Coffey Ranch: Total Animal Unit Days (AUD) of Grazing

by Hugh Aljoe, Russell Stevens, Charles Griffith

Total AUDs of grazing has been the standard we use to measure forage harvested on the Coffey Ranch. An AUD is the amount of forage that a 1,000-pound cow will consume in a day. One AUD usually equals about 30 pounds of dry forage. Grazing and feeding records have been recorded for each paddock since the initiation of this study. These records are summarized for native range and bermudagrass, as well as lanes and traps.

Figure 4 illustrates the total AUDs of grazing for each year. The total AUDs are charted as AUDs from (1) native range, (2) bermudagrass paddocks, traps, and lanes, and (3) actual bermudagrass hay production. As Figure 4 demonstrates, total AUDs have increased over time. The most noticeable increase is from the native range paddocks. In the initial year, 1988, approximately 10,500 AUDs were harvested on the native range. The last full year of data, 1996, shows that more than 35,500 AUDs were accumulated on the same area. This is an established threefold increase in the amount of forage grazed by livestock. We attribute this improvement to increased forage production as a result of changes in plant composition through better grazing management.

Figure 4.

Although the herbaceous plant community has yet to reach the desired high-seral state, there has been a dramatic increase in vegetative production. The primary grazing management tool administered was the implementation of the HRM-type rotational grazing method. By developing a series of paddocks and controlling grazing and rest periods, the herbaceous plant communities have begun shifting to more productive, desirable species.

Animal Unit Days (AUDs) per grazeable acre — A comparison between two native range pastures

An AUD per acre is the estimated amount of dry matter that an animal unit consumes each day it is exposed to a unit of grazeable land. AUDs were collected for each paddock throughout each year. Since grazing management was planned for range improvement, the following comparisons focus on the native range pastures.

Figure 5.

In Figure 5, AUDs per acre are graphed for the average of all the native paddocks grazed each year. (Not all paddocks are grazed each year and the number of paddocks increased over time.) The average AUDs per acre of all the paddocks in Pasture 2 (P2) and the AUDs per acre for Pasture 12 (P12) also are shown. The number of native paddocks used to calculate the average for all the native range paddocks has increased from fewer than 30 paddocks in the early years to more than 40 paddocks. Some of the native pastures were originally not fenced separately. Over time we further subdivided pastures into more paddocks, making paddocks smaller.

Initially, P2 was used as a research trial to study the effects of high stock density. During the early years we obtained higher numbers of AUDs in P2 than for the rest of the ranch (Figure 5). Stock densities have increased across the rest of the ranch since because we have further subdivided larger pastures. At present, there is little difference in AUDs per acre between P 2 paddocks and the rest of the native grass paddocks.

P12 was formed in 1992 by separating it from Pasture 11. P11 formed a large grazing paddock with about 42 grazeable acres, and P12 became a paddock with about 18 grazeable acres. In 1992, P12 was broadcast-seeded with a mixture of high-seral plants, including big bluestem, little bluestem, indiangrass, sideoats gramma, switchgrass, johnsongrass, and Eastern gama grass. We found in previous demonstrations that the area was void of seed of high-seral plants. In 1995, a noticeable number of high-seral plants emerged in P12. Those were mostly Eastern gama grass with some johnsongrass and switchgrass. We also observed a few plants of big bluestem, little bluestem, indiangrass, and sideoats grama.

Our grazing management plan has been consistent across the years. We establish rest periods and graze periods annually for each paddock to enhance survivability and productivity of the desired species. The average AUDs per grazeable acre for the native range paddocks has steadily increased from 17 AUDs in 1988 to 47 AUDs in 1996. It is interesting to note that as the number of paddocks increased (indicating more subdivisions, higher stock densities and longer rest periods), the AUDs per acre have also increased. Range conditions improved and allowed us to maintain this upward trend in AUDs over the first 10 years.

On a per acre basis, livestock consumed native range at above 450 pounds of dry matter on average in 1988. This has increased to more than 1,400 pounds of consumed dry matter per acre in 1996 — a threefold increase in nine years.

As shown in Figure 5, P12 was less productive than the average of all the other native range paddocks in the first few years. In 1991 after it was fenced separately, P12 responded immediately to the higher stock density, with the AUDs per acre exceeding that for the other native range paddocks. In 1997, P12 is projected to accumulate between 84 and 92 AUDs per acre of grazing, primarily due to the establishment of Eastern gama grass. A photo of P12 (Figure 6), was taken in the spring of 1997 to illustrate the proliferation of Eastern gama grass.

We estimate that cattle consume half of the dry matter produced in a given paddock. In 1988, P12 produced about 660 pounds dry matter per acre. In 1997, we project that P12 will have accumulated at least 84 AUDs per acre, or about 5,000 pounds of dry matter production per acre.

Coffey Ranch Main Page
The Herbaceous Plant Community
Total Animal Unit Days of Grazing
Stocking Rates
Managing the Woody Plant Community
Wildlife Production