304 - Effects of Supplementing Phix-up® on Productive, Physiological, and Rumen Responses of Feedlot Cattle Consuming a Corn-based Finishing Diet

This experiment (d -14 to 118) compared rumen pH, productive, and physiological responses in finishing cattle supplemented or not with a rumen-buffering agent (pHix-up^®; Timab, Dinard, France). Angus-influenced yearling cattle (58 heifers and 62 steers) were ranked by sex and body weight (BW) and allocated to 4 groups of 30 animals each (d -14). Groups were housed in 1 of 4 drylot pens equipped with GrowSafe automated feeding systems, and assigned to receive a corn-based diet containing monensin, and with the inclusion of pHix-up^® at 0.00% (control) 0.25%, 0.50%, or 0.75% (d 0 to 118). Cattle BW was recorded twice monthly (d -14 to 118), and blood samples were collected on d 0, 28, 56, 84 and 112. Hair samples from the tail-switch were collected on d 0, 56 and 112. Cattle were slaughtered on d 119. Eight rumen-cannulated steers were also assigned to this experiment (d 42 to 98), with 2 steers housed with each group in a replicated 4 × 4 Latin Square design (4 periods of 14 d). Rumen pH was measured on d 7 and 14 of each period at 0800h, 1200h, 1600h and 2000h. No treatment effects were noted (P ≥ 0.13) for cattle BW gain, feed intake, and feed efficiency. Inclusion of pHix-up^® linearly increased (P < 0.01) plasma Mg concentrations and tended to linearly decrease (P = 0.09) plasma haptoglobin concentrations. Cattle receiving pHix-up^® had greater (P < 0.01) mean plasma cortisol concentrations compared with non-supplemented cattle. Hair cortisol concentration linearly decreased (P < 0.01) as pHix-up^® inclusion increased on d 112 (treatment × day interaction; P = 0.02). In rumen-cannulated steers, pHix-up^® inclusion linearly increased (P = 0.03) mean rumen pH. Collectively, pHix-up^® supplementation improved rumen pH and modulated stress-related physiological responses in finishing cattle, but without improving their productive responses.