Technical note: effectiveness of different methods of continuous marker administration for estimating fecal output.

Six ruminally fistulated crossbred steers (BW = 369 kg) were used in a randomized complete block experiment to test the efficacy of continuous-infusion pumps and controlled-release boluses for administering external markers to predict fecal output. Steers, limit-fed chopped alfalfa hay at 2% of BW daily, were fitted with continuous-infusion pumps that administered Co-EDTA and YbCl3 solutions intraruminally. In addition, a controlled-release bolus containing Cr2O3 was inserted into the rumen of each steer. Fecal grab samples were taken every 6 h for 7 d during initial marker equilibration; after this period, fecal grab samples were taken every 3 h for 48 h to evaluate diurnal variation patterns. Steers were subsequently fitted with fecal bags for 7 d to allow total fecal collection. Grab samples also were taken during the total fecal collection period at 0600 (AM) and 1400 (PM). The marker X time effect was nonsignificant. Similarly, time of grab sampling (AM or PM) did not affect estimates of fecal output (P greater than .10), but the Cr2O3 bolus overestimated fecal output (P less than .05). Fecal marker concentrations during the 48-h profile showed little diurnal variation regardless of marker used. All markers equilibrated in the feces at approximately 100 to 120 h after initiating infusions. The continuous-infusion pumps evaluated were efficacious for administering markers for estimating total fecal output in limit-fed steers; however, the Cr2O3 boluses evaluated overestimated fecal output when the manufacturer's suggested release rate was used for fecal output calculations.