Use of New Technologies to Evaluate the Environmental Footprint of Feedlot Systems

Livestock production systems can have appreciable effects on the environment; especially concentrated animal feeding operations (CAFO) where large numbers of animals and the nutrients they consume and excrete are concentrated. The major environmental issues of feedlots are gaseous emissions of ammonia, odors, and greenhouse gases, nutrient losses in manure, and nutrient losses in runoff, if runoff control systems are improperly managed. Gas concentrations can be measured using techniques ranging from simple adsorbents to gas chromatography to open-path-lasers and FTIR. Use of absorbents is less expensive, but more labor intensive. In addition laser technologies can provide concentrations in real time. Gaseous emissions can be measured using several micrometeorological techniques. The backward Lagrangian stochastic (bLS) model is the most commonly used because of its simplicity; however, the equipment can be expensive. Micro-met methods are generally limited to use in large areas (> 1 square km), and are not appropriate for small research feedlots. Small (< 1 square m) static, or flow-through chambers maybe used to measure gaseous emissions from pen surfaces. These are adequate for comparing treatments, but chambers with air exchange rates of less than 15/min usually underestimate true flux rates; especially for gases such as ammonia. Newer “static-type” chambers that measure gas concentrations continuously may accurately measure emissions because of their short sampling time. The SF6 method and the GreenFeed system (C-Lock, Inc., Rapid City, SD) are frequently used to measure enteric methane emissions from individual animals. The GreenFeed requires less labor, but has a higher initial cost. Large “respiration type” chambers that house groups of animals, are used to measure emissions from simulated pens. These have the advantage of measuring both animal and manure emissions; however, they may have limitations in measuring some emissions because of their low air exchange rates. Capture of bioaerosols, and use of molecular techniques are also gaining in acceptance. Sampling systems commonly used to capture bioaerosols include impaction, impingement, and high-volume. Culture-independent techniques are also gaining in acceptance for the identification and quantification of microorganisms in the gut, manure, and air. Losses of nutrients from entire research pens and commercial feedyards have been estimated using natural internal digestion markers and the change in the N/P or N/ash ratio between diets and pen manure. Unfortunately, many air quality studies that use new technologies frequently forget to use long-established technologies, such as adequate nutrient analysis of animal diets and measurements of nutrient intake.