SUPPLEMENT AND FORAGE EFFECTS ON FECAL OUTPUT ESTIMATES FROM AN INTRARUMINAL MARKER DEVICE

Three experiments were conducted to evaluate effects of supplemental p rotein and forage on marker estimated fecal output using an intrarumin al continuous release marker device in grazing steers. In experiment 1 , twelve steers were assigned to 3 treatments and fecal collections we re made during a 6-day period in December 1990 and again in February 1 991. Treatments were: 1) range forage only, 2) range forage + 0.32 kg protein/day from a 70% soybean meal - 30% wheat pellet, and 3) range f orage + 0.32 kg crude protein/day from 15.1% meadow hay. Fecal output estimates derived from the marker device were similar (P > 0.10) for a ll treatments and both periods. Fecal estimates derived from the marke r device were greater (P < 0.01) than fecal output from total fecal co llection (3.5 kg/day vs 2.7 kg/day); the correlation between estimates from fecal collection and the marker device was 0.85. In experiment 2 , ten steers were assigned to treatments 1 and 2 of experiment 1 durin g December 1991. Fecal output derived from the marker device was simil ar (P > 0.10) for the 2 supplement treatments. Fecal output estimates were greater (P < 0.10) for the marker device than fecal collection (1 .80 kg/day vs 11.63 kg/day); the correlation between estimates from th e marker device and total collection was 0.94. In experiment 3, fecal output was derived from the marker device during three 5-day collectio n periods. Steers grazed upland range in July (green immature forage) and September (cured mature forage) and grazed subirrigated meadow (im mature regrowth) in October. Fecal output estimates from the marker de vice were different (P < 0.,05) between collection periods, (e.g., for age sources). When compared to total fecal collection, the marker devi ce underestimated fecal output on range in July (P < 0.01, 2.1 kg/day vs 2.5 kg/day) and on meadow in October (P < 0.01, 2.6 kg/day vs 3.5 k g/day). Correlations between the marker device and fecal collection we re 0.93 in July and 0.99 in October, respectively. Estimates from the marker device and total fecal collection were similar (P > 0.10; r = 0 .93) on range in September. Protein supplements had no effect on fecal estimates derived from chromic oxide released from a marker device, b ut the marker estimates were affected by forage source. Correlation be tween fecal collection and the marker method is high; however, total f ecal collection should be used to correct fecal output derived by the marker device for each forage source.