70 Evaluation of nutritional monitoring techniques for beef cattle grazing Texas gulf coast rangelands

Abstract Projecting grazing cattle performance based on forage quality is still a challenge for nutritional modeling and monitoring for livestock producers and researchers. Therefore, our objective was to evaluate the effectiveness of fecal near infrared reflectance spectroscopy (FNIRS) in conjunction with the Nutritional Balance Analyzer (Nutbal) system as a grazing cattle nutrition tool. Commercially available FNIRS diet quality calibrations derived from diet chemistry and fecal spectra representing a diverse set of rangeland and forage types across the U.S. have successfully predicted cattle performance in multiple environments, but there have been location specific instances of poor results. This study evaluated diet crude protein (CP) and digestible organic matter (DOM) and subsequent projection of body condition/body weight change of rangeland beef cattle grazing three ranches in the gulf coast region of Texas from October 2022 to October 2023. Cattle used in this study ranged in age from 30 mo - old primiparous heifers to 78 mo - old mature cows maintained under a variety of management practices including different calving season (Spring or Fall), pasture rotation schedules, and supplementation with protein cubes or protein/ energy lick tubs. On each sampling date, a herd composite of 10 to 15 fresh individual fecal pats were collected to represent the pasture where cattle were currently grazing. Body condition scores (BCS) were recorded at each sampling event, every 4 to 6 wk. Projected body weight/BCS was derived from Nutbal. Differences in observed and predicted BCS were determined via paired T-test with significance at P < 0.05. The herd with the greatest agreement (75%) between observed and predicted BCS (P > 0.1), had BCS means of 5.15 ± 0.07 and 5.12 ± 0.14, respectively. In contrast, the herd with the least agreement (36%; P < 0.01) had an observed BCS mean of 5.78 ± 0.10 and a mean FNIRS/Nutbal predicted BCS of 6.28 ±0.14. In conclusion, the FNIRS/Nutbal system as currently applied was able to satisfactorily predict grazing cattle herd performance in some ranches/herds of the gulf coast region. However, further investigation is necessary to address and understand the factors contributing to specific instances of disagreement between observed and predicted BCS. This information will be used to improve the performance of the FNIRS/Nutbal system.