Dry Matter Intake

What is Dry Matter Intake?

Dry Matter Intake (DMI) is the weight of feed consumed after all water has been removed. It is the most important nutritional metric in cattle feeding because all nutrient requirements — energy, protein, minerals, vitamins — are calculated on a dry matter basis.

Feed is typically 70–85% water (forage) or 10–15% water (concentrates). A cow eating 50 lbs of fresh forage at 75% moisture is actually consuming only 12.5 lbs of dry matter. Comparing feeds on an as-fed basis without adjusting for moisture leads to under- or over-feeding.

DMI is expressed as a percentage of body weight (BW). Lactating cows at peak production consume 3.0–3.5% of BW as DMI. Dry cows consume 1.8–2.0%. Feeder cattle consume 2.5–3.0%. Calves consume 3.0–4.0%. A 1,400 lb Holstein at 3.2% DMI consumes 44.8 lbs of dry matter per day.

Factors affecting DMI include milk yield (higher production = higher intake), forage quality (higher quality = higher intake), fiber content (higher NDF = lower intake), heat stress (reduces DMI 10–35%), feed particle size, and feed bunk management.

Accurate DMI measurement is essential for formulating balanced rations, calculating feed costs per cow, and determining Income Over Feed Cost (IOFC).

How to Estimate DMI on Your Farm

The simplest method uses the standard percentages: weigh the cow, multiply by the appropriate DMI factor. For a 1,400 lb lactating Holstein at peak production: 1,400 × 0.032 = 44.8 lbs DMI/day. For a 1,200 lb Jersey at peak: 1,200 × 0.04 = 48 lbs DMI/day (Jerseys eat more per lb BW due to higher component production). For dry cows: 1,400 × 0.018 = 25.2 lbs DMI/day. These are estimates — actual DMI varies with forage quality, ration palatability, and environmental conditions. The most accurate method is to weigh all feed offered and refused daily, then calculate total consumption.

Heat Stress and DMI

Heat stress is the single biggest reducer of DMI in lactating cows. For every 1°C (1.8°F) increase in temperature-humidity index (THI) above 68, DMI drops approximately 0.4 kg (0.9 lbs) per day. At THI 80 (severe heat stress), a cow eating 50 lbs DMI/day may drop to 35–40 lbs — a 20–30% reduction. This explains why milk production drops 10–35% during summer heat waves even when ration formulation hasn't changed. Management strategies include: fans and sprinklers (reduce effective temperature by 5–10°F), feeding during cooler parts of the day (early morning, evening), increasing ration energy density (more concentrate, less forage), and adding buffers (sodium bicarbonate 0.75–1% of ration DM) to maintain rumen function.

DMI and Feed Cost Accuracy

Feed cost per cow = total ration cost per ton × (DMI in lbs ÷ 2,000). A cow eating 48 lbs DMI/day from a $350/ton TMR costs $8.40/day. But if actual DMI is 44 lbs (not 48), the real cost is $7.70/day — a $0.70/cow/day difference. Over a 305-day lactation, this 4-lb DMI discrepancy means either over-formulating (wasting $213/cow/year) or under-formulating (losing milk production). Regular forage testing, accurate weighing of feed offered and refused, and DMI monitoring through feed bunk management are essential for precise ration economics.