Robert D. Glock
Colorado State University
There are several reasons for on-going necropsy observations in the feedyard. One is merely to prevent surprises. There is also an element of teaching, which is probably the most important. The information gained by the veterinarian may be far less useful than the information conveyed to feedyard personnel. This includes the frequent observation of misdiagnoses or ancillary conditions that were not detected. It provides a graphic demonstration to crews of things such as retropharyngeal abscesses that were thought to be typical respiratory disease or right heart failures that do not respond to respiratory disease treatments.
We need to encourage more evaluation of injection sites, both by veterinarians at necropsy and by feedlot personnel. Injection site problems are well defined at this point and we need to implement procedures and evaluations to reduce the impact of these blemishes at slaughter.
Necropsies can also be used to demonstrate the dynamics of pneumonia. This is not a static process, and it is important that all recognize that there are many possible outcomes. Understanding these variations can help us do a better job of identifying animals and providing appropriate treatment. This leads into the next topic.
Responses to treatment for respiratory disease are not all or none. There are various outcomes, and the sequence of events in pneumonia from acute to chronic need to be taught to feedyard personnel. Actual lesions can be used to convey information about animals that were pulled too late, animals that failed to respond to treatment, and animals that were beyond profitable treatment.
The process of healing in bovine pneumonias is just beginning to be defined. Recent information varies somewhat with regard to the long-term effects of healed scars involving the lungs. There is an opportunity to study responses and their impact on the economics of the feeding process. This may involve the continued development of better records and monitoring systems.
The so-called brainers in feedlots still remain a problem in various situations. Differential diagnosis is quite dependent on brain removal, and an easy method of brain removal needs to be developed, with this becoming a part of routine procedures. As we differentiate causes of CNS disease in the feedlot, it becomes obvious that the predominant diagnoses will involve polioencephalomalacia (polio) and thromboembolic meningoencephalitis (TEME). Bacterial meningitis is less dramatic and less frequently identified but is nevertheless a very common cause of brain damage and death. We find that Listeriosis is rarely identified.
The most exciting area of advancement in the differential diagnosis of CNS disease involves polioencephalomalacia, which we now recognize as being primarily a condition associated with sulphate levels in feed, water and the rumen. Our older concepts about thiaminase are difficult to confirm in the feedlot situation. Haemophilus (TEME) remains a significant concern. We tend to misdiagnose some cases of bacterial meningitis caused by Haemophilus, Pasteurella or other bacteria because the lesions may be extremely mild and diagnosis may need to be based on bacterial cultures. It is often difficult to avoid contamination.
A ballooning area of interest with regard to the bovine brain involves the diseases classified as spongiform encephalopathies. Monitoring programs are in place, and it is essential that we continue to be alert for the possible emergence of this emotion-provoking disease. Fortunately, this class of disease is unlikely to appear in most feedlot animals because of age. We must, however, be prepared to answer the many questions that may be posed by our associates as well as the public.
This is a very confusing area, and the so-called sudden death syndrome is very difficult to explain in the feedlot. We probably need to do more diagnostic work including monitoring of rumen performance. This may include the use of pH evaluations and perhaps evaluation of other products such as rumen gases. We certainly are not doing a very good job at this point of determining what's happening in this highly volatile environment. It is most likely that the majority of sudden death losses in the feedlot are the result of digestive failures including acidosis, bloat, and perhaps other conditions such as intoxications involving endotoxemia or enterotoxemia.
Another frequent cause of sudden death is atypical interstitial pneumonia (AIP). This baffling and frustrating condition is of unknown etiology, but we need to better define risk factors. This has not been adequately done, and utilization of animal records could be helpful as we become more and more capable of individualizing our observations in the feedlot. Again, there is increasing interest in the concept that AIP may be related to rumen function and may involve the gases that accumulate in the rumen.
Clostridial diseases can be divided into two types systemic and digestive. Necropsy evaluations can be difficult because of varying types, the difficulty of getting good information from the laboratory and the difficulty of interpreting laboratory findings. It's very easy to miss the lesions of blackleg or Clostridium novyi infections because they can be quite localized and our visual observation may be inadequate to find the specific lesion. We also can be misled into assigning importance to clostridia that are present but not causing disease. Insignificant Clostridium spp. can be identified in most carcasses and they are common inhabitants of the digestive tract. Our ability to differentiate this group of organisms is becoming much better, but interpretation is often more philosophical than scientific.
We can now provide DNA-based typing of Clostridium perfringens, which is often blamed for sudden death referred to as enterotoxemia. However, our typing efforts to date indicate that the most commonly identified Clostridium perfringens is type A, and we generally do not associate that with sudden death due to enterotoxemia. We obviously have a great deal to learn, and in the meantime, we lack evidence of the actual occurrence and incidence of clostridial enterotoxemia. We most certainly lack evidence suggesting that immunization is an effective preventive of this condition.
This is a key area that veterinarians must assist the industry with. There is great opportunity for education and monitoring of the entire production system from the cowboy to the management. We most certainly do not have a safety problem in beef production with regard to residues, but we do have a perception problem. This includes things such as blemishes due to injection sites.
Our evaluation of animals in the feedlot can assist in the changes that need to be made with regard to genetics, feeding, pharmaceutical use, and carcass blemishes. We're obviously entering a pretty exciting period where there may be more responsibility placed with the veterinarian to help provide for better selection and use of pharmaceutical agents. This includes acceptance of increased responsibility with regard to dosages and prescriptions.
We need to contemplate the possibility of entering a new philosophical age which is directed more at monitoring the effectiveness of disease prevention rather than monitoring the effectiveness of therapy. The livestock industries in general are learning more about population dynamics and epidemiology. We, as diagnosticians, can help apply some of those principles to the feedlot situation through monitoring of various attempts at disease prevention. So-called biosecurity, when applied in the feedlot situation, simply involves characterization of disease prevention. This may include evaluation and modification of procedures. For example:
Every time we make advances with our ability to provide accurate diagnoses, we also contribute to improved production. This, in turn, improves profitability and product acceptance. One becomes a competent feedlot practitioner or diagnostician not by simple proclamation but by the continued gleaning of bits of information that can be usefully applied in practice. Hopefully these bits of information will lead to better communication between veterinarians and the rest of the production system, with the effect of improving quality and profitability.