NUTRITIONAL AND MANAGEMENT STRATEGIES TO IMPROVE PERFORMANCE, NUTRIENT DIGESTIBILITY, AND SUSTAINABILITY OF FEEDLOT CATTLE

A series of studies were conducted to evaluate live animal performance, health, carcass characteristics, nutrient digestibility, ruminal characteristics, and environmental emissions of feedlot cattle. The first study explored the impacts of feeding an industry standard finishing diet throughout the receiving and finishing period compared to a high roughage receiving diet during the receiving period with subsequent adaptation to the finishing diet on health, performance, serum chemistry, ruminal pH, and rumination of high-risk feedlot cattle. Treatment diets were offered ad libitum and consisted of: 1) finishing diet for the entire feeding period (FIN) or 2) receiving diet for the first 56 d, followed by transition to the finishing diet (REC). All cattle were consuming the same diet on d 74. A subset of cattle were randomly selected to quantify ruminal pH, temperature, and rumination time. Ultrasound images were captured on d 0, 74, and 146 to determine fat thickness, and carcass characteristics were determined after slaughter. Cattle fed REC had greater (P < 0.01) dry matter intake (DMI) from d 0 to 74, but DMI did not differ (P = 0.80) from d 74 to the end of the finishing period (final). Metabolizable energy intake was not different from d 0 to 74 (P = 0.20), d 74 to final (P = 0.80), or overall (P = 0.78). At d 74 and final, body weight (BW) of FIN was 10 kg greater (P ≤ 0.10) than REC. Cattle consuming FIN had greater (P < 0.01) average daily gain (ADG) and increased (P < 0.01) gain:feed (G:F) from d 0 to 74. Feed cost of gain (FCOG) was less for FIN from d 0 to 74 (P < 0.01), but not different from d 74 to final (P = 0.89). There was no difference (P ≥ 0.31) in health outcomes between treatments. On d 74, FIN had greater (P = 0.04) fat thickness over the rump and rib, but did not differ (P ≥ 0.41) at d 146 or in the carcass. Carcasses of FIN had greater (P = 0.04) hot carcass weight (HCW), but no difference (P ≥ 0.12) in ribeye area, yield grade, or quality grade. There was no difference (P = 0.18) in liver abscess rate between treatments. Ruminal pH was greater (diet × day interaction; P < 0.01) for FIN on d 2 and 61, and rumination time was less (diet × day interaction P < 0.01) for FIN from d 0 to 28. Because of increased G:F and decreased FCOG with no impact on health, providing a finishing diet to high-risk calves upon arrival may be a viable alternative to a traditional receiving diet. The second study evaluated effects of feeding grain milling products (GMP) on nutrient digestion, passage rate, ruminal pH, and ruminal volatile fatty acid (VFA) and ammonia concentrations of ruminally fistulated beef cattle. Four Angus × Hereford steers were used in a 4 × 4 Latin square design. Each period consisted of 21 d of dietary adaptation, 5 d of total tract digestibility and passage rate, volatile fatty acid (VFA) and ammonia (NH3), and ruminal pH collections, 3 d of in situ rumen digestibility, and 1 d for rumen evacuations. Diets were analyzed for physically effective neutral detergent fiber (peNDF) using the Penn State Particle Separator. Treatments were no GMP (CON), 20% wet distillers grains with solubles (WDGS20), 20% Sweet Bran (SB20), or a combination of 10% wet distillers grains with solubles and 20% Sweet Bran (COMBO). The proportion of dietary particles > 4.0 mm was greatest (P < 0.01) for CON, intermediate for SB20, and least for WDGS20 and COMBO, but peNDF did not differ (P = 0.11) among treatments. Total tract neutral detergent fiber (NDF) digestibility was greater (P ≤ 0.05) for COMBO than CON, and acid detergent fiber (ADF) digestibility was greater for WDGS20, SB20, and COMBO than CON. A diet × hour interaction (P ≤ 0.05) was observed for molar proportions of propionate, butyrate, and valerate. Ruminal pH also had a diet × hour interaction (P = 0.02). There was a tendency (P = 0.07) for area under the curve (AUC) of 5.6 to be greater for SB20 and COMBO compared to CON. Before rumen evacuations, there was a tendency for DMI to be greater (P = 0.06) for GMP diets than cattle consuming CON. Although there was no difference (P = 0.26) in the DM quantity of rumen particulate, CON had the greatest (P = 0.01) amount of particulate relative to DM intake. Rumen evacuated samples from WDGS20 had a greater (P ≤ 0.05) quantity of crude protein, NDF, ADF, and ether extract compared to SB20. Overall, inclusion of GMP in the diet improved total tract fiber digestion, altered VFA concentrations and nutrients within the rumen particulate, and tended to increase AUC. In the final study, a model was developed to depict and compare feedlot diets and growth technologies used in 1990 vs. 2020 and their influence on cattle performance and carbon footprint was determined. Dietary changes from 1990 to 2020 included the adoption of GMP feeds while decreasing inclusion of corn and traditional roughage sources. In 1990, available growth technologies included estradiol implants and the ionophore monensin; whereas, in 2020 combination implants including both trenbolone acetate and estradiol, monensin, and ractopamine hydrochloride (in the final 28 to 42 d) were used. In both 1990 and 2020, use of available technologies increased final BW, ADG, G:F, and HCW compared to no technology. From 1990 to 2020 initial BW, final BW, ADG, G:F, and HCW, and DMI increased. Total days on feed (DOF) increased by 44 in 2020 compared to 1990. Use of growth technologies in both 1990 and 2020 decreased total greenhouse gas emissions per animal (CO2e). Because cattle had greater DOF in 2020 than 1990, all sources of greenhouse gas emissions per animal increased. However, because of greater total BW gain in 2020, when expressed as CO2e/kg BW gain, greenhouse gas emissions decreased by 4.4% from 1990 to 2020. Feedlots in 2020 produced 47.5% more BW gain with 1.4% less cattle, while only increasing total CO2e by 39.5%, indicating changes in technologies and diet formulations have improved efficiency and reduced the carbon footprint of feedlot cattle production in the past 30 yr.