134. Characterization of Daily Feeder Attendance and Blood Urea Nitrogen Dynamics in Mature Beef Cows Grazing Native Range

Abstract The objective of this study was to characterize the feeding behavior of mature beef cows grazing native range using a 4-wheel lick tank equipped with an automated tag reader system. Twenty mature Angus and Angus-cross cows were observed over a 25-d period during September–October, following a 28-d adaptation period. Cows were managed in a 31.4-ha pasture at the Range Cow Research Center, North Range Unit, Oklahoma State University. Each cow was equipped with an ultra-high-frequency (UHF) RFID tag, and the lick tank was fitted with a HerdView Tag Reader (HerdX Inc., Dallas, TX) to record start and end times of each feeder visit. Events lasting < 10 s were excluded. Data were summarized across the 25-d period and partitioned by hour, day, and individual cow. Mean feeder visit duration was 5.08 ± 3.80 min (range 0.17–32.5 min), while the mean of the daily total time spent at the feeder per cow was 32.1 ± 10.5 min (range 12.5–47.9 min). Hourly summaries revealed distinct daily patterns, with the highest number of visits at 2000 h (mean duration 4.27 ± 3.13 min) and the lowest at 1200 h (5.52 ± 3.05 min). A large proportion of feeder activity occurred between 1700 and 2300 h (53.54% of observations), while midday hours (1100–1500 h) accounted for 4.57%. On average, cows visited the feeder during 4.47 ± 1.16 different hours each day, indicating feeding activity was distributed across multiple periods. Blood urea nitrogen (BUN) was measured on day 22. BUN concentration was positively correlated with the number of feeder visits (r = 0.69) and average daily time spent at the feeder (r = 0.61) over the 25-d period, indicating that cows with greater cumulative feeder attendance exhibited higher BUN concentrations. A post hoc power analysis using herd mean and SD (32.1 ± 10.5 min ) for mean total time spent at the feeder per cow per day indicated that sample sizes required to detect differences of 1, 2, 3, 4, 5, or 10 min per day (power = 0.8, α = 0.05) were 1,699, 426, 190, 108, 69, and 16 cows per group or treatment, respectively. The results from this study suggest that daily feeder attendance was consistent, although the total time spent at the feeder was variable from day to day. A strong correlation between standardized BUN and feeder visits suggests that data recorded by the HerdView Tag Reader reflects liquid supplement intake.