Short communication: Comparison of 3 solid digesta passage markers in dairy cows.
This study investigated the usefulness of acid-detergent fiber-bound (15)N [acid detergent insoluble (ADI)-(15)N] as a solid digesta passage marker in dairy cows compared with chromium (Cr) and ytterbium (Yb) (as labeled fiber or forage, respectively). Intrinsically (ADI-(15)N) or extrinsically (Cr, Yb) labeled alfalfa hay was pulse-dosed intraruminally to 7 lactating dairy cows. Following marker administration, spot fecal samples were collected for up to 72 h for marker analyses. Urine and milk samples were also collected and analyzed for Yb and Cr. Fecal marker excretion data were processed using 2-compartment mathematical age-dependent/age-independent (Gn→G1) models. The rate of passage of the marker in the first, age-dependent compartment tended to be slower for Yb compared with Cr and ADI-(15)N, which resulted in a trend for longer mean retention time (MRT) in this compartment when Yb was used as a marker (19.0 h) compared with Cr and ADI-(15)N (14.5 and 13.9h, respectively). The rate constant of marker disappearance for the second or age-independent compartment tended to be greater for Yb compared with Cr and ADI-(15)N, which led to a shorter MRT of Yb in this compartment (15.6) versus ADI-(15)N (32.1) and Cr (24.8h). The cumulative MRT was greater for ADI-(15)N versus Cr and Yb (46.0, 39.3, and 34.4h, respectively). Total MRT of marker tended to be greater for ADI-(15)N than for Yb (46.6 vs. 36.6h, respectively). Urine and milk analyses data suggested no measurable losses of Yb along the digestive tract, but about 0.79% of Cr dosed intraruminally was secreted or excreted in milk and urine in the 48-h period following marker administration. Collectively, this study confirmed previous observations that ADI-(15)N can be used reliably as a solid digesta passage marker for ruminants, producing pre-duodenal and total-tract retention times similar to that of Cr-labeled fiber. Retention time in the age-independent compartment was underestimated when Yb was used as a marker, emphasizing the need to process forages to isolate fiber before labeling with Yb.
Department of Animal Science, Pennsylvania State University, University Park 16802.
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Lee
Department of Animal Science, Pennsylvania State University, University Park 16802. Electronic address: anh13@psu.edu.
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Hristov
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D015415:Biomarkers / Q000032:analysis; D002417:Cattle / Q000502:physiology*; D002857:Chromium / Q000032:analysis*; D003612:Dairying / Q000379:methods*; D004032:Diet / Q000662:veterinary; D004063:Digestion; D005260:Female; D005766:Gastrointestinal Contents / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D012820:Silage / Q000032:analysis; D015018:Ytterbium / Q000032:analysis*
D015415:Biomarkers; D009587:Nitrogen Isotopes; D002857:Chromium; D015018:Ytterbium; D009584:Nitrogen
chromium; dairy cow; nitrogen-15; passage rate marker; ytterbium