Abstract The in situ mobile bag procedure was used to compare rumen undegradable protein (RUP) content and RUP digestibility of Nebraska Sandhills range and meadow diet samples. Meadow samples (n = 12) were from June, July and August of 2 years while range samples (n = 19) were from June, July, September and December of 6 years. Samples were collected using esophageally fistulated cows (samples from 2 cows composited per time point), freeze-dried, and ground through a 2 mm screen. For each sample, 1.25 g was weighed into 8 replicate 8×10 cm Dacron bags with 50-µm pore size. Rumen incubation time was based on estimated digestibility and passage rate. Following rumen incubation, analysis of neutral detergent insoluble N (NDIN) on one-half of the bags was used to calculate RUP content. Remaining bags were treated with pepsin/HCl solution (37 °C) and stirred for three hours before duodenal incubation. Analysis of NDIN after recovery from feces determined RUP digestibility. Data were analyzed using month as a fixed effect and year and experiment as random effects. In meadow samples, CP (15.0% of DM) was consistent across June, July, and August (P = 0.72). Range samples tended to differ in CP content (P = 0.11), with June, July and September being similar (8.15% of DM) while December was 6.01%. In meadow samples, RUP averaged 21.9% of CP while range samples averaged 26.7% of CP, with no differences due to month (P ≥ 0.32). Because CP content was changing in range samples, RUP as a % of DM tended (P = 0.14) to decrease in December (1.66) compared to June, July, and Sept (2.25). In meadow samples, RUP digestibility (%) declined from 74.7% in June to 61.4% in July and Aug (P = 0.07). RUP digestibility (%) averaged 43.9% for all range samples (P = 0.66).