Steve Morgan, County Agent in Harris County
There are many important components in a successful livestock production system. One of the most important tasks in grazing management is understanding livestock stocking rate. It is critical in making timely management decisions that affect profits in beef cattle production. The optimum number of animals on a pasture makes efficient use of the forage and still leaves enough forage behind to allow a quick and complete recovery. Therefore, producers must understand how to determine the correct stocking rate for their pastures.
Stocking rate is defined as the concentration of grazing livestock on a given amount of land over a season, year or period of time. Generally, stocking rate is expressed as “animal units” for a given amount of land. This is to allow stocking rates to universally cover all livestock types since an animal unit is equivalent to 1000 pounds of body weight regardless of the type of livestock. Though stocking rate depends on the intensity of grazing management, most pastures would be approximately 2 acres per animal unit. This would provide a forage allowance of approximately 2.5% of body weight per day. However, not all livestock have the same forage demand as a 1000 pound lactating cow. For this reason, animal unit equivalents (AUE) have been developed to assist with the approximate determination of forage demand based on the kind, class and size of animal.
Cow – dry 1.00 – 1.50
Cow with calf 1.20 – 1.60
Bull – mature 1.25 – 1.75
Calf – weaned 0.50 – 0.70
Steer/Heifer – 18 months 0.80 – 1.00
Sheep – mature ewe or ram 0.20 – .030
Sheep – yearling 0.15 – 0.20
Goat 0.17 – 0.20
Horse – mature 1.25 – 2.00
The usefulness of animal units is especially apparent considering the weight difference among various producers’ livestock and the fluctuation of average weights in a herd over time. For example, the average cow size varies considerably and has increased over the past 50 years. Today’s beef cow averages around 1300 – 1400 pounds. These cows are not equivalent to one animal unit. In addition, forage demand varies within a livestock species based on its growth rate (e.g. heifers and steers vs. mature cow). For example:
If the estimated stocking rate for a 1,000 pound cow is 2 acres, the estimated stocking rate for the 1,150 pound cow (assuming both cows have the same forage intake rate of 2.5 percent of body weight) is found as follows:
1,150 pounds x 2.5% = 29 pounds forage intake per day ÷ 25 pounds forage per animal unit = 1.16 animal units per cow
Therefore, 1.16 animal units per cow x 2 acres per animal unit =
2.3 acres per 1,150-pound cow
Condition of the pasture impacts stocking rate. Factors such as previous grazing management, forage species, age of stand, soil type, texture, fertility level and moisture conditions all impact forage yield and consequently stocking rate.
Livestock need forage year-round, but providing an adequate supply of forage for grazing 12 months out of the year can be challenging. Ideally, forage production should correspond with livestock needs. However, pasture production is variable during the growing season while livestock nutritional requirements are relatively stable or steadily increasing. One way to balance this equation is to make hay from some pastures during periods of rapid forage growth. In addition, calving before rapid growth will allow the period of highest animal need to match the greatest production of quality forage. A second way is to manage for a more uniform pasture growth. Some Best Management Practices to accomplish uniform growth include:
- Keeping forage healthy and unstressed. These plants begin growth earlier in the spring, produce higher yields through the grazing season and continue growing longer in the fall.
- Switching from continuous to rotational grazing can extend the grazing season and boost yields, since rotational grazing, by virtue of its rest periods, is less stressful to the forage.
- Maintaining a good fertility program will extend the season and boost yields.
Many forage problems can be avoided by fertilizing properly. To determine fertilizer requirements, take regular soil tests and follow the recommendations given. Be sure to state the type of pasture being grown when submitting your sample because fertilizer recommendations will be based on the crop stated. Many producers incorporate grass/legume mixtures to meet more of the fertility needs of the pasture. Seeding legumes into poor quality pastures is the most common form of renovation. Legumes reduce dependence on nitrogen fertilizer, complement grasses by balancing forage production throughout the season, and improve pasture quality.
Switching from continuous to rotational grazing increases forage utilization. Forage utilization is a critical component that helps determine stocking rate. Most pastures contain a great deal of forage that is never consumed and eventually decays. Traditional continuous grazing systems may use only 30 to 40% of the available forage. The rest of the forage is either trampled, soiled, or of little nutritional value because it becomes overly mature. Most of this loss occurs with underutilized fall stockpiles and during periods of rapid growth where there is surplus beyond what is needed for livestock. When the appropriate stocking density is used, shortening grazing periods through rotational grazing increases forage utilization to 60-75%.
Good producers strive to achieve the right balance between forage availability, forage utilization, and animal performance. They stock pastures heavily enough to graze available forage down to a target height that will allow rapid and maximum regrowth without compromising nutritional needs of livestock. Good producers will observe pastures frequently for overgrazing and undergrazing and will periodically adjust the stocking rate or movement of cattle as needed. Overstocking and overgrazing leads to a reduction in palatable plant species and an increase in less desirable plants. Overuse also means that livestock must graze for longer periods to meet their needs. Over time, heavy stocking causes the more palatable and productive forage species to disappear. These desirable forages are replaced by less productive, less palatable plants.