Grazing
Stocking rate calculator: cows per acre
Balance what the pasture grows against what the cows eat, before the grass tells you the hard way.
Stocking rate = forage the cattle can use ÷ forage each cow needs. Usable forage is acres × pounds of forage grown per acre × the share the cattle actually eat. A cow needs about 2.6% of her body weight in dry forage per day. On 640 acres growing 2,000 lb per acre at 25% harvest, 1,200 lb cows grazing all year need about 11,400 lb each, so the pasture carries about 28 cows, or 23 acres per cow.
Example numbers. Change them to your own.
Choosing the inputs
- Forage grown per year. Use your own clipping data or the production figure for your soil and site from the USDA NRCS Web Soil Survey. It changes a lot from a wet year to a dry one.
- Share the cattle eat. On rangeland, 25% is the usual planning figure: half the growth is left standing, and of the half that is removed, about half is lost to trampling, insects and wildlife. Well-managed rotational grazing on improved pasture can reach 35% or more.
- Cow weight. One animal unit is a 1,000 lb cow eating about 26 lb of dry forage a day. Heavier cows eat more, so use your real cow weight.
- Adjust every year. Stock for the forage you have, not the average year. Recheck after the growing season.
How many acres does a cow need?
It depends on how much forage the land grows. Divide the forage one cow needs for the grazing period by the usable forage per acre. Improved pasture in a high-rainfall area can carry a cow on 2 acres or less, while dry rangeland can take 30 acres or more.
What is an animal unit?
One animal unit (AU) is a 1,000 lb cow, with or without a calf under about six months, eating roughly 26 lb of dry forage per day. An animal unit month (AUM) is the forage one animal unit eats in a month, about 780 lb.
What does take half, leave half mean?
It is the rangeland rule that no more than half of the year’s forage growth should be removed, so plants keep enough leaf to regrow. Because part of what is removed is trampled or eaten by wildlife, cattle end up eating about a quarter of the total.