Stocking Rate Calculator

How the Stocking Rate Calculator works

Stocking rate calculator: grass grown against grass eaten

"How many sheep per acre?" has no single answer. It depends on how much grass the land grows, how much of that grass the animals actually eat, how big the animals are and how long they are out. This calculator makes each of those an input, so you can see the effect of improving pasture, extending the season or switching species instead of relying on a rule of thumb that was true for someone else's farm.

Why it matters. Overstocking is the most common and most expensive grazing mistake. Grass grazed below about 4 cm recovers slowly, weeds and bare patches move in, and the field grows less next year, so the carrying capacity falls just as you need it. Animals lose condition and worm burdens rise, and buying in forage in a dry summer costs far more than the stock were worth. Understocking wastes land: grass that is not eaten goes to seed, loses feed value and has to be topped. Stocking limits also carry legal weight. Agri-environment agreements, tenancy clauses and nitrate rules cap stocking in livestock units per hectare, and horse livery yards are regularly asked how many animals a paddock can take.

Grass growth. Pasture yield is measured in kilograms of dry matter (DM) per hectare per year. Rough hill grazing may grow 2,000 kg DM/ha and unimproved permanent pasture around 4,000. Average lowland grass grows about 6,000, fertilised improved pasture 8,000–10,000, and a well-managed perennial ryegrass ley with nitrogen can exceed 12,000. A plate meter or sward stick gives a measured figure. Without one, pick the description in the table below that matches your land, and be conservative.

Utilisation. Animals never eat everything that grows. Set stocking with continuous grazing uses about 50–60 %. Rotational or paddock grazing reaches 70–80 %, because each paddock is grazed hard and then rested. The rest is trampled, fouled, rejected or dies back. Sixty percent is a fair default for an ordinary set-stocked field.

Intake. The calculator assumes each animal eats 2.5 % of its bodyweight in dry matter a day, a sensible average for stock at grass. A 600 kg cow needs 15 kg DM a day and a 70 kg ewe 1.75 kg. Lactating and growing animals eat towards 3 %, dry stock nearer 2 %, so adjust the weight field if your animals are heavier or lighter than the typical figure.

The stocking rate formula

Usable grass = growth × utilisation × area. Head carried = usable grass ÷ (daily intake × grazing days). The livestock unit figure uses a 650 kg cow as 1 LU, so different species can be compared on one scale.

Worked example. Take 10 ha of average pasture at 6,000 kg DM/ha and 60 % utilisation, grazed for 180 days. That gives 36,000 kg of usable grass. A 600 kg cow eats 15 kg a day, or 2,700 kg over the season, so the field carries 36,000 ÷ 2,700 = 13.3 cows, about 1.3 per hectare. The same field would carry about 114 ewes at 70 kg each, since each ewe eats 315 kg over the season.

A second example: how many horses per acre? A 500 kg horse eats 12.5 kg DM a day. On a 2-acre paddock of 6,000 kg grass at 50 % utilisation (horses graze selectively and leave latrine areas), used year-round for 365 days, usable grass is 2,428 kg against 4,563 kg eaten, so the result is about 0.53 horses. In practice that means one horse on two acres needs hay through the winter, which matches the usual advice of 1–1.5 acres per horse plus supplementary feed.

The table under the result shows how many head this area carries at each pasture quality, using your animal, utilisation and number of days.

How to read the result.

• Animals the area can carry is the headline number of head for the grazing period. Round down, never up.
• Stocking rate gives the same figure per hectare and per acre, for comparing fields of different sizes.
• Livestock units gives the total LU and LU/ha. This is the figure agri-environment schemes and tenancy agreements quote. Many extensive grassland options cap it at somewhere between 0.5 and 1.4 LU/ha, so check your own agreement.
• Usable grass shows the season's edible dry matter, so you can see how much a change in utilisation is worth.
• Each animal eats gives the daily and seasonal intake in dry matter.
• Area per animal inverts the stocking rate. It is the easiest figure to explain to a buyer or a livery client.

Tips and pitfalls.

• Growth is not spread evenly through the year. In the UK about 60 % arrives between April and June, so a field that carries 13 cows over the season may carry 20 in May and 6 in August. Plan to take a silage or hay cut in spring, or buy in stock then.
• Dry years can cut growth by a third. Test your plan at 4,000 kg as well as 6,000.
• Mixed grazing helps. Sheep and cattle eat different parts of the sward, and running them together or one after the other raises utilisation.
• Poaching on wet soils destroys more grass than the animals eat. Heavy clay should come off early in autumn regardless of what the numbers say.

These figures cover the grazing season only. For the months when grass stops growing, use the feed calculator to budget hay or silage.

Stocking rate by animal

Pasture growth in kg DM per hectare, 60% utilisation over 180 days.

Head per hectare and area per animal by animal and pasture growth

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