Feeding ferric ammonium citrate to decrease the risk of sulfur toxicity: effects on trace mineral absorption and status of beef steers.

The objective of this study was to determine the effects of adding ferric ammonium citrate (FAC; 300 mg ferric Fe/kg DM) to a 0.51% S diet on diet digestibility, mineral balance, and 56-d performance of steers fed a high concentrate diet. Angus-crossbred steers (n = 18) were randomly assigned to 1 of 3 treatments: 1) control diet (0.21% S; CON), 2) CON + sodium sulfate (0.51% S; high S [HS]), and 3) the HS diet + 300 mg of ferric Fe from FAC/kg DM (0.51% S; HS+Fe). This study included 2 phases, 1) a metabolism trial (d -1 to 20) and 2) a 56-d feedlot trial (d 22 to 79). In phase 1, 2 groups of 9 steers (370 ± 9.5 kg) were adapted to diet (10 d) and metabolism stalls (5 d), and following the adaptation period, a 5-d total collection of feces and urine was conducted. Feed offered and refused was recorded daily, and diet digestibility and retention of Cu, Fe, Mn, and Zn was determined. In phase 2, steers (384 ± 11.9 kg) were individually fed their respective diet in feedlot pens for 56 d and ADG was determined. From each steer, jugular blood and a liver biopsy were collected on d -1, 41, and 72 and d -1 and 72, respectively, for mineral content. Ruminal hydrogen sulfide concentrations (n = 18) were determined on d -1, 9, 23, 31, 41, 51, 61, and 72. In phase 1, DMI (P = 0.02), fecal output (P = 0.06), and intake of Cu, Mn, and Zn (P ≤ 0.04) were less in steers consuming the high S diets than CON, but DM and OM digestibility and urine excretion of minerals were not different (P ≥ 0.12) due to treatment. As a percent of intake, urinary excretion of Cu tended (P = 0.07) to be greater in the HS steers than the CON and HS+Fe steers, which did not differ (P = 0.74). In phase 2, BW, ADG, and G:F were not different (P ≥ 0.29) due to treatment, but DMI was lesser (P < 0.01) in the HS+Fe steers than CON and HS steers, which did not differ (P = 0.13). Ruminal hydrogen sulfide concentrations were greater (P < 0.01) in the steers fed high S diets than CON but were not different (P = 0.86) among the high S diets. Plasma Cu, Fe, and Zn concentrations were not different (P ≥ 0.27) due to treatment on all days. Final liver Cu concentrations were lesser (P < 0.01) in the steers fed high S diets compared with the CON, while liver Fe, Mn, and Zn concentrations did not differ (P ≥ 0.28) among treatments. In conclusion, adding Fe to a high S diet did not affect DM or OM digestibility or trace mineral absorption and status of steers relative to the HS diet alone.