Flavones in legume juice are active substances that have a paralyzing effect on rabbit gut (a smooth muscle similar in structure to the muscle of the rumen wall), according to investigators in England. They theorized that flavones might influence the belching mechanism, but we have no direct evidence. Safe grass juice contains small amounts of flavones.

THE THEORY that an allergy might be responsible for bloat was offered by veterinarians in Ireland, who noted a high incidence of bloat following the second dose of trichomonal antigen, a vaccine. The first, or sensitizing, dose had been received 7 to 10 days previously, about the proper spacing for an allergic response. This is an interesting theory and may eventually open up new fields for the study of allergic reactions originating from the digestive tract. It is, however, no more than a theory.

SOME THEORIES are chiefly biochemical in nature. One is that certain toxins that might inhibit belching are absorbed from the rumen. Another, developed in Germany, is that the high phosphatase content of rumen ingesta and the rich phosphate content of bloat-producing plants are responsible for an increased rate of gas production in the bloating animals.

The theories are interesting to research workers but of little practical value to farmers in 1956, but some of them may eventually prove to be very important in the prevention and treatment of bloat.

Heredity is listed as a possible cause of bloat only on limited experimental evidence. A number of bloating steers were sired by one bull. In a limited number of experiments with identical twins, members of the same set showed a tendency to bloat. The importance of heredity as a factor in bloat cannot be ignored. Even if the tendency is inherited, however, it is unlikely that bloating will occur unless aggravated by other factors.

There is some indication that bloat rarely occurs on certain types of soil. Climatic and weather conditions must be involved also, but until the definite substances are found in plants that are responsible for bloat, little can be definitely said regarding the effect of soil fertility and weather.

HOW DOES BLOAT CAUSE DEATH? We do not know exactly. Some researchers assign a physical basis that is, the increased pressure in the rumen interferes with blood flow and respiration and the animal actually dies of suffocation. Others think that absorption of certain gases from the rumen and possibly other toxic substances might be responsible. It is possible that increased pressure may increase the rate of absorption of certain substances that ordinarily might be detoxified or excreted as fast as they were absorbed. Investigations at the New York State Veterinary College at Cornell University indicate that the effects of increased pressures in the rumen may be responsible for a complex set of symptoms.

TREATMENT with turpentine and phenol preparations or coal tar derivatives, commonly used in the treatment of bloat, did not reduce the amount of gas formed. The benefits of such treatments were due to their surface tension defoaming action. A number of American scientists have reported on methyl silicone, another defoaming agent, as an effective treatment in bloat. Such defoaming agents appear to act by changing the surface tension of liquids. Studies in New Zealand indicated that antifoaming agents never failed to protect animals from bloat and to relieve the bloated ones. This should not be interpreted as meaning that all bloat is due to frothing and that antifoaming agents are the complete solution to the bloat problem.

The New Zealand research workers discovered that paraffin, silicones, peanut oil, soybean oil, and turpentine, all of which are surface-active agents, would successfully relieve and prevent bloat. Here, again, it must be remembered that conditions may be different in different parts of the world and that further experimental work will be necessary under the existing conditions in various parts of this country.

It is doubtful even in "frothy" bloat that defoaming agents would be effective in the critical stages of bloat.

In the acute cases, time is of utmost importance so that an emergency rumenotomy would probably be the only effective method of treatment.

In cases that are not critical, the stomach tube method of relieving gas pressure is always worth a trial. In the "frothy" type, however, it may be disappointing, because it is difficult to locate the possible existing gas pockets before the tube, or trocar, becomes clogged.

Extensive work is being done on more effective and efficient defoaming agents. It will be necessary to study the effect of these agents on the rumen bacteria and protozoa and their direct effect on the treated animals. There is little experimental evidence that physical methods or drugs now in use are effective in stimulating belching. It is difficult to evaluate clinical data, as a high percentage of bloated animals recover without treatment.

PREVENTION OF BLOAT should be the primary aim of investigations. When enough basic knowledge is available as to the cause of bloat, it should be possible through feeding and management practices and animal and plant breeding programs to reduce the incidence greatly. If plants are the primary cause and if their chemical and physical characteristics that cause bloat are known, it may be possible to change those characteristics.

Certain feeding practices may offer considerable relief in areas where bloat is a serious problem. There is some evidence that pure legume pastures are more dangerous than pastures that are 50 percent legume plants or less. Weather and other conditions may make it difficult to maintain such ratios.

Bloat occurs occasionally in the feed lot; with the use of fresh, field-chopped legumes, the number of cases may increase. Some feeders control this type of bloat by mixing coarse, nonlegume feed or straw with the roughage. One large feeder puts a bale of straw to every 3 or 4 bales of alfalfa hay through the chopper (dry hay) and believes that it greatly reduces bloat.

Technicians in California reduced the incidence of bloat by feeding Sudan-grass to animals before they were turned on the pastures each day.

Experimental work has started in England on the spraying of harmless de-foaming agents on bloat-producing pastures.

Investigators in Wisconsin found some evidence that common household detergents may be effective in preventing bloat.

FEW DEFINITE recommendations can be made other than the use of mixed pastures and the feeding of coarse non-legume roughages daily before turning on pastures or supplying it to animals on legume pastures. In dry-lot feeding, the inclusion of straw or other nonlegume hay with legume roughage may help to prevent bloat.

Studies of the physical, chemical, and pharmacological characteristics of saponins have been undertaken by scientists of the Department of Agriculture at Beltsville, Md., and Albany, Calif.

The innervation of anatomical structures involved in belching is being studied at the University of Minnesota. Men at the University of Wisconsin began studies of the effect of detergents on foaming and other physical characteristics involved as possible causes of bloat.

The physiology of belching and the place of rumen bacteria in bloat are studied at Cornell University and the University of Maryland.

ROBERT W. DOUGHERTY is professor of physiology in the New York State Veterinary College, Cornell University. He has done extensive research with rumen physiology and bloat. He has published many papers on problems connected with the digestive and reproductive tracts of cattle and sheep.