The belief long entertained that the female acquires the disease at the time of copulation as a result of transference of the infection from affected to healthy females on the genital organs of the bull has failed to receive the support of experimental evidence. The view that the disease is spread to any great degree in this way has been largely discredited. Cows of all ages are more or less susceptible, but young ones in first or second pregnancy most frequently abort. A second abortion is not unusual, and a third may occasionally occur, after which the cow usually becomes immune and thereafter carries her calf to maturity. Heifers from aborting mothers sometimes seem to be less susceptible than others.
Symptoms.—Contagious abortion is a very insidious disease, developing very slowly through several months of the gestation period, and resulting finally in the expulsion of the immature young, this act being simply an indication of the presence of the disease and not the disease itself. Because of this slow development and the fact that the health of the animal is not noticeably influenced, the presence of the disease may not be suspected until it has gained a firm foothold in the herd. The symptoms of approaching abortion are those preceding normal calving. In addition, there may be observed, a few days previous to abortion, a sticky, sometimes purulent, rusty, and odorless discharge. Abortion occurs most frequently from the third to the seventh month, according to the number of abortions, occurring early in first abortion, and later in each succeeding abortion until the calf is carried to full term and the mother has become immune. It happens frequently that calves are carried almost to full term, and are born alive, but are sickly, and soon die. Following abortion there is a dirty, yellowish-gray mucopurulent discharge which persists for two or more weeks. If abortion occurs early, the fetus is passed surrounded by its membranes, but if late in the period of pregnancy, the membranes are retained, decomposition sets in and blood poisoning, which may cause the death of the animal, or sterility may result.
Lesions.—The most characteristic change is found in the uterus where a dark-brown fluid, purulent or even gluey in consistency, and containing grayish-white flakes separates the material membranes from those of the fetus, preventing that intimate contact between the two which is so necessary for the interchange of fluids and gases by which the fetus is nourished and by which it obtains its oxygen. These being cut off, the fetus must of course die. The germs producing the disease are found in greatest numbers at this point. In addition there may be inflammatory changes, first in the walls of the uterus and then in the tissues of the fetus. These inflammatory changes seem most intense in the cotyledons and result in the destruction of the minute structure of those bodies, and they appear swollen, pale, and soft. The membrane of the uterus between the cotyledons also may show inflamed and necrotic patches.
Complications.—Serious results sometimes follow abortion, and this is particularly the case when there is retained afterbirth. The retained membranes decompose, the poisonous products of decomposition and the organisms of decomposition themselves are absorbed, blood poisoning results, and the animal dies. Sometimes, when the animal is able to resist the effects of this decomposition, the uterus becomes the seat of such severe changes that sterility results. The walls of that organ become thickened and hard, the lining membranes become eroded, and conception can not take place. At other times the ovaries, where the reproductive cells originate, become affected and lose their function. Abortion does not invariably follow infection, but the calf is carried to full term. In these cases, however, retained afterbirth is a common occurrence, even to the extent that frequent retention of afterbirth in a herd may be taken as an indication of the presence of the disease. Very often suppurative processes persist for a long time, preventing conception, or sterility may result without apparent cause. A sterile cow is valueless, of course, for any purpose except for beef. Such animals are a source of infection for the others and should not be allowed to remain in the herd.
Diagnosis.—The diagnosis of infectious abortion is made from the changes occurring in the fetal membranes and in the expelled fetus. This, however, is substantiated with certainty only by microscopic demonstration of the germ of abortion. The fact that repeated abortions are observed in a herd is also evidence of the presence of the disease. In consideration, however, of the fact that animals may be affected with the disease and disseminate the germs, even though they carry the fetus to full time, a diagnosis in such instances is only possible by laboratory methods. For this purpose the agglutination and also the complement-fixation tests are being used with splendid results, and by the aid of these biological tests it is possible to determine all infected animals in a herd. The tests are carried out with the serum from animals to be examined, only a teaspoonful of serum being necessary for the execution of both of these tests. It, however, has to be confined to laboratories which are properly equipped for such work.
Treatment and prevention.—It may be said in general that treatment is without avail and all efforts should be directed toward prevention. Various medicinal agents, such as carbolic acid administered subcutaneously and methylene blue fed in large quantities, have been recommended, but have failed to stand the tests of scientific investigation and practical use. Serums and vaccines have also been prepared and sold as cures and preventives, but the work is still considered in the experimental stage.
Bacterial vaccines are at present extensively used in the control of this disease, and while numerous reports indicate beneficial results from their administration, in other instances total failures have been recorded. It appears that the experiments in this line have not progressed sufficiently to justify definite conclusions.
The spread of the disease can be controlled to a great degree by the practice of sanitary measures directed toward the disinfection of premises and the isolation of animals at time of calving and aborting. For methods of disinfection of premises see page 363.
Make frequent observations of the animals of affected herds for symptoms of aborting, such as swelling of vulva or udder enlargement, and upon the discovery of an animal showing these symptoms place her immediately in a stall which is somewhat remote from healthy stock as a means of confining the products of abortion as much as possible should the act occur. If an animal aborts unexpectedly she should be removed to separate quarters and given proper attention as promptly as possible. The fetus, afterbirth, provided it has been expelled, and all litter that has been contaminated with them and uterine discharges should be gathered up and destroyed either by burning or burying. Clean and thoroughly disinfect the floor, gutters, and manger in the vicinity of the aborting animal.
Daily irrigations of the uterus with nonirritating antiseptic solutions, such as 0.5 per cent solution of cresol or compound solution of cresol, at body temperature have a tendency to prevent the multiplication of microorganisms in the uterus and in this way promote recovery. Douching of the uterus should be continued until the discharge ceases. In addition, the external genitals, root of the tail, escutcheon, etc., should be sponged daily with the antiseptic solution.