Galyean Appreciation Club review: knowledge gaps in the nutrition of grazing beef cattle.

Feeding the increasing world population is a grand challenge for animal agriculture. Ruminants in general, and beef cattle specifically, fill a unique role in addressing this challenge as they convert large quantities of forage-based feed resources, which are inedible by humans, into high-quality, nutrient food products for human consumption. In North American beef cattle production systems, grazed forage represents a large portion of whole-herd dietary intake. In fact, within the United States, approximately 57% of the feed energy required to produce 1 kg of beef carcass weight is derived from grazing systems, and another 19% of feed energy is provided by harvested forage sources. Nutritional management of grazing beef herds is a critical component of efficient and effective production systems. Understanding nutrient supply and demand fosters more precise approaches to strategic supplementation practices. Limited source data from grazing beef cattle constrain modeling approaches of nutrient supply and demand and consequently limit our ability to nutritionally manage grazing beef cattle. Reviewing the available data exposes numerous knowledge gaps in the nutrition of grazing beef cattle. Needs include more robust source data collection and data collection technologies in the specific areas of intake, macro and micronutrient supply and demand, and nutrient demands associated with environmental extremes and physical activity. Additionally, more accurate and precise mathematical models are needed in the area of intake, energy, protein, and micronutrient supply and demand. In addition, coupling investigations of grazing livestock nutrition with behavior, climate, land use, socioeconomic, and sustainability needs will foster a more holistic understanding of the importance of accurately assessing and managing grazing cattle nutrition. Extensive opportunities exist to improve grazing livestock nutrition and consequently enhance sustainable capture of grazed forage nutrients and improved beef cattle production from grazing lands; however, limited funding streams to support these research efforts limit progress.