Animal Diseases by L. T. GILTNER VEETERINARIANS and farmers have waged an aggressive fight against animal plagues in recent years. They have kept malignant ones like rinderpest and foot-and-mouth disease, a constant threat from abroad, out of the United States. The worst native diseases, anthrax, anaplasmosis, brucellosis, mastitis, hog cholera, swine erysipelas, tuber- culosis, rabies, and pullorum disease, they held in check by applying approved control plans, including sanitation, vaccination, and treatment with drugs. Some of the vaccines, notably those for preventing rabies and hog cholera, have been improved. All the biological products used in the control work have been maintained at a high standard of quality. Ex- perimental studies on the sulfa drugs have done much to show which infections are amenable to treatment with them. Sulfanilamide, sul- fathiazole, and sulfadiazine are useful in treating some types of strep- tococcal infections, but ineffective against some other bacterial in- fections. Sulfathiazole, sulfaguanadine, and sulfadiazine have value against some forms of dysentery. Sulfathiazole alleviates symptoms of coryza in chickens, although the symptoms reappear when treatment is stopped. Sulfamerazine acts somewhat the same against infectious sinus- itis in turkeys. Sulfamerazine, although having a favorable influence against coccidiosis in chickens, is not effectve aganst lymphomatosis. Penicillin is beneficial, experimentally and in practice, in treating the type of mastitis that is caused by Streptococcus agalactiae. It has shown marked curative eflfect on experimentally induced swine erysipelas infec- tion in turkeys. It was not effective in treating infectious equine anemia, a virus disease, and so far has had no value in preventing or treating other virus diseases. Of course, the sulfa drugs and penicillin, like all 703830°—47 7 81 82 YEARBOOK OF AGRICULTURE new drugs, should be used only as prescribed by a veterinarian; their indiscriminate use may be wasteful and actually harmful to the animal patients. But all this is not to say that we have cured or are about to cure all diseases of animals. Much remains to be learned and done, as the following pages, in which I discuss some of the worst diseases, disclose. Brucellosis of Cattle {Bang's Disease) No disease of livestock has received greater attention from the stand- point of control measures than brucellosis of cattle, or. Bang's disease, as it is commonly called. Years of research have been spent in develop- ing methods of control, and these have been applied in practical field studies. The studies have definitely established that no one system of control is applicable to all herds, but that the choice of method depends on conditions such as size of herd, degree of infection, environment, and whether the herd is for dairy or beef. As a consequence, the Department has approved the use of four methods of control in the Federal-State program for the control of Bang's disease, namely : Blood test and slaughter of all reacting animals ; blood test and slaughter, accompanied by the vaccination of calves; blood test to determine the amount of infection, but retention of reactors until vaccinated replacements are available; whole-herd vaccination. The first plan is the method of choice in small herds and in herds in which brucellosis has been of long standing, that is, where the storm of abortions has passed and the disease has taken on a chronic form. In herds from which certified milk is sold there is no alternative than test-and-slaughter, and this method also is used in the area-plan of control. The second method adds calf vaccination to the first. It has the extra advantage of building a herd that eventually will be more resistant to reinfection, should it occur. Calf vaccination has proved to be a most desirable practice in all herds in which infection is present. The third plan is a good one for herds in which such a large proportion of animals is shown on test to be reactors that their immediate removal, in the absence of suitable replacements, would work an extreme hardship on the owner. Calf vaccination is necessary in this plan and some owners prefer to vaccinate all animals up to breeding age. This plan applies especially to dairy herds in which the milk is pasteurized or sold to creameries, and in purebred herds where the preservation of valuable blood lines is involved. The retention of^ reactors should be considered only as a temporary expedient, to tide the owner over a period until vaccinated replacements can be raised and added to the herd. When replacements become available, the least desirable or profitable reactors ANIMAL DISEASES 83 should be removed from the herd first and this process continued until the herd is free of brucellosis. Three or four years should be enough to establish a negative herd. The fourth plan, whole-herd vaccination, is one of last resort. There are a few