| ||Take home Message | Investigation | Management
This is a fact sheet from the Health Management section of the Alberta Feedlot Management Guide, Second Edition published September 2000. The 1200 page guide is available for purchase on CD-ROM.
Take Home Message
- In spite of good management, unexpected epidemics of disease occur in feedlot cattle.
- An epidemic or outbreak is an occurrence of disease at a much higher rate.
- With feeding accidents, unlike epidemics, many animals are affected suddenly, within one or two days.
- In outbreaks of acute infectious diseases like infectious bovine rhinotracheitis, pneumonic pasteurellosis, or hemophilus meningo-encephalitis (ITEME), the first few cases will be followed by a steady rise in the morbidity rate for several days. This is followed by a decline as the outbreak subsides in 10 days to two weeks after the index case.
- In some cases, the diagnosis may be obvious, e.g., carbohydrate engorgement due to a feeding error. With infectious diseases of the respiratory tract, the cause may not be readily obvious and may require a detailed veterinary investigation. A complete investigation may require involvement of specialists in several disciplines. Every economical effort should be made to determine the cause because it not only improves the efficacy of treatment and control but usually generates new knowledge about the disease, which may be applicable for future outbreaks.
The objectives of an investigation of epidemics of disease are to determine the cause and the extent of the disease and then to take immediate corrective actions and make recommendations to prevent occurrences. These objectives are best achieved by identifying the characteristics of affected and unaffected animals within the study population. It is also necessary to observe, record, and analyse the distribution of the disease with respect to time, place, and a variety of exposure factors and environmental influences. This analysis must be correlated with thorough physical examination and necropsy findings from representative cattle.
A complete history should be outlined. This includes details on the first case (index case), the index date, the total number of sick animals, the treatments given, the percentage of sick cattle which died (case fatality rate), the population death rate (the percentage of all animals which died), and the vaccination history. The origin of the cattle should be determined if possible, and the length of time the cattle have been in the lot may also give some clues to a diagnosis. The composition of the feed and the nature of any recent changes in feeding practices should be determined. A sample of feed consumed by the affected animals should be obtained and analysed or stored for future analysis.
A clinical examination should be done on several representative affected animals. Some normal in-contact animals should also be examined clinically. Frequently, there is evidence of the early stages of the disease in animals that appear normal on a distant examination. In the case of infectious disease, the appropriate samples, such as nasal swabs, blood, cerebrospinal fluid, and feces, should be taken from affected animals and submitted to the laboratory. Necropsies should be done on dead animals as soon as possible after death, before postmortem decomposition makes diagnosis difficult.
When the diagnosis is determined, the rationale for treatment is then outlined. Emergency slaughter for salvage may be the most economical method for the clinical management of diseases such as grain overload. Cattle affected with the common infectious diseases, such as pneumonic pasteurellosis or hemophilus meningo-encephalitis, cannot be slaughtered for salvage, and treatment is necessary. Affected cattle should be suitably identified with an ear tag or black tag and the nature of the treatment recorded. Isolation and separation of
affected animals from the normal population until recovery is apparent in the ideal situation.
When outbreaks of certain bacterial diseases occur, the intensity of surveillance must be increased in order to detect new cases in the early stages of the disease when the response to treatment is usually good. The detection of clinically affected cattle in the early stages of disease is difficult and requires considerable dedication by the pen checkers.
The injection of antimicrobials into all in-contact animals when the total illness or sickness rate has reached 5 to 10% has been recommended. Long-acting oxytetracycline given intramuscularly to all in-contact animals may decrease the daily incidence of new cases of respiratory disease. Regardless of which mass medication system is used, none is totally reliable, and increased surveillance is usually necessary to detect new cases.
As much comfort as is economically feasible should be provided to clinically affected cattle. The amount of bedding should be increased, and protection from snow, rain, or excessive sunshine should be provided. In feeding accidents, the energy level of the feed should be reduced to a level similar to the starting ration. Following successful therapy, the cattle may be reintroduced to the high-energy rations. Refer to the specific articles on those diseases for further details and consult with your veterinarian for recommendations.
All of the details of the outbreak should be listed in chronological order and then analysed and interpreted. This
information can be used to control future occurrences. A detailed report of the outbreak, outlining the conclusion and recommendations, should be prepared and submitted by the veterinarian to the owner.
O. Radostits, DVM, M.S., Dept. of Internal Medicine, Western College of Veterinary Medicine, University of Saskatchewan, 2000. Alberta Feedlot Management Guide.