNC diet. Within each diet, cows were administered either no vitamins or weekly intramuscular injections of 160 mg of folic acid plus 10 mg of vitamin B₁₂. Calves were slaughtered at 305±9 d. Neither TNC concentration nor vitamin supplementation affected (P>0.10) milk yield but the vitamin supplementation increased (P=0.002) milk concentrations of vitamin B₁₂. There was no treatment effect on calf performance, or carcass and meat characteristics (P>0.10) except for collagen concentrations and shear force measurements in the longissimus lumborum muscle, which had a tendency to be decreased (P≤0.06) by the vitamin supplement. In the present study, differences in forage TNC concentrations did not influence cow and calf performance. Moreover, folic acid and vitamin B₁₂ supplements were shown to have little impact in this study on growth of beef cattle.