There are many infectious diseases in beef cattle that cause economic losses to the cow-calf producer through death loss, treatment costs or abortion. Many of these diseases can be prevented by proper management and vaccination. Becoming familiar with the diseases most common in your area, then following up with the proper health program are essential to maintaining a healthy herd.
BRUCELLOSIS or Bang's disease, is the most common cause of abortion in cattle worldwide, except in countries where it's been controlled by vaccination. Incidence of Brucellosis in U.S. cattle was 11.5 percent in 1935, before wide use of vaccination, but dropped to less than 0.5 percent with diligent vaccination programs. Brucellosis continues to be a minor problem, if all female cattle are vaccinated as calves. Because of the threat to human health, a rigorous program to eliminate the disease in cattle was begun as soon as a vaccine was developed for cattle. Some states are now Brucellosis-free, but in other states, all heifer calves must be vaccinated before they are 10 months old, and no cows or heifers can be sold or shipped out of state unless they've been vaccinated.
Natural hosts are cattle, hogs, goats, bison and elk. The disease in U.S. cattle will never be completely eliminated as long as there are problems in wildlife. Bison and elk in Yellowstone Park, for instance, carry Brucellosis and pose a threat when they come out of the park and mingle with cattle or contaminate pastures.
Brucellosis in cattle causes abortion in the last trimester of pregnancy and results in a subsequent period of infertility. Any cattle suspected of having the disease, or any new additions to a herd that have no evidence of calfhood vaccination (tag or tattoo in the ear) should be tested. If a cow aborts or calves prematurely, and you suspect the possibility of Brucellosis, consult your veterinarian. Wear protective gloves when handling the animals, and scrub well afterward, advises Dr. Heidi Smith, veterinarian at Terrebonne, Oregon. Don't touch your eyes, nose or mouth after touching the newborn calf or fetus. Burn or bury any aborted fetuses or placental tissues. This problem can be avoided if you buy only females that had calfhood vaccinations, and vaccinate all heifers within the proper age limit. Brucellosis is preventable, but as long as wildlife harbor it, there will always be some risk.
LEPTOSPIROSIS -- The most common cause of infectious abortion in cattle today is leptospirosis, caused by a bacteria that affects many kinds of animals-spread by urine of sick and carrier animals who contaminate feed and water. The bacteria can enter a cow through breaks in the skin on feet and legs when walking in contaminated water, says Smith, or through nose, mouth or eyes by contact with contaminated feed, water or urine.
The disease in cattle may be mild or severe, according to Smith. About 70 percent of infected cows show little sign of sickness, while about 30 percent may show fever, loss of appetite, drop in milk production, jaundice, anemia or difficult breathing. In severe cases, the cow may die. Young cattle are often more severely affected than adults. After recovery from the acute period of illness, the animal sheds bacteria in its urine for several months, remaining a source of infection for other animals. The bacteria affects unborn calves; a pregnant cow will usually abort one to three weeks after recovering from the acute stage of the disease. Even if she didn't seem sick she may abort. Lepto abortion in an exposed herd may vary from five to 40 percent depending on the number of susceptible cows. Not all infected cows abort. Sometimes an infected cow will give birth to a live, weak calf that dies a few days after birth.
Recovered animals are immune to the type of lepto that caused the illness, but still susceptible to infection from other types, of which there are more than 40. There is a vaccine effective against five of the common types of lepto that cause abortion in cows, giving immunity for about six months. For good protection, cows should be vaccinated twice a year, according to Dr. Robert Cope, veterinarian at Salmon, Idaho, since lepto can cause abortion at any stage of pregnancy. The vaccine is inexpensive and should definitely be part of a vaccination program, he says. If an "abortion storm" occurs, cows may abort on a daily basis.
"Even immediate vaccination takes time to take effect, so several more abortions can occur before immunity develops. Prevention is obviously preferable," says Cope.
The disease can be introduced into a herd by purchasing an infected cow, from pigs mingling with cattle or from contact with infected wildlife or rodents. Even if cows never come into contact with other cattle, they can get lepto from dogs, mice, wild ruminants (deer, elk, antelope, etc.) or other carrier animals urinating on a feed ground or contaminating feed or water.
IBR -- Another common cause of abortion is infectious bovine rhinotracheitis or "red nose." Abortion is easily mistaken for lepto, says Cope. IBR is one of the most common viral infections in cattle and can spread rapidly when cattle are confined in groups, often causing upper respiratory disease (red nose), and sometimes secondary pneumonia. IBR can cause serious cases of pneumonia when complicated by bacterial infections, he says. The virus can also cause inflammation of eyes, or diarrhea in calves.
Some animals carry the virus even when seemingly healthy, and periods of stress or other diseases may reactivate the infection and result in transmission of the virus to other animals.
Symptoms of the respiratory form include high fever (104 to 107 degrees), red nasal membranes, ulcers in the nose, throat and windpipe, coughing, inflammation of muzzle and nostrils, loss of appetite, rapid or difficult breathing, dullness, profuse nasal discharge-which is clear and watery at first, then sticky and yellow, hanging from the nose in long strands, says Cope. There may be a watery discharge from the eyes that becomes sticky as inflammation of the eyelids develops. All animals in the group may be infected, and many will cough. They eventually recover unless the disease is complicated by secondary infections due to weather stress.
