EFFECT OF RESTRICTED FORAGE INTAKE IN CONFINEMENT ON ESTIMATED FECAL OUTPUT FROM A SUSTAINED-RELEASE BOLUS

Two experiments were conducted to investigate the effects of restricte d forage intake on patterns of chromium excretion to determine sample window duration and the accuracy and precision of fecal output estimat es derived from the Captec Chrome sustained release bolus. In Experim ent 1, 8 crossbred steers (xBAR 243 +/- 14 kg) were assigned randomly to receive prairie hay (PH) at intake levels of either 1.12% body weig ht (BWT) or 0.75% BWT while maintained in individual metabolism crates and(or) pens. In Experiment 2, steers from Experiment 1 were rerandom ized and assigned to receive PH at either 1.12% BWT or alfalfa hay (AH ) at 1.30% BWT. The average post-dosing bolus failure rate across expe riments exceeded 30%. Estimated fecal output exceeded actual fecal out put under all experimental conditions (P < 0.08). Averaged across expe riments, fecal chromium recovery was low (xBAR 55 +/- 4%). When estima ted fecal output was corrected for mean marker recovery within treatme nt, it did not differ from actual fecal output (P > 0.60). Treatment e ffects were similar for estimated fecal output, corrected estimated fe cal output, and actual fecal output. Under conditions of pen feeding a nd restricted forage intake, estimated fecal output exhibited treatmen t differences similar to those of total fecal collection. However, unl ess adjusted for average marker recovery, these estimates were signifi cantly greater than actual fecal output.