Estimating carrying capacity of a pasture
There is no standard reference on the available forage amount for different pastures in the intermountain west. Dryland pastures in most Colorado counties typically range from 300-2000 pounds per acre in total usable dry matter. Irrigated pastures range from 2,000-6,000 pounds per acre. Typically, dryland in most counties produces 1,000 pounds, decreasing as you go toward more arid environments in the west. Thus, a typical dryland pasture has around 500 pounds of usable forage (dry matter basis, foraging only 50% as previously mentioned) per acre. To know for sure, clip a small area of mature grass representative of the pasture, and weigh it after allowing it to air dry for three or four days. For example, if you clip 100 sf, multiply the pounds by 435.6 to get pounds per acre.
- Grazing animals need 2-3% of their body weight of air-dried forage daily. Thus, a 1000-pound cow needs approximately 25 pounds of air-dried forage a day or 750 pounds of dry forage per month. Therefore, a 1000 pound cow needs 1.5 (or almost 2) acres per month.
- Horses are the same, but they tend to waste and trample more forage, and 3-4% of their body weight per day is more typical.
- Sheep need 2-3% of their body weight; however, they utilize a higher percentage of brush species and forbs than cattle or horses.
- Llamas tend to have slightly more efficient digestive systems and require only 1.8-2% of their body weight of air-dried forage daily.
- To estimate the total carrying capacity of a pasture take the estimated air-dried forage production divided by 2 times the number of acres:
Estimated Air-Dried Forage Production/2 x Number of Acres = Total Carrying Capacity
This is the total available production of the pasture that will sustain the existing desirable vegetation.
Then calculate the needed forage to sustain all the animals for a day. Next, divide forage availability by forage need to discover the amount of days the pasture can sustain grazing during the growing season. Or you can save yourself from all of this and call the Agriculture Agent at the Extension Office or your local NRCS office who will do it for you.
Tips for Improving Small Pastures:
- Brush removal: Rabbit brush and sage brush are examples of native bushes that can increase in a pasture and limit forage production.
- A combination of herbicide and brush hogging (heavy duty rotary mower) is the best strategy for lasting removal of sage brush. Brush hogging alone will remove all existing material, but the brush grows back after 2-3 years. By brush hogging first and then treating the new growth with an herbicide, there is a much greater success rate (80-100% removal). This also allows for a lower herbicide dose as the plant is already stressed from the brush hogging. Check with the local Division of Parks and Wildlife to prevent destruction of important wildlife habitat.
- Encourage more grass:
- Be sure grazing is not so severe that it reduces grass density. If so, reduce the grazing intensity or allow for longer rest periods.
- Keep animals off the pasture in the spring until grasses are four to six inches tall.
- Divide your pasture into grazing cells and use a rotating grazing scheme. Rotational grazing uses the “take half and leave half” principle and lets you manage your pasture more intensively. This can lead to more forage production and greater carrying capacity and overall healthier pastures. Seek additional advice from the Extension or NRCS Office for help implement a rotational grazing plan.
- Control your weeds. Pastures that have been overgrazed will have more broadleaf plants, weeds, and shrub species than grasses. Applying a broadleaf herbicide suppresses weed species and aids the grass’ re-establishment. Prior to herbicide application, carefully read the label and adhere to the rate recommendation, personal protective equipment, and grazing restrictions. Be particularly careful in spraying poisonous plants as many herbicides change the sugar composition of poisonous plants, making once unpalatable plants, more palatable and more likely to poison livestock and horses.
- In worst case scenarios, where a pasture is severely overgrazed or weedy, reseeding may be necessary. Reseed with a mixture of grass species adapted to your conditions and goals to have a better chance at establishment.
- Fertilize only as needed: The best method to determine the fertilizer needs of your pasture is by doing a soil test. Hay pastures will need more nitrogen to replace the vegetation removed even if you use it onsite and spread the manure. Pastures that are only grazed will need fewer nutrients. Over-application of nutrients tends to favor invasive weeds over perennial grasses.
Creating a sacrifice area
Any grazing management system must include a sacrifice or dry lot area. Livestock must be kept in the sacrifice area when the pasture is not ready for grazing. The sacrifice area should be located in a dry area protected from floods and where the runoff from the dry lot does not contaminate a well, stream or other water body. The sacrifice area should allow sufficient square feet per animal based on the species.
- Dairy cattle – 600 sq. ft.
- Beef cattle – 500 sq. ft.
- Horse – 400 to 500 sq. ft.
- Goat, sheep – 25 sq. ft.