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Research-Article| Volume 72, ISSUE 3, P708-714, March 1989

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Comparison of Two Models Used to Estimate In Situ Nitrogen Disappearance1

  • Author Footnotes
    2 To whom requests for reprints should be addressed.
    S.C. Denham
    Footnotes
    2 To whom requests for reprints should be addressed.
    Affiliations
    Animal Science Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611
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  • Author Footnotes
    3 Present address: Purina de Venezuela, Ave. Principal de los Ruices, Edif. Stemo, 4to Piso, Caracas, Venezuela.
    G.A. Morantes
    Footnotes
    3 Present address: Purina de Venezuela, Ave. Principal de los Ruices, Edif. Stemo, 4to Piso, Caracas, Venezuela.
    Affiliations
    Animal Science Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611
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  • D.B. Bates
    Affiliations
    Animal Science Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611
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  • J.E. Moore
    Affiliations
    Animal Science Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611
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  • Author Footnotes
    1 Florida Agricultural Experiment Station Journal Series No. 9139.
    2 To whom requests for reprints should be addressed.
    3 Present address: Purina de Venezuela, Ave. Principal de los Ruices, Edif. Stemo, 4to Piso, Caracas, Venezuela.
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      Abstract

      Inclusion of lag time into a model describing in situ N disappearance influenced the parameter estimates describing N degradability and improved the goodness-of-fit of the model to data describing aeschynomene hay and alfalfa meal digestion. Ruminal N disappearance (%) was described using two models that assumed: 1) digestion of the potentially digestible but insoluble N fraction was initiated immediately upon exposure to ruminal contents, or 2) digestion of this fraction was preceded by a lag period during which hydration and microbial attachment is presumed to occur prior to the initiation of digestion. Digestion was assumed to occur from a homogeneous potentially digestible but insoluble N fraction by a first order process described by a rate constant, k. Incorporating a lag term resulted in an increase in the rapidly soluble N fraction, a decrease in the potentially digestible but insoluble N fraction, and a decrease in the total digestible N fraction. The two forages had different k values when fit to the nonlagged model but not when fit to the lagged model. The residual standard deviation was smaller for the lagged model, and the fit of predicted values to observed values was improved.

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