Effect of high-sugar grasses on methane emissions simulated using a dynamic model

Area of Science:

• Agricultural Science
• Environmental Science
• Animal Nutrition

Background:

• High-sugar grasses are explored for reducing nitrogen (N) excretion in cattle.
• Feeding high-sugar grasses alters rumen fermentation, potentially impacting methane (CH4) emissions.
• Limited in vivo data exists on the effect of high-sugar grasses on CH4 emissions.

Purpose of the Study:

• To evaluate the effect of high-sugar grasses on simulated CH4 emissions in dairy cattle using a modeling approach.
• To assess how dietary changes associated with high-sugar grasses influence CH4 production.

Main Methods:

• Utilized an existing dynamic, mechanistic model of enteric fermentation and intestinal digestion.
• Constructed a simulation database to analyze model behavior under various conditions.
• Simulated effects of increased water-soluble carbohydrate (WSC) levels, changes in crude protein (CP) and neutral detergent fiber (NDF), N fertilization, and grain feeding.

Main Results:

• Simulated CH4 emissions generally increased with higher WSC content when expressed as MJ/day or % of gross energy intake.
• CH4 emissions (g/kg milk) showed variable results, sometimes decreasing due to increased milk yield.
• Largest CH4 increases occurred when WSC replaced CP; effects were less pronounced when replacing NDF.

Conclusions:

• High-sugar grass strategies to mitigate N excretion may inadvertently increase CH4 emissions.
• The outcome depends on grass composition, dry matter intake (DMI), and the units used to express CH4.
• Modeling is a valuable tool for hypothesis testing in animal nutrition and environmental impact studies.