Revised digestive parameter estimates for the Molly cow model
- 1 June 2013
- journal article
- Published by American Dairy Science Association in Journal of Dairy Science
- Vol. 96 (6), 3867-3885
- https://doi.org/10.3168/jds.2012-6183
Abstract
The Molly cow model represents nutrient digestion and metabolism based on a mechanistic representation of the key biological elements. Digestive parameters were derived ad hoc from literature observations or were assumed. Preliminary work determined that several of these parameters did not represent the true relationships. The current work was undertaken to derive ruminal and postruminal digestive parameters and to use a meta-approach to assess the effects of interactions among nutrients and identify areas of model weakness. Model predictions were compared with a database of literature observations containing 233 treatment means. Mean square prediction errors were assessed to characterize model performance. Ruminal pH prediction equations had substantial mean bias, which caused problems in fiber digestion and microbial growth predictions. The pH prediction equation was reparameterized simultaneously with the several ruminal and postruminal digestion parameters, resulting in more realistic parameter estimates for ruminal fiber digestion, and moderate reductions in prediction errors for pH, neutral detergent fiber, acid detergent fiber, and microbial N outflow from the rumen; and postruminal digestion of neutral detergent fiber, acid detergent fiber, and protein. Prediction errors are still large for ruminal ammonia and outflow of starch from the rumen. The gain in microbial efficiency associated with fat feeding was found to be more than twice the original estimate, but in contrast to prior assumptions, fat feeding did not exert negative effects on fiber and protein degradation in the rumen. Microbial responses to ruminal ammonia concentrations were half saturated at 0.2mM versus the original estimate of 1.2mM. Residuals analyses indicated that additional progress could be made in predicting microbial N outflow, volatile fatty acid production and concentrations, and cycling of N between blood and the rumen. These additional corrections should lead to an even more robust representation of the effects of dietary nutrients on ruminal metabolism and nutrient absorption, of animal performance, and the environmental impact of dairy production.Keywords
Funding Information
- Virginia State Dairymen’s Association
- New Zealand Dairy Farmers through DairyNZ Ltd.
This publication has 96 references indexed in Scilit:
- Estimating greenhouse gas emissions from New Zealand dairy systems using a mechanistic whole farm model and inventory methodologyAnimal Feed Science and Technology, 2011
- In situ dry matter, crude protein, and starch degradabilities of selected grains and by-product feedsAnimal Feed Science and Technology, 1998
- Causes of Inacurate Prediction of Volatile Fatty Acids by Simulation Models of Rumen Function in Lactating CowsJournal of Theoretical Biology, 1997
- Impact of Nonfiber Carbohydrate on Intake, Digestion, and Milk Production by Dairy CowsJournal of Dairy Science, 1994
- Nonstructural Carbohydrate and Protein Effects on Rumen Fermentation, Nutrient Flow, and Performance of Dairy CowsJournal of Dairy Science, 1993
- Modeling of Rumen Water Kinetics and Effects of Rumen pH ChangesJournal of Dairy Science, 1988
- Metabolism of the lactating cow: II. Digestive elements of a mechanistic modelJournal of Dairy Research, 1987
- Metabolism of the lactating cow: III. Properties of mechanistic models suitable for evaluation of energetic relationships and factors involved in the partition of nutrientsJournal of Dairy Research, 1987
- Metabolism of the lactating cow: I. Animal elements of a mechanistic modelJournal of Dairy Research, 1987
- Ruminal Degradation of Dried Brewers Grains, Wet Brewers Grains, and Soybean MealJournal of Dairy Science, 1986