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Gestation and Feed Intake Effects on Rate of Passage of Chromic Oxide in Beef Heifers

U. S. Department of Agriculture

Abstract

Rate of passage of Cr₂O₃ was studied with five groups of four pregnant Angus heifers at an average of 150 and 220 days gestation. The groups of heifers were fed mixed and pelleted rations at 60, 80, 100 and 150% of the recommended levels.

Excretion curves at the two stages of gestation did not differ when the Cr₂O³ was expressed as the cumulative percent of the total excreted during the 96-hr, fecal collections. However, when Cr₂O³ was expressed as the cumulative percent of total administered, the recovery was less for the heifers when at 220 days of gestation.

Rate of Cr₂O₃ excretion was more rapid for heifers fed at the 150% level than at lower levels. Rate of passage at the 60, 80 and 100% levels was apparently confounded by the practice of coprophagy by the heifers in the 80% and one of the 60% groups.

Rate of passage expressed as the slope of the diminishing portion of the log of the Cr₂O₃ concentration in the feces did not differ with stage of gestation or level of feed intake.

¹ The authors gratefully acknowledge the assistance of R. R. Oltjen, L. K. Autry and B. Phillips during sample collections.

² A R.S. Animal Husbandry Research Division, Beltsville, Md.

³ A.R.S., Biometrical Services, Beltsville, Md.