Monitoring Diet Quality and Projecting Body Condition Score in Cattle Using Fecal Near Infrared Spectroscopy and NUTBAL on a Southern Arizona Rangeland

Range cattle grazing in semi-arid regions are commonly limited by lack of nutrients from low-quality forage. Due to this, ranchers are faced with the challenge of monitoring diet quality in order to address nutrient limitations. Near infrared spectroscopy (NIRS) of fecal samples is a method used to determine diet quality values like crude protein (CP) and digestible organic matter (DOM) in grazing animals. When combined with a nutritional balance analyzer such as the NUTBAL system, fecal NIRS can be used to monitor diet quality and project animal performance. Our research aimed to test the ability of NUTBAL to project animal performance as represented by body condition score (BCS) in cattle (n=82 Animal Units) grazing on the Santa Rita Experimental Range (SRER) in southern Arizona. Previous work conducted on other Arizona rangelands led to the hypothesis that fecal NIRS coupled with NUTBAL can be used to monitor diet quality and project BCS in a southern Arizona commercial grazing operation. Data collection occurred between June 2016 and June 2017. Standing biomass and botanical composition were measured before each grazing period, and relative utilization was measured following each grazing period. During the midpoint of grazing in each pasture, 30 body condition scores and a fecal composite of 15 samples were collected. Fecal derived diet quality varied between a maximum of 10.75% CP and 61.25% DOM in early August 2016, to a minimum value of 4.00 % CP and 58.40 % DOM in March 2017. This study confirmed the ability of fecal NIRS paired with NUTBAL to project future BCS within 0.5 a score point more than 80% of the time in cattle grazing on the SRER. With this information, cattle managers in southern Arizona can better address animal performance needs and nutrient deficiencies