Animals for the season
4head
- 9.03.6acres eachha each
- 32AUMs
- 25%eaten
- The animals eat about 25% of what grows. The rest is trampled, soiled or left to regrow.
- That is 32 animal-unit months of grazing.
- It feeds about 4 animals (cow with calf, 1,200 lb) for 6 months. Each counts as 1.2 animal units.
- That is about 9 acres for each one.
How we work it out
- Forage eaten = acres × forage an acre × the share eaten (25%, or 30% to 35% when you move them).
- Animal-unit months (AUMs) = forage eaten ÷ 780 lb.
- Head = AUMs ÷ (animal units each × months).
The method and the 780 lb are SDSU's. Animal units are the USDA NRCS table, as printed by Arizona. SDSU's example: 2,500 lb an acre × 0.25 = 625 lb, ÷ 780 = about 0.8 AUM an acre.
Animal units
| Animal | Animal units |
|---|---|
| Cow with calf, 1,000 lb | 1 |
| Cow with calf, 1,200 lb | 1.2 |
| Cow with calf, 1,400 lb | 1.4 |
| Cow with calf, 1,600 lb | 1.6 |
| Dry cow, 1,000 lb | 0.92 |
| Bull | 1.35 |
| Cattle, 1 year old | 0.6 |
| Cattle, 2 years old | 0.8 |
| Horse | 1.25 |
| Sheep | 0.2 |
| Lamb, 1 year old | 0.15 |
| Goat | 0.15 |
| Goat kid, 1 year old | 0.1 |
USDA NRCS. SDSU gives some animals more: a horse 1.50, a goat 0.17, a bull 1.30.
Land they will not use
Steep ground and ground far from water get grazed less. SDSU cuts the stocking rate on that part of the pasture:
- Slope of 15% to 30%: cut 30%. 31% to 60%: cut 60%. Over 60%: do not count it.
- 1 to 2 miles from water: cut 50%. 2 to 3 miles: cut 75%.
Questions
How many acres per cow?
It depends on how much your pasture grows. At 2,500 lb of forage an acre, grazed all season, a 1,200 lb cow and calf need about 1.5 acres a month. For 6 months, about 9 acres.
What is an animal unit?
A 1,000 lb cow with her calf. She eats about 26 lb of dry forage a day. Other animals count as a share of her: a horse is 1.25, a sheep 0.2, a goat 0.15.
What is an AUM?
An animal-unit month: the forage one animal unit eats in a month. SDSU uses 780 lb of dry forage. Arizona uses about 800 lb, and NDSU 913 lb of air-dried forage.
Why do the animals eat only 25%?
If you take half and leave half, about 25% gets eaten. Another 25% is trampled, soiled or dies back, says SDSU. Moving animals between pastures lets them eat 30% to 35%.
How do I know how much my pasture grows?
Clip the grass inside a hoop, dry it and weigh it. With SDSU's 4.8 sq ft hoop, grams × 20 gives pounds an acre.
Sources
- SDSU Extension S-0013-51, Setting the Stocking Rate2020The method, 780 lb of forage an animal-unit month, harvest efficiency, the worked example
- University of Arizona, Stocking Small Pastures Using AUMs (USDA NRCS table)2010Animal-unit equivalents, from the NRCS National Range and Pasture Handbook
- NDSU Extension R1810, Determining Carrying Capacity and Stocking RatesApr 2024A second worked example, with air-dried forage