BEEF SPECIES SYMPOSIUM: An assessment of the 1996 Beef NRC: Metabolizable protein supply and demand and effectiveness of model performance prediction of beef females within extensive grazing systems1,2,3

Abstract

Interannual variation of forage quantity and quality driven by precipitation events influence beef livestock production systems within the Southern and Northern Plains and Pacific West, which combined represent 60% (approximately 17.5 million) of the total beef cows in the United States. The beef cattle requirements published by the NRC are an important tool and excellent resource for both professionals and producers to use when implementing feeding practices and nutritional programs within the various production systems. The objectives of this paper include evaluation of the 1996 Beef NRC model in terms of effectiveness in predicting extensive range beef cow performance within arid and semiarid environments using available data sets, identifying model inefficiencies that could be refined to improve the precision of predicting protein supply and demand for range beef cows, and last, providing recommendations for future areas of research. An important addition to the current Beef NRC model would be to allow users to provide region-specific forage characteristics and the ability to describe supplement composition, amount, and delivery frequency. Beef NRC models would then need to be modified to account for the N recycling that occurs throughout a supplementation interval and the impact that this would have on microbial efficiency and microbial protein supply. The Beef NRC should also consider the role of ruminal and postruminal supply and demand of specific limiting AA. Additional considerations should include the partitioning effects of nitrogenous compounds under different physiological production stages (e.g., lactation, pregnancy, and periods of BW loss). The intent of information provided is to aid revision of the Beef NRC by providing supporting material for changes and identifying gaps in existing scientific literature where future research is needed to enhance the predictive precision and application of the Beef NRC models.

A Comparative Analysis of the Nutrient Composition and Digestibility of California Perennial and Annual Grasses at Four Stages of Growth

“…These lands are populated by several annual and perennial species of grasses and forbs. Waterman et al (2014) argued in favor of the need for regionally specific nutrient composition data of forages, in accordance with seasonal dynamics. This information may provide ranchers and land managers with greater knowledge to aid management decisions for the maintenance and increased performance of their animals (Murray et al, 1978) in addition to enhancing rangeland health.…”

“…Minimal information is known about the nutritional composition of California rangeland perennial and annual grass species at various stages of growth (phenologies; Ganskopp and Bohnert, 2001), and more specifically, their relative digestibilities as they relate to grazing beef cattle (Waterman et al, 2014). Further understanding of nutritional value and digestibility of common California plants may provide ranchers and land managers with the knowledge to make management decisions for the maintenance and increased performance of their animals (Murray et al, 1978).…”

“…There is minimal information published about the quantity and quality of California rangeland perennial and annual grasses and forbs in regards to seasonal and environmental variation at various stages of growth (phenologies; Ganskopp and Bohnert, 2001;Waterman et al, 2014). Further understanding of the seasonal nutritional value and digestibility of common California grasses and forbs may provide ranchers and land managers with the knowledge to make management decisions for the maintenance and increased performance of their animals.…”

“…Knowledge of environmental factors is imperative from a range livestock standpoint because forage nutrient supply curves are highly dependent upon climate (Waterman et al, 2014). The patterns of change in nutritional quality (increases in fiber content and decreases in crude protein, water, and digestibility) upon maturity are similar from year to year because phenological development is regulated primarily by photoperiod.…”

“…Both perennial and annual growth types can be C3 or C4 plants (National Forage and Grasslands Curriculum, 2016). Air and soil temperatures affect whether a C3 or C4 will occur in a given region or not (Waterman et al, 2014). The optimum air temperature range for the growth of C3 plants is 65-75 o F and, for C4 plants, 90-95 o F. The optimum soil temperature range for C3 plants is 40-45 o F, and for C4 plants, 60-65 o F. As the temperature increases, C3 plants lose efficiency, whereas C4 plants become more efficient.…”