On a farm of under forty hectares, every division of land carries weight. Paddock sizing is the starting point for any rotational grazing system, and getting the numbers roughly right before putting posts in the ground saves significant labour and forage loss later. The goal is to size each paddock so that a group of livestock can graze it down to the target residual height in three to five days, then move on.
The Animal Unit as a Planning Tool
Forage demand is standardized through the animal unit (AU) concept. A standard AU represents a mature beef cow of approximately 454 kg consuming around 12 kg of dry matter per day. All other livestock classes are expressed as fractions or multiples of this baseline. A ewe with lambs typically falls between 0.2 and 0.25 AU, while a stocker steer of 275 kg lands around 0.6 AU.
Calculating total AU for a farm gives a consistent denominator. A mixed operation running 20 beef cows (1.0 AU each) and 60 ewes with lambs (0.22 AU each) carries 20 + 13.2 = 33.2 AU. That number drives the rest of the paddock calculation.
Forage Availability Estimates
Forage availability varies by region, soil type, and species mix, but temperate Canadian pastures in reasonable condition can carry between 1,500 and 2,500 kg of dry matter per hectare at the time of grazing. Using a conservative figure of 1,800 kg per hectare and a utilization rate of 60 to 70 percent (the remainder left as residual to protect root reserves), available forage per hectare comes to roughly 1,100 to 1,260 kg of dry matter.
Working figure: At 1,800 kg DM/ha with 65% utilization, plan on approximately 1,170 kg of harvestable dry matter per hectare per grazing event.
Calculating Paddock Area
With AU count, daily dry matter requirement, and forage availability established, paddock area follows from a straightforward calculation:
| Variable | Example Value |
|---|---|
| Total animal units | 33.2 AU |
| Daily DM intake per AU | 12 kg DM/day |
| Grazing days per paddock | 4 days |
| Total DM needed per paddock | 33.2 × 12 × 4 = 1,594 kg |
| Harvestable DM per hectare | 1,170 kg/ha |
| Paddock area required | 1,594 ÷ 1,170 = ~1.36 ha |
For a 30-day rest period, a system needs at least 30 ÷ 4 + 1 = 8 to 9 paddocks. On a 20-hectare grazeable area, that works out to roughly 2.0 to 2.5 ha per paddock — above the 1.36 ha calculated. The difference is useful buffer, accounting for variable forage growth and dry periods.
Paddock Shape and Fencing Considerations
Square or nearly square paddocks minimize fencing material for a given area. Long, narrow paddocks increase the perimeter-to-area ratio, raising material and labour costs. On rolling terrain, paddock boundaries often follow natural features: waterways, ridgelines, or existing hedgerows. These can be incorporated into the design to reduce fencing runs.
Temporary electric fencing using polywire or polytape on step-in posts offers flexibility for farms still experimenting with paddock numbers and sizes. Many small-farm operators in Ontario and British Columbia start with permanent perimeter fencing and use temporary subdivision to dial in the rotation before committing to permanent internal posts.
Water Access
Each paddock requires dependable water access. Livestock unwilling to walk more than 250 metres to water show lower forage intake and more concentrated grazing near water points. On farms where a central water line is not feasible, portable tanks moved with each paddock shift are a practical alternative, though they add daily management time.
Adjusting for Mixed-Species Systems
Farms running sheep and cattle together face slightly different paddock sizing logic. Cattle and sheep graze at different heights — cattle work well at 15 to 25 cm entry height, while sheep are effective grazers down to 5 to 8 cm. Sequential grazing, where cattle graze first and sheep follow a day or two later cleaning up the shorter growth, can increase total forage utilization per paddock without overgrazing individual plants.
When calculating paddock size for mixed systems, sum the AU for all species and apply the same formula. Adjust the utilization target upward slightly (to 70 to 75%) if sequential grazing is used, since the additional pass by sheep captures forage that cattle leave.
Reviewing and Revising Paddock Sizes
Paddock sizes calculated on paper are starting estimates. In practice, forage production varies year to year with rainfall, temperature, and management history. Reviewing residual height after each grazing event — using a simple pasture ruler or rising plate meter — gives direct feedback on whether paddocks are sized correctly. If livestock are consistently cleaning paddocks to below the target residual in under three days, paddocks may be too small or stocking density too high for current forage conditions.
References
- Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). Grazing Management. ontario.ca/page/managed-grazing
- Agriculture and Agri-Food Canada. Forage and Grazing Resources. agr.gc.ca
- Voisin, A. (1959). Grass Productivity. Island Press. (Public domain foundational text.)