Effects of duration of vitamin C supplementation on growth performance, carcass traits, and protein degradation of the longissimus thoracis of steers fed a 0.31 or 0.59% sulfur diet

Abstract Text: Angus steers (n = 42) were allotted equally to 7 pens with individual feed intake monitoring technology by BW (304 ± 13 kg), and fed 1 of 7 diets:  4, high-S (0.59% S) diets, supplemented with 10 g vitamin C (VC)∙steer^-1∙d^-1 for 0 (HSCON), 56 d (HSVC56), 90 d (HSVC90), or 127 d (HSVC127) and 3, low-S diets (LS, 0.31% S), supplemented with 10 g VC∙steer^-1∙d^-1 for 56 d (LSVC56), 90 d (LSVC90), or 127 d (LSVC127). Jugular blood (d 0, 56, 90, 127) and liver (d 121 or 122) were collected from all steers. Steers (n = 40) were harvested on d 128, and carcass data and rib-sections were collected. Steer was the experimental unit and data were analyzed using Proc Mixed. Final BW (P < 0.01), ADG (P < 0.01), and DMI (P = 0.09) were greater in LS steers than HS steers, but G:F was not affected (P = 0.41) by treatment. Total (P = 0.06) and reduced (P = 0.03) plasma glutathione (GSH) concentrations were greater, and the ratio of oxidized-to-reduced liver GSH was lesser (P < 0.01), in VC-fed HS steers compared with HS CON. Ribeye area and marbling score were not affected by diet (P ≥ 0.33), but LS steers had greater (P = 0.05) back-fat than HS steers. a* and b* values were greater (P ≤ 0.05) in LS steaks than HS steaks over 7 d. Steaks from  HS steers had greater total (P = 0.02), soluble (P = 0.06), and insoluble (P = 0.06) collagen (d 2) than steaks from LS steers. Steaks (d 2) from steers fed the HS diet had a greater (P < 0.01) and lesser (P = 0.04) percentage of the 80-kDa and 76-kDa subunit of calpain-1, respectively, than the LS steers. Adding VC to the HS or LS diets linearly decreased the 80-kDa subunit (P = 0.03) and 76-kDa subunit (P = 0.04) of calpain-1, respectively. Troponin-T (TT) degradation 2 d postmortem tended to be greater (P = 0.08) in LS steers than HS steers, while TT 7 d postmortem did not differ (P ≥ 0.55) by treatment. In conclusion, improved GSH indices in the VC-supplemented HS steers may be supporting increased activation of calpain-1 compared with steers fed HS alone. It appears that high S diets may negatively affect the rate, but not extent of longissimus thoracis protein degradation.

Keywords: Beef cattle, sulfur, vitamin C