410 Utilizing By-products to replace high moisture corn in a large pen trial: A circular economy strategy for finishing nellore bulls in a tropical feedlot system.

Abstract The United Nations defines a circular economy as one where markets encourage the reuse of products instead of discarding them and sourcing new materials. As a result, assessing waste by-products (‘opportunity feeds’) as part of beef cattle diets become an essential strategy to achieve sustainability in the global beef chain. In this context, we examined the incorporation of various by-products commonly utilized in Brazilian beef production by replacing high moisture corn (high and low energy diets). A total of 1,781 24-month-old Nellore bulls [382.3 ± 22.6 kg of body weight (BW; mean ± SD)] were assigned to 32 open dry lot pens (n=55/pen; 16 pens/treatment) in a complete block design (4 blocks set by initial BW) with ad libitum access to feed and water. The experimental feeding program consisted of adaptation (16 d), growing (27 d), and finishing phases (66 to 76 d). The treatments consisted of 2 levels of energy: Normal and Low energy (reduction of 18.4, 16.7, and 15.1 %, for adaptation, growing, and finishing diets, respectively). Diets were formulated to provide nutrients for an ADG of at least 1.5 kg, according to the LRNS. The energy level was modulated by replacing high moisture corn by sugar cane bagasse, citrus pulp, and soybean hulls. Dry matter intake was evaluated in a pen approach (considering 1-2% of feed refusals) as well as BW and all derivations index created by combining these variables. Initial carcass weight (used in the carcass gain and carcass feed conversion), was estimated by considering 50% of dressing. All statistical analyses were performed using SAS version 9.4 (SAS Institute Inc.) considering pen as experimental unit. Low energy diets reduced final BW (574.6 vs. 571.3 kg; P = 0.03) and ADG (1.517 vs. 1.491 kg/d; P = 0.03) while increased dry matter intake during the finishing phase (12.09 vs. 10.76 kg/d; P< 0.0001). This finding was reflected in lower feed efficiency of LE diets compared to NE diets (0.137 vs. 0.125; P< 0.0001) throughout the entire feedlot period. In addition, as expected, hot carcass weight (P < 0.0001), carcass feed conversion (P < 0.0001), and dressing percentage (P < 0.0001) were compromised in LE diets compared to NE diets. In conclusion, reducing the energy provided by starch feedstuffs, as seen in this study by replacing high-moisture corn with sugar cane bagasse, citrus pulp, and soybean hulls, should be approached carefully, as it may lead to decreased performance and feed efficiency. However, it depends on the input costs and market conditions of each operation.