The effect of supplemental vitamin C on performance, antioxidant capacity, carcass characteristics, and meat quality of steers fed high sulfur finishing diets.

摘要

The incorporation of ethanol industry co-products, such as dried distillers grains plus solubles, to feedlot diets in the United States may be inadvertently exposing cattle to high amounts of dietary sulfur. High sulfur diets have repeatedly been reported to decrease growth and carcass performance, health, and copper status; however, little to no information is available concerning the implications that high sulfur diets have on the antioxidant capacity or meat quality of cattle. Thus, the subsequent research trials were designed to: 1) examine the impacts of high dietary S on diet digestibility and macro and micro mineral absorption and retention, 2) determine the effect of supplementing a rumen-protected vitamin C during the entire finishing period of steers on growth performance, trace mineral status, antioxidant capacity, carcass characteristics, and meat quality, 3) determine the optimal dose of supplemental vitamin C within a high sulfur diet on growth performance, blood metabolites, carcass characteristics, and meat quality, and 4) identify the influence of timing of vitamin C supplementation during the finishing period on growth performance, plasma vitamin C and glutathione concentrations, and carcass characteristics. Within our first research objective, the consumption of a high sulfur diet for at least 28 days decreased copper, manganese, and zinc retention in steers. These trace minerals are components of antioxidant enzymes, suggesting a lesser availability of these minerals may decrease antioxidant capacity of the animal. Within our second research objective, supplementing vitamin C (10 g per steer per day) to calf-fed steers consuming a high sulfur (0.55%) diet for 149 days prevented a decline in circulating ascorbate throughout the finishing period and increased marbling scores from high Select to low Choice compared to the high sulfur, non-vitamin C supplemented steers. The inclusion of vitamin C to the high sulfur diet prevented the ratio of oxidized-to-reduced liver glutathione from rising above the oxidative stress threshold of 10%, while a ratio of 28% was observed in the non-supplemented high sulfur steers, indicating some oxidative stress was occurring. In postmortem muscle of these calf-fed steers, the ante-mortem supplementation of vitamin C increased the presence of the fully autolyzed (76-kDa) subunit of calpain-1, an enzyme involved in the tenderization process, and increased the polyunsaturated fatty acid content of the longissimus thoracis compared to the un-supplemented high sulfur steers. In yearling steers, increasing the dose of supplemental vitamin C (0, 5, 10 or 20 g per steer per day) in a high sulfur (0.55%) diet linearly decreased dry matter intake, tended to increase feed efficiency, and increased ribeye area. In postmortem muscle, increases in vitamin E and iron and lesser meat lightness values were noted within the vitamin C supplemented treatments compared to the un-supplemented controls, while no differences in calpain-1 autolysis, shear force, or fatty acid profile of the longissimus thoracis were observed. Finally, the addition of vitamin C (10 g per steer per day) for the first 56, 90, or 127 days (entire finishing period) of finishing to calf-fed steers consuming a low (0.31%) or high (0.59%) sulfur diet showed limited effects on performance and carcass traits. The findings of our experiments yielded conflicting results of how supplemental vitamin C is impacting finishing steer growth performance, carcass traits, and meat quality; however, these differences may be attributed to individual animal variability or differing genetics of the steers used in these studies. Further research is warranted to better understand the mechanism by which vitamin C supplementation to finishing cattle is influencing circulating ascorbate concentrations, marbling potential, and ribeye area.