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Range cattle grazing in arid and semi-arid regions are commonly limited by lack of nutrients from low-quality forage. Due to this, managers are faced with the challenge of monitoring diet quality in order to address nutrient limitations. Near-infrared spectroscopy of fecal samples (fNIRS) is a method used to determine diet quality in grazing animals. When combined with a nutritional balance analyzer such as the NUTBAL system, fNIRS can be used to monitor nutritional status and predict animal performance. In addition, previous research has shown that forage intake and forage quality are positively correlated. Our research aims to test the ability of NUTBAL to predict animal performance as represented by body condition score in cattle grazing on the Santa Rita Experimental Range in southern Arizona. This research also aims to determine the relationship between available forage and diet quality. Beginning in June of 2016, body condition score and fecal samples were collected from the Santa Rita Ranch�s registered Red Angus herd (n=82 AU). During the midpoint of the grazing period in each pasture, 30 body condition scores and a fecal composite of 15 samples were collected. Additional opportune samples are gathered during periods of expected nutrient stress. Vegetation sampling includes estimates of standing biomass and botanical composition before the herd enters a pasture. After the herd exits each pasture, herbaceous utilization is measured and browse use is determined. Diet crude protein was 6.01%, 4.31%, and 5.86% on June 10, June 24, and July 13 respectively. We hypothesize that cattle diet quality is positively correlated to available forage and that body condition score can be accurately predicted through the use of fNIRS coupled with NUTBAL. With this information, cattle managers in southern Arizona can better address nutrient deficiencies of grazing animals.