AbstractA study was conducted to compare the effectiveness of administering one bolus of 15 g of chromium oxide (Cr203) at 8 am or 4 pm versus two boluses of 7.5 g each at 8 am and 4 pm. The daily excretion pattern of Cr2O3 was determined to estimate the best time of day to take rectal fecal samples from each animal. Twelve Holstein and Brown Swiss heifers of 282.5 kg mean live weight were used in a complete randomized design. The animals grazed a mixture of improved tropical grass pastures during the entire trial. There were no significant differences among treatments. Neither the number of boluses (one vs. two) nor the time of administration (8 am and/or 4 pm) had a significant effect upon the total mean concentration of Cr2O3 in dry feces (mg/g), collected twice per day (8 am and 4 pm) for seven days. Higher simple correlation coefficients (P < 0.01) were obtained between the total fecal Cr2O3 average concentration on the 4th day and the mean concentration from two fecal samples collected at different hour-combinations. The more reliable morning and afternoon hour combinations for sampling feces were 8 am and 6 pm (r = 0 .94) and 10 am and 6 pm (r = 0.92). Three days was found to be the minimum time required for the stabilization of the Cr2O3 concentration in dry feces.
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