284 Nutrient density on arrival and phase-feeding effects on economic returns of feedlot cattle.

Abstract The feedlot industry is an evolving system that continues to innovate and adapt based on market supply and demand. In recent years, the shift in favor of carcass-based marketing has led to increased days on feed in an effort to increase hot carcass weight, improve quality grade distribution, and realize greater economic returns. In addition, consolidation of cow herds, rising environmental pressures, and an increase in the proportion of beef × dairy crossbreds on feed has stimulated cattle feeders to explore placement of lighter weight cattle, further increasing days on feed and subsequently the risk for morbidity and mortality from respiratory and metabolic health challenges. In these scenarios, the diet and management strategies used during both the receiving period and immediately before harvest may be critically important to maximize health, performance, and profitability. During the marketing process cattle are exposed to a series of stressors and novel pathogens which can induce immunosuppression and increase susceptibility to bovine respiratory disease. After arrival, cattle are exposed to additional stressors such as processing and provision of novel feedstuffs, and typically exhibit low DMI for the first 7 to 14 d of the receiving period. Most feedlots supply newly received cattle with a diet containing a high proportion of roughage, which is paradoxical, as these animals are likely in a negative energy balance from lack of feed and water during transport and marketing, low DMI following arrival, and increased nutrient requirements to support immune and inflammatory processes. To offset these challenges, researchers have explored feeding high concentrate diets at arrival to increase dietary energy intake. Both protein concentration and degradability in receiving diets also warrant further investigation. Modifying the timing and duration of the transition from the receiving to the finishing diet and use of program or limit-feeding regimens are also alternative management strategies that can be used to influence performance and growth composition of lighter weight cattle. In addition to the receiving period, the end of the finishing period immediately before harvest represents a crucial time where mortalities are most economically impactful, feed efficiency declines, and management strategies such as terminal sorting and use of beta-adrenergic agonists may influence consumption patterns and composition of gain. Modifying the fiber concentration during the later portion of the finishing period and protein concentration during beta-agonist administration have been explored to improve digestive health, performance, and carcass outcomes. Therefore, the objective of the current symposia is to summarize the performance, health, and economic implications of dietary nutrient density and targeted management strategies that can be used at both arrival and the end of the finishing period in feedlot cattle.