508 Effects of starch content of the concentrate on growth performance, temperament and carcass traits of finishing bison

Abstract Yearling bison bulls [n = 48; commercial Wood × Plains, 435 ± 13.4 kg body weight (BW)] were used in a 156-d feeding trial to evaluate the effects of the starch content in the concentrate on growth performance, gain-to-feed ratio (GF), temperament, and carcass traits. Bison were homogenously distributed into 12 pens (4 bulls/pen) based on BW, and each pen randomly assigned (n = 6) to receive either a high-starch (HS; 51.4% dry matter basis, DM), or moderate-starch (MS; 25.8% DM) concentrate, alongside free access to water and grass hay bales. The amount of feed delivered to each pen and orts were recorded to estimate dry matter intake (DMI) for each ingredient. Bison were weighed on d 1, 28, 60, 116, and 156 to monitor average daily gain (ADG) and GF. When handled for weighing, exit speed from the chute was determined as a measure of their temperament. On d 156, bison were transported to a slaughterhouse where back fat thickness, carcass grade, and ribeye area were determined. The HS bison bulls had reduced DMI for both grass hay (P = 0.04) and concentrate (P < 0.01) compared with MS. The HS bulls had a greater (P < 0.01) chute exit speed than MS. Both MS and HS had similar (P > 0.10) final BW, ADG, GF, and proportion of hay and concentrate inclusion in the diet. Back fat thickness, ribeye area, and proportion of carcass grades were not different (P > 0.10) between MS and HS. These findings suggest that finishing bison bulls reduced their feed intake in response to a high percentage of starch in the concentrate, without affecting growth performance, GF, or carcass traits indicative of fat and muscle deposition, but with HS causing a more excitable temperament profile, typically associated to chronic stress.