Calculating Dry Matter Intake

UpdatedSeptember 9, 2025

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How to Calculate Dry Matter Intake (DMI) from Pasture for Organic Dairy Operations

Summary: Calculating Dry Matter Intake (DMI) from pasture is essential for organic dairy farms to meet USDA National Organic Program (NOP) requirements. Lactating dairy cows must get at least 30% of their DMI from pasture during the grazing season.

This article explains how to gather records, calculate pasture intake for different animal groups, and handle changing rations using weighted averages to ensure organic compliance and improve grazing management.

Why Calculate DMI from Pasture?

Organic dairy certification requires that lactating animals receive at least 30% of their dry matter intake from pasture during the grazing season. Calculating DMI from pasture:

Ensures compliance with organic standards
Supports sustainable and effective grazing management
Helps prepare accurate records for inspections and audits
Improves herd nutrition planning

Step 1: Gather Your Records and Tools

Before calculating DMI from pasture, collect these key documents:

Organic System Plan (OSP):
- L3R Section: Lists rations and dry matter demands by animal group
- L6 Section: Details grazing season start and end dates
Grazing Calendar: Tracks actual days animals spent on pasture
As-Fed Feed Records: Amounts and types of supplemental feeds given daily
Dry Matter Reference Charts: Moisture content (%) for each feed type
Dry Matter Intake Worksheets: Blank sheets or Excel templates for calculations

Step 2: Identify Animal Groups and Their Feed Demands

Divide your herd into production classes because each group has unique nutritional needs and grazing access. Typical groups include:

Unbred Heifers
Bred Heifers
Dry Cows
Milking Cows

Use the OSP (L3R) to find each group’s daily dry matter demand (in pounds).

Step 3: Calculate Daily DMI from Pasture for Each Group

For each group, follow this method:

Determine total daily dry matter demand (e.g., 20 lbs/day).
Calculate dry matter from supplemental feed:
Convert as-fed amounts to dry matter using reference charts (e.g., 17 lbs haylage @ 65% DM = 11.05 lbs dry matter).
Estimate pasture intake:
Subtract supplemental feed DM from total demand.
Calculate pasture percentage:
Divide pasture intake by total demand, then multiply by 100.

Example: Bred Heifers

Demand: 20 lbs dry matter/day
Supplemental feed: 17 lbs haylage @ 65% DM = 11.05 lbs DM
Pasture intake = 20 – 11.05 = 8.95 lbs
Pasture DMI % = (8.95 ÷ 20) × 100 = 44.75%

Step 4: Calculate Weighted Average DMI for Groups with Changing Rations

For groups like milking cows that receive different rations over the grazing season:

Calculate pasture DMI % for each ration period.
Multiply each percentage by the number of days on that ration.
Sum these values.
Divide by the total grazing days to get the weighted average pasture DMI %.

Example: Milking Cows Over 234-Day Grazing Season

Ration Period	Pasture DMI %	Days	Weighted Value (DMI % × Days)
3/25–7/1	51.95%	98	5,091
7/2–8/1	64.59%	30	1,938
8/2–11/16	43.79%	106	4,642
Totals		234	11,671

Weighted average = 11,671 ÷ 234 = 49.87% DMI from pasture

This is well above the 30% NOP minimum requirement.

Additional Tips and Considerations

Keep detailed, accurate records: Consistent documentation supports audit readiness and certification maintenance.
Adjust calculations for regional grazing seasons: Grazing dates may vary by region; document any deviations clearly in your OSP.
Use spreadsheets for accuracy: Excel or similar tools simplify weighted average calculations and record management.
Consult regional experts: Oregon Tilth can provide guidance specific to your climate and pasture conditions.