Grazing Capacity Calculator – Animal Units

One animal unit (AU) is a 454 kg cow with calf, eating about 390 kg of forage dry matter per month (26 kg DM/day, ~2.6% of bodyweight). The “take half, leave half” rule caps harvest at 50% of standing forage — the rest protects root reserves and regrowth. Worked example: a 40 ha pasture producing 3,000 kg DM/ha per season with 50% usable forage: usable = 40 × 3,000 × 0.5 = 60,000 kg ÷ 390 = 154 AUMs — 154 cow-months, i.e. 38 cows for 4 months or 19 for 8 months. Sheep count as 0.2 AU (a 70 kg ewe eats about 2.6 kg DM/day). Rotational paddocks lift utilization toward 55–60% versus 40–45% continuous.

1. 1

   Step 1

   Enter pasture area and forage production (kg DM/ha — clip or estimate).

2. 2

   Step 2

   Set utilization: 50% standard, 40% on fragile range.

3. 3

   Step 3

   Enter herd as animal-unit equivalents.

4. 4

   Step 4

   Read grazing months, paddock days and stocking rate AU/ha.

• 1

  One AU = 454 kg cow ≈ 390 kg DM/month

• 2

  Leave 10–12 cm residual on improved pastures

• 3

  Drought plan: destock 30% early, not late

• 4

  Measure forage with a grazing stick or clipping frames

• Stocking to a wet year’s forage and crashing in the dry one

• Counting 100% of forage as eatable — 50% utilization is the ceiling

• Ignoring lactation: a milking cow eats 20–30% more DM

• No residual monitoring — bare paddocks stop regrowing