Background 

High sulfur (S) diets can decrease growth and carcass performance of feedlot cattle; however, little to no information is available regarding S and its effects on meat quality. In the rumen, the production of hydrogen sulfide (H₂S) from dietary S peaks within 10 to 35 days of when cattle start consuming a high S diet. Research suggests that high amounts of H2S may be related to the development of oxidative stress by depleting body antioxidants, such as glutathione (GSH). Previously, it was noted that steers consuming a high S diet had an oxidized-to-reduced GSH ratio of 28%, a ratio greater than 10% is indicative of oxidative stress, but when vitamin C (VC) was included in the high S diet the ratio was decreased to 7%. Bolstering the antioxidant capacity during the initial period of high S exposure may limit the development of oxidative stress and the subsequent effects on performance and meat quality. Vitamin C is known to regenerate GSH and vitamin E to their reduced forms. However, due to the ability of cattle to synthesize VC in the liver, no daily requirement for the vitamin has been established. Other researchers have noted a decrease in plasma VC during the finishing period, and supplementing VC during the finishing period increased marbling score and ribeye area (REA). Previously research reported that steers consuming a 0.55% S diet for 149 days showed a decreased proportion of the 76-kDa subunit of calpain-1 but the addition of 10 g VC∙steer-¹∙day^-1 to a 0.55% S diet increased the 76-kDa subunit of calpain-1 to values comparable with the 0.22% S treatments.

The objective of this study was to examine differential timing of VC supplementation during the finishing period (for the first 56, 90, or 127 days) on growth performance, carcass traits, and meat quality of steers receiving a 0.31 or 0.59% S diet.

Methodology 

Angus steers (n = 42) were sorted into pens by initial BW (304 ± 13 kg) and each pen was randomly assigned to 1 of 7 treatments (6 steers/pen, 1 pen/treatment), including a high S (0.59% S) control (HS CON), HS CON + 10 g VC/steer/day for the first 56 days (HS VC56), 90 days (HS VC90), or the entire 127 day finishing period (HS VC127), and a low S diet (LS, 0.31% S) + 10 g VC/steer/day for the first 56 days (LS VC56), 90 days (LS VC90), or 127 days (LS VC127). Intake data was collected on each individual, thus steer was used as the experimental unit. Jugular blood (plasma VC and GSH concentrations) and ultrasound measures were taken from each steer prior to feeding on day 0, 56, 90, and 127, and liver biopsies were collected on day 121 or 122. Steers (n = 40) were harvested on day 127, and carcass data and Rib-sections (7.62 cm thick) were collected. Using the collected Rib sections, the following measures were conducted:  ultimate pH, 7-day retail color display, Warner-Bratzler shear force, calpain-1 autolysis, troponin T and desmin degradation, and collagen, mineral and proximate content. 

Findings  

The interaction of treatment by month for dry matter intake was significant. Dry matter intake decreased between day 91 and 127 for all treatments except the HS VC127 and LS VC56 (Table 1). Plasma VC concentrations of the low S steers tended to be less (P = 0.08) than the high S steers; however, total (P = 0.06) and reduced (P = 0.03) plasma GSH concentrations were greater in the high S steers supplemented with VC than HS CON. Liver Cu, Mn, and Zn concentrations were not different due to treatment (P ≥ 0.14). Within the low S diets liver Fe showed a quadratic response (P = 0.05) to the days of VC supplementation, being greatest in the LS VC90 steers. Marbling score, Ribeye area, kidney, pelvic and heart fat and quality grade were not different (P ≥ 0.19) due to treatment; but high S steers had less (P = 0.05) back-fat compared to the low S steers. The high S control steers tended (P = 0.10) to have a greater percentage of USDA Yield Grade 1 and Select carcasses compared to the high S steers supplemented with VC.

Sulfur content of steaks was greater in the high S steers (P = 0.04). No differences were noted in shear force, percent moisture, fat content and ultimate pH (P ≥ 0.12) of the steaks due to treatment. L* values were not different by treatment (P ≥ 0.57). a* and b* (P ≤ 0.05) values were greater in the low S treatments than the high S treatments, but not different due to VC supplementation (P ≥ 0.11). Steers fed the high S diet showed a greater (P ≤ 0.05) percentage of the 80-kDa (intact) subunit and a lesser percentage of the 76-kDa (fully autolyzed) subunit of calpain-1 than the low S steers (Figure 1). Within the high S diet, increasing the days of VC consumption linearly decreased (P = 0.05) the percentage of the 80-kDa subunit of calpain-1, but the 76-kDa subunit was not different (P = 0.13). Alternately, in the low S diet, increasing the days of VC supplementation increased (P ≤ 0.05) the 80-kDa subunit of calpain-1 and decreased the 76-kDa subunit. Troponin T degradation (2 days postmortem) tended to be lesser (P = 0.08) in high S steers than low S, while degradation was not different due to treatment on day 7 (P ≥ 0.55). Desmin degradation was not affected by dietary treatment (P ≥ 0.21).

Implications  

These results continue to support the conclusion that increasing dietary S to cattle diets decreases growth performance and calpain-1 autolysis. However, limited effects of dietary S and supplemental VC were noted on carcass traits and meat quality in this study. Additionally, the regenerative relationship between VC and GSH may indicate VC supplementation could provide a sparing mechanism for GSH if cattle experience oxidative stress when consuming high S diets.