Controlled release chromic oxide and alkaline peroxide lignin marker methods

Two digestion trials, using 20 ram lambs (Experiment 1) and 8 cows (Experiment 2) provided ad libitum access to mature prairie grass hay, were conducted to evaluate controlled release intraruminal chromic oxide boluses and alkaline hydrogen peroxide lignin as markers for estimating forage intake by the fecal output/indigestibility ratio. A soybean meal and 3 urea based supplements were fed to lambs in Experiment 1. For both experiments, daily fecal output was weighed and sampled for 6 days (Experiment 1) and 5 days (Experiment 2) beginning 7 days after oral administration of controlled release boluses. Rectal fecal grab samples were also collected at 1000 daily and at 4-hour intervals on day 4 of collections for Experiment 2. For both experiments Cr2O3 excretion rates based on total collections were used to evaluate Cr2O3 controlled release boluses and alkaline hydrogen peroxide lignin predictive value in place of manufacturer's stated release rate. In experiment 1, fecal Cr2O3 output was 224 mg/day +/- 3.9 compared to the manufacturer's stated release rate of 201 mg Cr2O3/day. Fecal alkaline hydrogen peroxide lignin recovery was 97.8% +/- 1.9. Samples composited over the 6-day collection period predicted fecal output, apparent dry matter digestibility, and dry matter intake similar (P = .44, .15 and .55; respectively) to actual values. Supplemental treatment and dry matter intake had no effect (P > .38) on daily fecal Cr2O3 output or alkaline hydrogen peroxide lignin recovery. In Experiment 2, fecal Cr2O3 was 1,662 mg/day +/- 63 compared to the manufacturer's stated release rate of 1,505 mg Cr2O3/day. Fecal alkaline hydrogen peroxide lignin recovery was 95.9% +/- 7. Using 5-day composited samples, predicted fecal output, dry matter digestibility, and dry matter intake were similar (P = .49, .21 and .49; respectively) to actual values. Increasing the number of daily grab samples increased R2 values between actual and predicted fecal output and dry matter digestibility. Fecal grab samples and total fecal collection samples provided a similar relationship (R2=.71) between actual and predicted dry matter intake when each were composited over 5 days. Time of day did not affect fecal Cr2O3 or alkaline hydrogen peroxide lignin concentrations. These results suggest that grab samples collected once daily on 5 consecutive days can be used to predict fecal output when Cr2O3 controlled release boluses are used. Although recoveries of fecal alkaline hydrogen peroxide lignin were near 100% in these experiments, digestibility estimates using this internal marker were variable and adversely influenced predictions of dry matter intake.