Effect of varying concentrations of vitamin C on performance, blood metabolites, and carcass characteristics of steers consuming a common high-sulfur (0.55% S) diet.

The objective of this study was to examine the effects of vitamin C (VC) supplementation for an average of 102 d before harvest on finishing performance and blood metabolites of steers receiving a 40% dry distillers grains plus solubles diet (0.55% S). Yearling, Angus-cross steers (n = 140) were blocked by initial BW (432 ± 25.5 kg), stratified within blocks by intramuscular fat (3.6% ± 0.30%) determined by ultrasonography, and assigned to treatments (5 steers/pen, 7 pens/treatment). Treatments included 1) no VC control (CON), 2) 5 g VC • steer(-1) • d(-1) (5VC), 3) 10 g VC • steer(-1) • d(-1) (10VC), and 4) 20 g VC • steer(-1) • d(-1) (20VC). Jugular blood was collected from 2 steers/pen before feeding at the beginning and end of the 102-d study, and steers were harvested by block on 3 separate dates (d 91, 105, and 112). Sulfur intake linearly decreased (P = 0.01) as VC inclusion increased (59.2, 57.7, 57.0, and 54.8 ± 0.79 g S • steer(-1) • d(-1) for CON, 5 VC, 10 VC, and 20 VC, respectively). The CON cattle had greater (P < 0.01) DMI than the VC-supplemented cattle. Inclusion of VC did not influence ADG or final BW, resulting in a tendency for a linear increase (P = 0.08) in G:F as VC inclusion increased (0.150, 0.152, 0.158, and 0.160 ± 0.004 for CON, 5 VC, 10 VC, and 20 VC, respectively). Ending (2 d before harvest) plasma ascorbate showed a quadratic effect (P < 0.05) because of lesser concentrations exhibited by 5 VC cattle (1,186 µg/L) compared with the CON (1,454 µg/L), 10 VC (1,304 µg/L), and 20 VC (1,436 µg/L; SEM ± 64.8) cattle. Ending plasma insulin concentrations of CON cattle tended (P = 0.07) to be less than the VC-supplemented cattle. Plasma glucose and NEFA concentrations were not affected (P ≥ 0.23) by VC inclusion. Hot carcass weight, 12th-rib back fat, marbling, and quality grade were not affected (P ≥ 0.27) by VC inclusion. Increasing VC inclusion linearly increased (P = 0.02) rib eye area (84.9, 86.5, 88.7, and 89.1 cm(2) ± 1.17 for CON, 5 VC, 10 VC, and 20 VC, respectively), corresponding to a linear decrease (P = 0.02) in yield grade with increasing inclusions of VC. A tendency (P = 0.06) for a quadratic effect on KPH was observed, in which values generally increased from CON (2.27%) to 5 VC (2.37%) to and 10 VC (2.39%), then decreased in 20 VC (2.20%). In conclusion, VC supplementation to a high-S diet for an average of 102 d before harvest has limited effects on blood metabolites but increased rib eye area and tended to increase feed efficiency of yearling steers.