Dairy Cow Dry Matter Intake Calculator
Predicted dry matter intake for a lactating dairy cow from body weight, milk yield, milk fat and days in milk (NRC 2001), converted to as-fed forage and concentrate amounts, water needs and feed cost per litre of milk.
How it works
DMI (kg/d) = (0.372 × FCM + 0.0968 × BW^0.75) × (1 − e^(−0.192 × (weeks in milk + 3.67))) (NRC 2001); FCM = 0.4 × milk + 15 × fat (kg); as-fed = DM ÷ DM%
How much a dairy cow can eat sets the ceiling on how much she can milk without mining her body reserves, so predicting dry matter intake is the starting point of every ration. The NRC 2001 equation builds it from milk energy demand (fat-corrected milk), maintenance (metabolic body weight) and a lag term for early lactation, when intake climbs more slowly than milk yield and the cow runs an energy deficit. A high-producing Holstein eats 3.5–4% of her body weight in dry matter; converting that to the wet weight of silage and concentrate actually put in the bunk is where most on-farm mistakes happen, because silage dry matter swings from 28% to 45%. The forage-to-concentrate split then determines rumen health and cost: more concentrate raises energy density and cost per day but lowers cost per litre only up to a point.
Worked example
A 650 kg cow at 32 kg of 3.8% milk and 90 days in milk: FCM 31.0 kg, predicted DMI 23.0 kg (3.5% of body weight). At 55% forage in a 38% DM silage that is 33 kg of silage plus 11.8 kg of concentrate as fed — about $5.60 a day, or 17.5¢ per kg of milk, with roughly 65 litres of water.
Frequently asked questions
Why is actual intake lower than predicted?
Heat stress, poor forage quality or fermentation, limited bunk space, lameness, sorting and empty bunks all cut intake; a 10% shortfall costs 2–3 kg of milk.
What about dry cows and heifers?
Dry cows eat about 1.8–2.2% of body weight (less in the close-up period); growing heifers 2.5–3%. This equation is for lactating cows only.
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Farm planning estimate. Breeds, climate, feed quality and local extension guidance change the numbers — use this to plan, and your own records to manage.