Cattlemen generally look forward to the spring of the year. Pasture forages typically begin growing rapidly producing large amounts of lush, green pasture. Unfortunately, given the drought conditions that many areas continue to experience, this is not the case everywhere, but many areas it is.
Rapid grass and legume growth create conditions where cattle can have access to large amounts of palatable, nutritious forages. At the same time, however, conditions come with this that are definite problems and that must be monitored and managed for, in advance if at all possible. This article will briefly discuss two of the most common of these conditions – grass tetany and pasture bloat. Two unrelated but equally problematic situations.
Grass tetany (GT), sometimes called grass staggers, wheat-pasture poisoning or hypomagnesaemia, is a metabolic disorder of cattle related to a deficiency of magnesium (Mg). It occurs primarily in ruminant animals and lactating cows are the most susceptible. Older cows are considered more susceptible than those with only their first or second calves. The reason is thought to be that older cows are less able to mobilize Mg reserves from the bones than are younger cows.
Conditions Leading to Grass Tetany
Grass tetany usually occurs when animals are grazing lush pastures in the spring, but it can occur in the fall and winter. Grass tetany is common during cool, cloudy and rainy weather and often occurs when cool weather is followed by a warm period. Animals get GT most often while grazing cool-season grasses or small-grain pastures in spring or fall. Rapidly growing, lush grasses create the greatest problem. Grass tetany has occurred on orchard grass, perennial ryegrass, timothy, tall fescue, crested wheatgrass, bromegrass, and winter annuals. Small grain pastures include wheat, oats, barley and rye. It also occurs when livestock are wintered on low Mg grass hay or corn stover. Fortunately, GT is not usually a problem on legume pastures (clovers, alfalfa, etc.) or in animals wintered on legume hay.
Grass tetany is most likely to occur on pastures grown on soils that are low in available magnesium and high in available potassium (very common in small grain pastures). Soil testing can provide indicators of potential problems. High rates of nitrogen and potassium fertilizer are sometimes associated with increased tetany problems. Forages should be analyzed when a potential problem is suspected. Forage containing less than 0.2 percent magnesium and more than 3 percent potassium and 4 percent nitrogen (25 percent crude protein) are likely candidates to exhibit GT problems. Forage that is high in potassium and nitrogen also should have at least 0.25 percent magnesium. Some research has also shown that low phosphorus levels can also contribute to increased problems on these types of pastures.
Unfortunately in many cases symptoms are not noted and the only evidence is a dead cow. In mild cases, milk yield is decreased, and the animal is nervous. These signs indicate the need for preventive measures. Animals affected by acute GT may suddenly stop grazing, appear discomforted and show unusual alertness, such as staring and keeping their heads and ears in an erect position. Also, they may stagger; have twitching skin, especially on the face, ears, and flanks; and lie down and get up frequently. At this point, they are easily disturbed and any stimulation may lead to startling reactions, such as continuous bellowing or running. Sooner or later, a staggering gait pattern develops followed by collapse, stiffening of muscles and violent jerking convulsions with the head pulled back. Animals lie flat on one side; the forelegs pedal periodically; the eyes and ears twitch; and chewing motions produce froth around the mouth. Between these convulsions, the animal may appear relaxed. Also during this period, sounds or touching the animal, as when administering treatment, may result in violent reactions. This subsequently results in an increase in body temperature and respiratory rate. Heart sounds become audible. Animals usually die during or after a convulsion unless treatment is given.
Some or all of the following preventative steps may be helpful:
1. Applying Mg fertilizer and dolomitic (high Mg) limestone to the soil may increase the magnesium concentration in plants. The effect of Mg fertilizer or dolomitic limestone is generally greatest on coarse-textured acid soils that are low in potassium. Local recommendations should be obtained before fertilization.
2. Dusting pastures with Mg oxide (MgO) as finely powdered calcined magnesite helps increase the intake of Mg by cattle. Rates of 15 to 30 pounds of MgO per acre are recommended, with the lower rates for pastures where cattle are moved every two or three days.
