Goats Prove Their Worth
As Range Managers
By: Charles A. Taylor, Jr., Ph.D. and Erika Straka, MSc.
Texas Agricultural Experiment & Research Station
Sonora, Texas (USA)
Since the 1920's the Texas A&M Research Station, located between Sonora and Rocksprings, has been conducting research on the effectiveness of using goats to manage brush. Long-term studies have produced promising results.
Rangelands in Texas and in the West have experienced a significant decline in carrying capacity and ranch productivity as a result of cedar invasion. Cedar trees outcompete more favorable species of browse, forbs and grass for light, water and nutrients. Livestock forage suffers in quality and quantity. Watershed quality is threatened and less rain reaches the soil because of a closed cedar canopy.
Typical control methods include herbicide treatments with Velpar and Grazon PC, mechanical treatments with dozers, grubbers, or chains, fire and biological control with goats.
In many ranching situations the cost of chemicals and mechanical control may not be economical. Using a combination of fire and goats can not only produce remarkable results but may soon be our last resort.
A combination of fire and goats can be very effective in controlling cedar. Also, increasing environmental concern regarding endangered species habitat prohibits mechanical or chemical control in many areas. Concerns for public health and water quality standards will probably limit our use of herbicides in the future.
Economics are important. Mechanical and chemical treatments are often a necessary expenditure to prevent further decline in carrying capacity, but they may not be cost effective.
While using fire may be the initial treatment, goats are the key to ensuring the success of your brush control. Biological control increases the effectiveness, extends the life and increases net returns from your original brush control treatment.
All the cedar was cleared from the Research Station. Pastures that were heavily goated have fewer cedar trees than pastures that were not grazed. Goats will eat cedar primarily in the winter months when there is little else available.
Diet studies conducted on the Research Station show that consumption can go as high as 20 to 30 percent but generally ranges around 10 percent in the winter months and 2 to 3 percent in the spring. An important question to ask is "why don't goats eat a lot of cedar?"
In an attempt to answer this question we steamed distilled cedar samples and analyzed them on a gas chromatograph. We found that monoterpenes are what make cedar unpalatable. Terpenes are plant secondary compounds, which serve as defenses against being eaten by mammals and insects.
There are three different ways that the terpenes may affect the animal as they are consumed. The first mode of action is that they act as chemical signals. Taste buds are nerve receptors that send chemical signals to the brain. In other words, the cedar tastes bad. The second mode of action is that the monoterpenes may have an inhibitory effect upon rumen microorganisms, reducing digestibility.
This has been the subject of several studies and the jury is still out. Some research has shown that oxygenated monoterpenes negatively affected microbes, reducing digestion of dry matter, starch and cellulose. These studies were done in the lab though and not in the animal. Other research has shown that in the live animal there was no significant inhibition.
There probably is a slight negative effect on the microbial population but only when the oils are at very high concentrations. The third mode of action of terpenes in the body is through detoxification in the liver. Terpenes are absorbed into the blood, detoxified by enzymes in the liver and excreted in the urine. This detoxification process might limit the rate of consumption and will be the subject of future studies.
Since we know that intake is limited by the presence of oils, we can over come this limit by decreasing the production of oils in the trees, and by increasing goats' tolerance of the oils.
In order to decrease production of oils in the trees we need to understand why the tree produces oils. Oil production is influenced by species of juniper, individual tree and site (the kind of rangeland the tree grows on).
Considering site first, we know that in a nutrient-limited environment, cedar cannot afford to lose nitrogen and carbon that is tied up in its leaves. Physiologically the tree protects its resources with secondary chemicals that keep the leaves from being browsed off.
A promising area is looking at oil changes in relation to young vs. old plants. In other words, to look at the effect of aging on oil production and palatability, The results back up observations that goats eat the seedlings and regrowth in the pastures. Seedlings and regrowth are much lower in oils than older trees.
Goats will regularly go back to the same trees in the pastures. When the tips are browsed off, regrowth sprouts from lateral buds. This pattern is seen in a larger scale where regrowth sprouts up from a top-killed plant. When these observations were tested in the lab, we found that physiological age of the leaf material greatly influences the amount and kind of oils. Young seedlings and sprouts are much lower in oils and more palatable.
There appears to be a threshold after which leaf material will go from palatable to unpalatable as the oil concentration increases. This has important management implications. If cedar can be maintained below this threshold with control methods such as fire, it will be in a palatable and readily consumable form.
Our second approach to cedar management is to increase the tolerance of goats to oils. In order to accomplish this, we need to know how the oils are metabolized. Metabolism studies were conducted where goats were fed known amounts of cedar, and total feces and urine were collected. The most important thing to look at is the difference between digestible energy (DE) and metabolizable energy (ME) values. This difference between DE and ME represents the loss of the oils in the urine. Oils that are detoxified and excreted in urine are not used for energy. Also note the low crude protein value of cedar. Cedar is not a good forage.
It is important to remember that the emphasis is not on using cedar as a forage for goats, rather it is suppressing cedar with goats. These metabolism studies have laid the ground work for future studies in which we will be looking at how feed additives and nutrition can increase goats' tolerance of oils.
So in summary, our approach to increasing cedar consumption revolves around both decreasing oil production on the one hand, and beefing up tolerance of the oils in the animals on the other hand. What does increased goat consumption of cedar mean for you? It means less cedar, more grass and improved watershed quality.
What steps do you need to take to achieve these results?
- We recommend frequent pasture use by goats so as to take advantage of the window of palatability that seedlings and regrowth experience before they cross over the threshold and become unpalatable.
- Make sure you don't overstock. Year-round goating does not mean year round overgoating. Livestock performance and range quality will suffer.
- Increase grazing pressure (concentration of animals) on target pastures in the winter. Hit the cedar hard when goats will most likely consume it and harm to other plant species can be minimized.
- Provide a supplemental feed if necessary. Juniper alone cannot meet the nutritional demands of goats. Adequate nutrition is also important to meet the demands of detoxification.
- Finally, by properly using critical initial control treatments such as fire, cedar can be maintained in its most palatable state, when goats, or nature's herbicides, can be used as tools to maintain rangeland quality.
About The Authors
Charles A. Taylor, Jr. received a Bachelor of Science (1971), Masters of Science (1972), and Ph.D. (1983) from Texas A&M University. He currently serves as Superintendent of the Texas A&M University Research Station at Sonora, Texas.
Erika Straka received her Bachelor of Sciene degree from Cornell University in 1990; her Masters of Science degree from Texas A&M University in 1993, and is currently working toward completion of her Ph.D. degree in Veterinary Physiology and Pharmacology.
The Texas A&M University System
P. O. Box 918
Sonora, Texas 76950-0918
Phone: (915) 387-3168