herds, called problem herds, in which the infection is of so severe a type, or the animals are so susceptible, that the removal of reactors following repeated tests cannot check the infection. In such herds, vac- cination of the whole herd has had some success. In some herds the pro- cedure has stopped abortions abruptly, but in others no improvement is evident for 6 to 8 months. Whole-herd vaccination has its main advantage in infected beef herds, where a calf crop is a prime requisite. There are several undesirable consequences of the vaccination of adult animals. The vaccinal blood titer, which cannot be told from that of actual infection, may persist for indefinite periods and thus interfere with sales or interstate shipment ; in cows more than 4 months advanced in pregnancy it may cause abortion; and if practiced in dairy cows, a marked drop in milk production may be expected from 10 to 14 days following vaccination. There is little reason to vaccinate all cows in a negative herd. The owner has little to gain, especially in view of the undesirable after-results. On the other hand, calf vaccination, preferably at 6 months of age, is good insurance in all types of herds, infected or negative, against the animal's subsequently becoming infected. The only drawback is that a small proportion of calves may be slow in losing the vaccinal blood titer, which may thus interfere with their interherd movement. The rapidity with which brucellosis in cattle may be eradicated in an infected herd under any of the four plans depends largely on herd man- agement and sanitation. Brucellosis in Swine Brucellosis is spread and perpetuated in swine mainly through the in- fected boar and aborting sow. Recently it has been proved that the causal germ, Brucella suis, is sometimes eliminated in the urine of infected sow^s, and thus further contaminates the premises. Under such conditions the most practical method is to dispose of the entire herd, especially if it is small or not too carefully developed, and make a new start in clean quarters. Replacement animals should be most carefully selected from herds considered to be free from infection. All animals purchased should be negative in all dilutions to the blood test. If valuable blood lines are in- volved, or if the herd is large, success in developing a clean herd has resulted from separating weanling pigs negative to the blood test and rearing them in clean quarters as far away as possible from the infected 84 YEARBOOK OF AGRICULTURE herd. This method should be followed in each farrowing season, with the extra precaution that the separated pigs are tested at intervals of several months until bred. When a clean herd has thus been established, the infected herd should be disposed of and the old premises thoroughly disinfected. Herd boars should be selected with utmost care to avoid reinfection of the herd. Other methods of control, including vaccination, have not proved practical. The infectiousness for man of the germ causing brucellosis in swine is another urgent reason for eradicating the disease. Brucellosis in Goats Except in some herds in the Southwest, goats are quite free from bru- cellosis. During the war, w^hen all sources of food supplies were being utilized, cheese made from goats' milk in the infected sections was be- lieved to have been the cause of several cases of brucellosis in man. Because of the extreme infectiousness for man of the type of brucella affecting goats {Brucella melitensis) ^ all goats producing milk for human consumption should be blood tested. The immediate slaughter of all goats reacting to the test is the only method of control that should even be considered. Mastitis of Cattle Mastitis is undoubtedly the greatest scourge in the dairy industry. Each acute attack causes the loss of milk from the infected quarter until the condition improves, the graduated destruction of milk-secreting tissues and, thus, continued lower production during a lactating period until it no longer pays to keep the animal. Estimates are that at least a fourth of all dairy cattle in the United States have mastitis. Until recently there has been no recognized cure for chronic mastitis. Control measures were of a practical nature—disposing of animals with badly diseased udders, segregating infected cows that were still milking profitably, and preventing the spread of infection to clean cows through strict sanitation in milking and handling the herd. A few years ago drugs were developed that proved to be effective in curing many cases or a high percentage of cases of mastitis caused by Streptococcus agalactiae, the most common cause. The outstanding drugs are sulfanilamide, colloidal silver oxide, tyrothricin, and penicillin. They are infused into the udder through the teat canal. Penicillin, the least irritating of the drugs, will cure a large proportion of streptococcal infections if infused daily in proper dosage for 4 or 5 days.