3. Animals should be fed a high Mg supplement or free-choice mineral (containing 8 to 12 percent Mg.) Magnesium may be added to a protein supplement, silage or liquid supplement. Assuming a 20 percent availability from the supplement, the cow's Mg requirement for maintenance and lactation would be from 13 to 15 grams per day. However, situations may require at least 36 grams to prevent development of tetany in herds. A potential problem with high Mg mineral supplements is low palatability. Magnesium oxide, the primary source of Mg for these situations is unpalatable and getting a cow to eat an adequate quantity in the midst of a high tetany threat situation may be a problem. Magnesium sulfate is also a good source and is more palatable. A better solution is to feed a more moderate amount of Mg on an ongoing basis (include 2.5 to 3.5 percent Mg ongoing) as a preventative. This is especially important in herds having a higher percentage of older cows.
Cows in the early stages of GT should be handled gently, producing the least stress and exertion possible. Driving, roping or anything producing excitement will often result in sudden death. Two hundred (200) mls/cc's of a saturated solution (50 percent) of Mg sulfate (epsom salts), injected subcutaneously, gives a high level of magnesium in the blood in 15 minutes and can be administered by producers under range conditions. Any solution injected into the animal should be sterile, otherwise an infection may be introduced. Therefore, cattle growers interested in using Mg sulfate solution should contact a veterinarian. Other treatments used by some vets include intravenous injections of chloral hydrate or Mg sulfate to calm excited animals and then follow with a calcium-magnesium gluconate solution. Intravenous injections should be administered slowly by a trained person, because there is danger of heart failure if they are given too rapidly. As a follow-up treatment, the animal should be removed from the tetany-producing pasture and fed hay and concentrates. Also, approximately 30 grams of Mg sulfate should be given daily.
One precaution, cows that have GT are likely to get it again later in the season or in later years. Yet, these animals may continue to be high producers.
Bloat is a digestive disorder characterized by an accumulation of gas in the first two compartments of a ruminant's stomach (the rumen and reticulum). Production of gas (primarily carbon dioxide and methane) is a normal result of fermentation processes. The gas is usually discharged by belching (eructation) but, if the animal is unable to remove the excess gas, pressure builds up in the rumen-reticulum exerting pressure on the diaphragm which prevents the animal from inhaling, and bloat occurs. The most common type of bloat is frothy bloat where gas builds up in a foam or froth above the rumen contents and the normal belching is inhibited. Bloat can occur in younger and older animals alike.
Bloat can occur after as little as 15 minutes of grazing. Often the animal bloats only mildly and stops eating. The discomfort is eventually relieved. In more severe bloat, the animal's rumen is distended by ballooning of the rumen, it urinates and defecates frequently, bellows and staggers. Death, due to restricted breathing and heart failure follows unless action is taken.
Bloat can occur on any forage that is low in fiber and high in protein but is most common on immature
legume pastures but can also occur on lush grass pastures as well. This is common with many types of clover and certain varieties create more problems than others. Pasture or “frothy” bloat results from the production of a stable foam that does not allow gas bubbles to form free gas and be "belched" off. The danger of bloat is greatest when pasture plants are young, lush, and high in soluble protein. The disorder is due to the foaming properties of soluble leaf proteins, which are more prevalent in legumes. The essential feature is that rupture of the naturally occurring small gas bubbles is inhibited and intraruminal pressure increases because eructation (belching) cannot occur. Table 1 categorizes a number of different forages by their tendency to cause bloating in cattle. Research has investigated both animal and plant characteristics which affect on incidence of bloat. This research has shown that some cattle can be classified according to their susceptibility to pasture bloat into high or low susceptibility and that this can be passed onto offspring. A number of inherited characteristics are related to bloat. Individual cattle have been classified as having either high or low susceptibility to legume bloat. Highly susceptible cattle typically have larger rumen volumes than “non-bloating” animals. There is a slower rate of passage of particles from the rumen in bloating cattle.
Bloating usually occurs when cattle are first turned onto legume pastures. It seldom occurs on grasses, (or pastures with at least 50 percent grass), coarser pastures, or hay. Bloat usually follows a heavy feeding or grazing period. Animals that are hungry or greedy feeders are most susceptible. This is one reason why, in many cases, a producer will see his “best-doing” cattle are the ones which can develop this condition, due largely to their aggressive eating habits. Other conditions also increase the incidence such as frost, dew or rain on the field. Bloat incidence is likely to be increased during periods of rapid plant growth in the spring or following a summer rain. Also, adaptation of animals to a particular feed is an important factor. Animals may be at increased susceptibility for the short-term due to changes in rumen microflora. As animals become adjusted to a particular pasture or ration, they have less susceptibility to bloat. Cattle that are unadapted to the fresh forage tend to be the most susceptible, i.e. fresh stocker cattle just turned out for gain.
