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Automated Long-Term Total Collection Versus Indicator Method to Estimate Duodenal Digesta Flow in Cattle^1,2,

University of Arizona, Tucson 85721

Abstract

Four steers, fitted with re-entrant duodenal cannulas, were used to compare digesta flow as measured by automated total collection (ATC) with flow estimations based on chromium oxide (Cr₂O₃) and lignin concentrations of representative samples of 24-h collection of digesta. In two successive periods, each steer was fed about 4 kg/d of either an all-forage or an 80% sorghum grain diet. Duodenal digesta samples were automatically taken and pooled every 2 h, during the 3- to 6-d total collections. For animals adapted to the collection procedures, there was no consistent evidence of flow inhibition in the first 24 h of a long-term total collection. Flow rates of duodenal digesta and dry matter (DM), estimated by Cr₂O₃ and lignin were 15% greater and more variable than those measured by ATC. Digesta flow rates measured by ATC averaged 65 liters/d in steers fed the forage diet and 42 liters/d in the same steers receiving the grain diet. Apparent ruminal DM disappearance, calculated from direct measurements by ATC was 44% for the grain diet and 37% for the forage diet. Ruminal DM disappearance, based on Cr₂O₃ and lignin, was about 25% lower than the ATC values. The data indicate that the use of total collection procedures should include replication over days. Duodenal flow rates suggested a 24-h cyclic pattern of digesta flow for the grain diet, with a peak about midnight followed by a period of low flow before the onset of the light hours. Chromium oxide showed a similar flow pattern, but flow rate decreased more rapidly following the midafternoon peak. With the forage diet, 24-h patterns were only observed for Cr₂O₃ and lignin concentrations in duodenal digesta, which appeared different from the Cr₂O₃ concentration pattern with the grain diet. Diurnal variation of digesta flow was greater than day-to-day variation. Because of the diurnal variation, spot-sampling techniques must be considered very carefully, since inadequate sampling could easily misrepresent total collection samples and flow estimates. The data also suggest caution in the use of lignin as a marker in grain diets, and of Cr₂O₃ as a marker in forage diets for partitioning digestion in the duodenum of ruminants.

¹ Arizona Agr. Exp. Sta. Journal Article 3920.

² This paper is part of a dissertation prepared by the senior author in partial fulfillment for the Ph.D. degree in Agr. Biochem. and Nutr.

³ Dept. Anim. Sci.

⁴ Present address: Dept. Anim. Sci., Virginia Polytechnic Institute and State University, Blacksburg, VA.

⁵ Dept. Vet. Sci.

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