Effect of restricted forage intake in confinement on estimated fecal output from a sustained release bolus.

Abstract

Two experiments were conducted to investigate the effects of restricted forage intake on patterns of chromium excretion to determine sample window duration and the accuracy and precision of fecal output estimates derived from the Captec Chrome sustained release bolus. In Experiment 1, 8 crossbred steers (mean = 243 +/- 14 kg) were assigned randomly to receive prairie hay (PH) at intake levels of either 1.12% body weight (BWT) or 0.75% BWT while maintained in individual metabolism crates and(or) pens. In Experiment 2, steers from Experiment 1 were rerandomized 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 experiments exceeded 30%. Estimated fecal output exceeded actual fecal output under all experimental conditions (P<0.08). Averaged across experiments, fecal chromium recovery was low (mean = 55 +/- 4%). When estimated fecal output was corrected for mean marker recovery within treatment, it did not differ from actual fecal output (P>0.60). Treatment effects were similar for estimated fecal output, corrected estimated fecal output, and actual fecal output. Under conditions of pen feeding and restricted forage intake, estimated fecal output exhibited treatment differences similar to those of total fecal collection. However, unless adjusted for average marker recovery, these estimates were significantly greater than actual fecal output.