An old wive's tale stating that the risk of bloat may be reduced by waiting until the dew is off the alfalfa is true. A study demonstrated that cattle were 2 to 17 times more often likely to bloat when fed between 7 and 8 AM than when they were fed 4 hours later.
All this being said, most bloat occurs:
• When cattle are first turned onto pastures in the spring.
• When cattle are moved to new pastures if the previous pasture was grazed too short so that cattle are hungry.
• In late summer, during periods of rapid plant growth after rain following a period of drought.
Reducing the Incidence of Bloat
Sound management can help reduce the incidence of bloat. It probably will not eliminate it completely but it can reduce it substantially. Some steps to take can include:
1) Begin grazing in the spring on pastures that are grass or grass-legume (at least 50 percent grass) mixtures. This will allow the animal time to adjust to the pasture.
2) Make sure that the animal is full when first put onto pasture in the spring. This reduces the intake of the fresh pasture until the rumen has had time to adjust to the new feedstuff.
3) Do not start animals grazing when the forage is wet from dew or rain.
4) Start animals on legume pastures gradually. For example, leave cattle on pasture 1 hour the first day and gradually increase grazing time to 4 hours by the third day and day-long grazing by day five.
5) Be sure that fiber is maintained in the animal ration during initial grazing periods. Feed some dry hay or corn silage to grazing animals prior to turning them out to pasture.
6) Check animals for bloat carefully every two hours when beginning grazing.
7) When rotating cattle or sheep among pastures, be sure that animals are moved fast enough so that they are not excessively hungry when going onto fresh pastures.
8) Animals with supplemental feed will be less likely to bloat. For example, a dairy cow, where 40 to 50 percent of the intake is pasture will be less likely to bloat than beef cattle, dairy heifers, and sheep, where pasture comprises 100% of the diet. Stocker cattle receiving at least a couple of pounds of supplement are also less susceptible.
9) Consider using Bloat Guard® (Poloxalene) during periods where bloat is likely. Poloxolene can be mixed with grain supplement or drinking water, drenched, or fed as a pasture block. Effectiveness of this product depends on daily intake. Thus mixing with a daily supplement is more effective than feeding in blocks on pasture. Another useful product is Rumensin® which has also shown efficacy in reducing the incidence of bloating
10) Some animals are chronic bloaters. If a particular animal frequently shows signs of bloat, it may be best to remove that animal from the herd.
Inevitably, no matter how hard you try and how well you manage, you will still, from time to time, encounter some problems with bloating. When bloat is observed, immediately remove all animals from pasture and offer dry hay. This will reduce the bloat problem in all animals that will eat. Forcing bloated animals to walk is also helpful. Bloat
can cause death in as little as one hour so it is important to be prepared to render emergency treatment. When handling an effected animal remember to move them calmly and quietly. As noted, the walking may improve the physical conditions in the rumen causing the animal to eructate, thus releasing some of the gas. If the bloating has not been lessened once you get the animal to the pen then several options are possible. They include:
1) stomach tubing – this involves restraining the animal and passing a rubber hose down it's esophagus (taking care to avoid passing it into the animal's trachea) and into the rumen providing a mechanical release of the gas.
2) Administration of oil – using a vegetable oil drench will reduce the surface tension and allow the gas to escape.
3) Trocar – This should be the last possible consideration and only in the case of a true emergency. Use of a trocar, a device that punctures the rumen from the outside is a rapid and effective means of releasing the gas. It also provides a tremendous opportunity for introduction of infection.
As with many conditions, the best defense is a good offense. It is much more effective to take a proactive stance in the prevention of GT or bloat than have to treat it after it occurs. This is also important because of the rapidity of onset of either condition, in many cases it is too late by the time the producer finds the animal. In most cases prevention involves planned avoidance with the understanding that some isolated incidences may very well occur. Once again, good management is crucial to prevention.
Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org. For more information please visit www. blnconsult.com.