Cattle Stocking Rate (AUM)
Available forage (production x area x utilization), animal-unit-months of carrying capacity, head supported.
Example
You enter
- Pasture area (acres) 160
- Forage production (lb/acre) 1500
- Utilization (%) 40
- Animal class cow_calf
- Herd size (optional) 30
You get
- Available forage 96000
- AUMs / carrying capacity 121.52
- Grazing days for the herd 123.08
Checked against published worked examples from: USDA NRCS.
Details, formula, and sources
ScopeAvailable forage (production x area x utilization), animal-unit-months of carrying capacity, head supported, and grazing days for a herd, by animal class. Per the USDA NRCS National Range and Pasture Handbook Ch. 6.
Formula or tableAvailable forage = production (lb/acre) x area (acres) x utilization. AUMs = available forage / 790 lb (one animal-unit-month). Head supported for one AUM (30.4 days) = AUMs / AU-equivalent. Grazing days for a herd = available forage / (herd x AU-equivalent x 26 lb/day).
Source and editionUSDA NRCS National Range and Pasture Handbook Chapter 6 (stocking rate) by name.
Free accessFree at nrcs.usda.gov for the handbook.
What governsEstimate. AHJ and licensed professional govern.
API field namesarea_acres, forage_lb_per_acre, utilization_pct, animal_class, herd_size, available_forage_lb, aums_available, grazing_days
- AUM dry matter 790 lb (26 lb/day x 30.4 days)NRCS National Range and Pasture Handbook
- Animal-unit equivalents cow-calf 1.0, yearling 0.6, 2-year-old 0.8, bull 1.35, sheep 0.2, horse 1.25NRCS NRPH Table 6-5
- Utilization guideline 25-50% arid range, 50-70% tame pasture (take-half-leave-half)NRCS range management practice