Stocking Rates

How many animals per acre for your pasture are too many? The first step in making this determination is calculating what the grazing animal’s daily forage needs are and then comparing that needed amount to the daily amount of forage produced in the pasture. The end product of this calculation can be referred to as the pasture’s Stocking Rate. The following information provides guidelines for understanding and figuring out Stocking Rates. For specific information on your particular situation, contact your local NRCS or Extension office.

Animal Forage Requirements

Forage consumption is affected by many factors and varies with individual animals. Factors include forage quality, age of animal, topography, breed type and health condition to name a few. The average daily forage intake for most animals is 2.6% of their body weight per day. Remember this figure can vary from 1.5% to 3.5%. For ease, the calculations listed in Table 1 for daily, monthly and yearly forage requirements are based on 2.6% of body weight.

*The above listed numbers reflect forage weight on an oven dried basis, and do not account the amount of forage lost per day due to trampling.

The second part of the stocking rate equation is determining how much forage a pasture can supply.

Average Forage Production

The amount of forage produced per acre will vary significantly from one site to another. These variations are the result of climate, soil, type of forage, available moisture and degree of management. Here on the Front Range of Colorado, it is typical to find forage production levels between 200 to 2,000 pounds annually per acre in dryland pastures. Irrigated pastures will produce from 2,000 to 10,000 per acre. Please refer to the chart below for a listing of typical, Annual Useable Production levels.

*The Annual Useable Yield as listed above is based on the production level of typical rangeland found in the Eastern Front Range of Colorado in fair to good ecological condition under normal annual precipitation.

The amounts listed in the Average Annual Useable Yield column are 50% of the actual estimated forage produced per year. This is in keeping with a rule of thumb called the “take half, leave half” method. It is thought that if only half of a plant’s annual growth is consumed, the remaining one half of the above ground portion of the plant is sufficient to collect sunlight and nutrients to carry it over to the next growing season in a healthy, reproductive state.

Example of Determining Stocking Rates

Table 3 contains an example of determining the Stocking Rate on 10 acres of Dryland Native Pasture on Loamy Soils. One cow & calf, two horses and one sheep are used in this example.

The Example in Table 3 shows that this pasture can support these animals only 36 days out of every year. However, these animals need to eat every day of the year. Now what? Now it’s time to set up your grazing system!

Grazing Systems

Continuing with the example given above let’s work through a couple of optional grazing systems.

Yearlong Grazing

Year long grazing implies that the animals will be left in one pasture all year long. However, in this situation there is not enough forage to sustain those animals all year. So, we must do a few modifications. This pasture should be used only as a “turn-out” area that will supply a small fraction of the total forage needs for these animals. The balance of the feed requirements should be derived from another source such as hay or hay and grain.

So, let’s say that the animals will graze the pasture for 2 hours a day, 365 days per year. How will the animals’ nutritional needs be met? Let’s look at Tables 4 & 5.

Rotational Grazing

There are several types of rotational grazing systems. These systems have certain advantages over yearlong grazing. For this example we will work with a simple two-pasture rotational system. For ease of management, it is better to try and make the pastures equal in size if their production levels are equal.

Using the above example of a 10-acre lot of land, we now split the pasture into two 5-acre pastures with cross fencing. In order to achieve the benefits of rotational grazing, one pasture should be grazed while the other is in a state of rest. Important things happen while a pasture is being rested, including leaf growth, root growth, and plant reproduction. All of these functions are necessary to maintain a healthy, vigorous stand of grass that is weed-free.

Another benefit of the rest period in irrigated pastures is a reduction in soil compaction. Rest irrigated pastures during and after irrigation until the top several inches of the soil are dry. Soil compaction can also occur if animals are left in the pasture during and after major storm events. Soil becomes compacted when it is inundated with water and heavy traffic or trampling at the same time. This compaction reduces or eliminates the soil’s structure, which has natural channels that carry nutrients, water and air to the root systems of plants.

If a pasture does not have a sufficient rest period, the effects of overgrazing eventually take place. Overgrazing happens when animals are left in one place too long, continually eating the plant re-growth, and not allowing the plant to regain the material lost to grazing. Grasses then become weak which allows weeds to establish in pasture areas.

Therefore, judging the proper amount of rest needed in a rotational grazing system is crucial for a successful, sustainable grazing system. So how do you know when rest is needed?

Judging the Grass for Sufficient Rest

Table 6 lists minimum stubble heights for a few of our common types of grasses.

These minimum stubble heights are what should be standing on the ground when animals are moved out of an area. The pasture area will probably never have that “just mowed” look where all plants are equal in height. But the majority of the plants in a given area should be at or above the recommended height. The area should then be rested until at least double the amount of stubble listed is present. Depending on the season, precipitation, climate and the type of forage present, the rest period can be anywhere between 15 days (with irrigation), and 90 days, if in a drought year with no irrigation water. The key to a successful rotation system is observation.

Complex Rotational Systems

As stated earlier, rotational grazing systems with more pastures containing fewer acres are more complex and productive if used properly. The productivity increase initially is really an increase in harvest efficiency. For instance, if the 10-acre pasture in the above example is split into two five acre pastures with cross fencing, the 1 cow, 2 horses and 1 sheep are forced to compete for the available forage more than they did in the 10-acre pasture. The result is that the animals move away from their comfort zone areas like the barn and water tank, to areas at the edges of the pasture. Plants are thereby grazed, that previously may not have been used.

Complex rotational grazing systems involve pastures that are subdivided into 3 or more cells.

These systems take time to manage and an educated eye. For pointers on how to apply your grazing system please contact your local Extension Service or NRCS office.