Pneumonia Rises when Temperatures Fall
Posted: February 10, 2010
Cattle are predisposed to pneumonia. Their lungs are relatively small when compared to other large grazing animals (horses). They tend to breath at a much faster rate and their upper respiratory tract is not especially well equipped immunologically to trap and kill bacteria and viruses in the air. Even under ideal weather and housing conditions pneumonia is often just around the corner. The 2007 Dairy NAHMS identified pneumonia as being responsible for 24.5% of all pre-weaned calf deaths and 44.8% of all post weaned calf deaths. Cold weather tends to promote concentration of animals and less than ideal ventilation leads to the accumulation of noxious gases, as well as bacterial and viral pathogens. This is not new and problems tend to be better or worse year to year in various areas around the state.
Recently a number farms in south western PA have reported problems with pneumonia and sudden death in cattle. While not every case has been exactly the same there are a number of common factors shared. There are also some preventative measures which could help many beef and dairy producers avoid similar problems.
BVD type II has been identified in many of these pneumonia herds in PA. While many different BVD strains can cause disease some strains tend to be more virulent. Many of the most virulent strains are in the Type II category. A hallmark of BVD infections is that while the animal is infected the virus can destroy many/most of the circulating white cells in the blood stream. This makes the animal extremely vulnerable to other infections, especially the bacteria that cause pneumonia.
The virus can be carried and spread in a number of ways. Animals that are actively infected can have virus throughout their bodies and pass the virus in virtually any secretion or tissue. During active infection, the virus can be found in saliva, mucous, sometimes milk, tears, semen, and at least for a few days under reasonable climatic conditions, on nearly everything in barn that the animal has touched. This includes feed troughs, waterers, milker inflations, and even on cow beds. An infected animal can spread billons of virus particles. Depending on the BVD strain, some infected animals can become very ill and some die despite aggressive therapy. Animals can also have transient infections even if they have been immunized. Here they tend to have the virus circulating (usually at much lower levels) but they do not exhibit any clinical signs. Excellent immunization programs with high levels of protection can minimize or virtually eliminate transient infections.
The classic carrier for BVD is the persistently infected (PI) animal. In this case the calf is infected in utero (~40 to 120 days) and is born with the BVD virus throughout its body. This animal is incapable of clearing the virus and is always (persistently) infected. A calf or two like this going through a sale barn or riding on a truck or trailer can be a biosecurity nightmare.
If producers do not employ reasonable biosecurity practices and immunization protocols on their farms, periodic outbreaks of BVD and pneumonia will occur. The combination of BVD and bacteria like Manheimia hemolyticium can be especially deadly. Cattle can become so acutely ill that they die suddenly, sometimes in less than a day. BVD virus can destroy white cells, rapidly dividing cells or platelets so efficiently that the animal literally collapses. Manheimia can cause so much fluid accumulation in the lungs that the cow or calf literally drowns. In these cases, even with aggressive and expensive therapies, it may be impossible to save the life of the cow. A further complication of this scenario is concurrent infection with mycoplasma species.
Many cattle are non-clinical carriers of mycoplasma. At times mycoplasma can be a primary pathogen and in many cases following bacterial pneumonia and treatment, mycoplasma will increase in virulence and spread. In infected animals mycoplasma often can be found in the lungs, joints, middle ear, and secretions including milk. Mycoplasma infections are extremely difficult to treat or eliminate. Once the infection is in joints or the middle ear or the udder, most veterinarians recommend culling the animal. This is a frequent recommendation even for young calves or animals that appear normal but have the organism in their udder. Mycoplasmas are not sensitive to the ß lactam (penicillin like in structure) antibiotics, nor do mycoplasmas grow under routine microbiological conditions. Producers frequently become frustrated. They treat and treat animals, none of the typical antibiotics work and nothing grows on culture.
While all herd pneumonia cases cannot be eliminated, an effective biosecurity plan and an effective immunization plan can greatly reduce the risk of these fulminate pneumonia outbreaks. New animals should be separated or quarantined from the herd for at least 2 weeks after arrival. If at all possible, 4 weeks of quarantine would be better and closer to the ideal. This can be hard at times, but at the very least new animals can be housed together in one string, or at one end of the barn to minimize contact. Water and feeding areas should be separated. Producers should review air flow and farm traffic patterns so that clean areas and cattle are taken care of first before moving to areas where new or suspect cows are housed. Any animal that becomes ill needs to be thoroughly evaluated, treated as soon as possible, and have appropriate tests taken to diagnose the problem. This is especially important after new animals have been brought on the farm. Serious infectious agents are much more economically contained the sooner the offending organism is identified. Finally, if closed herds cannot be maintained, it is very important that newly purchased animals are selected form herds with solid herd health preventative plans. Plus the existing herd at home should be well immunized and have adequate boosters well in advance of the arrival of any new animals. Purchased animals should be pre-conditioned with immunization protocols that include adequate boosters. Animals should be adapted to a similar diet, and not be stressed through the trucking process. It is certainly in the animal’s best interest as well as in the producer’s best interest to prevent rather than react to disease problems.
BVD and pneumonia have been around the state for years. When serious outbreaks occur, in most cases fundamental animal care, animal health and animal environment conditions are not what they should be. Basic biosecurity, clean air, a comfortable dry bedding area, adequate immunizations, and appropriate diet are fundamentals that simply can’t be skipped or short changed without risking animal health.
A few fundamentals of an effective immunization program will be discussed in the next issue.
David R. Wolfgang, Extension Veterinarian, Department of Veterinary and Biological Sciences