Effects of feeding ferric citrate on methane production and nutrient and energy balance in growing beef steers

We determined the effects of ferric citrate supplementation on energy partitioning, methane produc-tion, and nutrient balance in growing beef steers. Angus steers (n = 8; initial BW = 363 ± 30.4 kg) were used in a replicated 4 × 4 Latin square design experiment. Treatments were as fol-lows: (1) 0 mg of ferric citrate (F0, control); (2) 250 mg Fe/kg DM as ferric citrate (F250); (3) 500 mg Fe/kg DM as ferric citrate (F500); or (4) 750 mg Fe/kg DM as ferric citrate (F750). After a 16-d diet adaptation period, di-etary treatment, orts, feces, and urine were collected and composited over a 5-d collection period. On d 3 of each collection period, gas exchange was measured using indi-rect calorimetry headboxes. Methane energy loss tended to decrease quadratically, with F0 and F750 steers hav-ing greater methane energy losses than F250 and F500 steers. Subsequently, ME decreased linearly, and ME as a proportion of GE intake tended to decrease, with increas-ing concentrations of ferric citrate. Retained energy and retained energy as a proportion of GE intake tended to decrease linearly as ferric citrate concentration increased. In addition, fecal nitrogen excretion tended to increase as ferric citrate concentration increased. Collectively, these findings suggest that ferric citrate could slightly decrease CH 4 energy losses at concentrations below 500 mg. None-theless, linear decreases in ME and retained energy suggest that ferric citrate inclusion may have detrimental effects on energy balance that limit its application in growing beef steers. Therefore, potential environmental benefits are negated by the decrease in energetic efficiency. Over-all, these findings do not support the use of ferric citrate for CH 4 mitigation.