Oorsig/Review Trace Mineral Nutrition of Beef Cattle Application of Injectable Trace Minerals John Arthington Professor and Center Director, University of Florida Cattle have a specific nutritional requirement for trace minerals. These elements are known to support physiological functions related to growth, reproduction, and immunity. For grazing cattle, forage is the primary source of trace minerals with secondary sources being water and ingested soil. In almost all cases, these sources will not fully supply the requirements of grazing cattle, resulting in a deficiency in one or more trace minerals. Trace mineral antagonists, such as sulphur, molybdenum, and iron can further complicate deficiencies. Understanding the specific deficiency and devising a management plan for successful supplementation is the key to optimizing trace mineral nutrition and thus overall cattle performance. Supplementation of trace minerals may occur through a variety of means, including free- choice loose-mineral mixes, trace mineral- fortified blocks, and fortified energy/protein supplements. The most common delivery method for supplemental trace minerals to grazing beef cows is through a free-choice salt lick. Cattle have a nutritional need for sodium and chlorine. This requirement has been realized for centuries due to a natural craving for common salt. In fact, salt is the only nutrient that cattle display a nutritional wisdom for consumption. When supplemental salt is available, sodium deficiency will not occur. This nutritional wisdom does not apply for essential trace minerals, therefore, beef producers often utilize salt as a carrier to deliver other supplemental trace minerals to grazing cattle. The major problem with this management technique is the normal, and sometimes dramatic, seasonal fluctuations in intake of salt-based supplements (Arthington and Swenson, 2004). These fluctuations are due to changes in salt- craving by grazing cattle, often due to increased dry matter of forages and in some cases, increased sodium content of drinking water. Injectable trace minerals (ITM) is another method of supplementation. Injectable trace minerals have been available for many years, but the technology, targeted application, and scientific assessment of efficacy has more recently been a subject of attention among cattle producers, veterinarians, and researchers. An 4 advantage of ITM, compared with traditional oral supplementation methods, is the targeted delivery of a known amount of trace minerals to individual animals. This removes the variability associated with annual fluctuations in voluntary intake of free-choice salt-based supplements. In addition, ITM can be used within production environments that might experience difficulty managing the routine delivery of free-choice mineral mixes, such as extensive rangeland systems, seasonal grazing of mountain meadows, and seasonally flooded pastures. Further, the contribution of wildlife to the overall consumption and disappearance of free-choice mineral mixes can cause complications and add further value to the use of ITM. Our interest in ITM investigation originated from research findings of colleagues at other Universities which reported increased mineral status (Pogge et al., 2012) with increased feed efficiency (Clark et al., 2006), reduced treatments for illness (Berry et al., 2000), and reduced morbidity treatment costs (Richeson et al., 2009) in stressed feeder calves. Our specific research aim was to assess measures of mineral status, performance, and immune competence in beef calves receiving ITM. Collectively, our findings suggest that the trace mineral status of cattle can be increased by the administration of ITM. Additionally, antibody production to vaccine appears to be heightened in calves receiving injectable trace minerals. These responses appear to be evident even in calves exhibiting adequate trace mineral status. It is unclear, therefore, if these observed increases in antibody titers are a response to increased trace mineral status or a priming response to the immune system. Nonetheless, this heightened immune response may be an important contributing factor to the improved measures of health and performance reported by other investigators in previous studies. Prof Arthington will be one of the speakers at the upcoming 2019 Congress of the Ruminant Veterinary Association of South Africa (20 - 22 May, Coastlands Hotel, Umhlanga). Three presentations will be offered that focus on the effective use of ITM in grazing beef cattle production systems.