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Variability in in situ ruminal degradation parameters causes imprecision in estimated ruminal digestibility
T J Hackmann1, J D Sampson, J N Spain
1Division of Animal Sciences, University of Missouri, Columbia 65211, USA.
Journal of Dairy Science
|February 23, 2010
Summary
Variation in ruminal degradation parameters significantly impacts forage digestibility estimates. Using mean values can lead to imprecise results, questioning their practical significance in animal nutrition.
Area of Science:
- Animal Science
- Nutritional Biochemistry
- Ruminant Nutrition
Background:
- Ruminal digestibility is key for feed evaluation.
- Degradation parameters (rate, extent) are commonly used for estimation.
- Existing data suggest significant variation in these parameters.
Purpose of the Study:
- Quantify degradation parameter variation in forage hays.
- Assess the impact of this variation on ruminal digestibility estimates.
Main Methods:
- Utilized previously published degradation data for alfalfa, grass, and grass-legume hays.
- Estimated ruminal digestibilities of various chemical fractions.
- Calculated 95% confidence limits using propagation of uncertainty.
Main Results:
- High coefficients of variation were observed for degradation parameters (e.g., 24.8% for rate, 28.6% for instant fraction).
- Confidence limits for digestibility were substantial, often overlapping even with distinct means.
- Uncertainty in degradation rate alone caused significant imprecision in digestibility estimates.
Conclusions:
- Mean degradation parameters may yield imprecise and biologically insignificant digestibility values.
- The inherent variation in degradation parameters, particularly rate, necessitates caution when estimating forage digestibility.
- Rethinking the reliance on mean degradation parameters for feed evaluation is advised.
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