Strategies for Selecting Birds for Necropsy, By Kristen-Roza Sutherland, DVM From Boehringer

113

Ensuring poultry flock health is a key to successful production and optimum welfare in commercial operations. A variety of tools can be used to monitor the flock, ensure bird health, and facilitate interventions if warranted. One of the tools commonly used to assess flock health is the poultry necropsy. Necropsy, which requires euthanasia of the bird to allow assessment of all systems and organs of the bird, may be performed as part of a routine session (known as a posting session) or as part of an investigation to determine the cause of sickness, poor performance, or other concern in a flock. Regardless of the purpose of the necropsy, it is critical to select flocks and birds in an appropriate and consistent manner to allow an accurate assessment of flock health, maximize the value of the bird sacrifice, and ensure the validity of any diagnostics.

Routine posting sessions may serve as a key component in poultry health programs by allowing for a health assessment of multiple flocks in a single day. These sessions provide a mechanism to monitor the current poultry health programs and allow for the early detection of illnesses or other issues of concern in the complex. They may also result in proactive changes to poultry health programs to maintain bird health, welfare, and production. It is important to remember there may be some variability regarding the specific parameters for these sessions with respect to producer or specific purpose of the session (i.e. coccidiosis monitoring vs. immune survey). However, there are some useful guidelines to maximize their value. Sessions are scheduled at a consistent frequency, typically every 6-8 weeks. Five or six birds are selected from a targeted flock list based on the overall strategy and objectives. All systems, organs, and tissues of each bird are examined, and gross abnormalities are identified and recorded by flock and age range for reporting purposes and tracking over time.

Consistent flock selection and appropriate bird selection from those flocks are key components for successful posting sessions. A representative sample of 12-15 flocks should be selected based on age, performance, geography, etc. This will allow an accurate representation of flock health and production across the complex. Age range is of particular importance with respect to flock selection. Usually, flocks age 14 days to processing age are selected with each seven day age range equally represented if possible. For example, two flocks age 8-14 days, two flocks age 15-21 days, two flocks age 22-28 days, etc. until processing age. However, age range selection may vary due to customer preference, objective of the session, etc. Once the flocks have been selected, how do you select the right birds? The key here again is selecting a representative sample of the birds from each flock. The birds selected should be “normal” for the flock. They should not be the first 5-6 birds caught just inside the door, not the “poor doers”, nor the “best of the best” so to speak. The birds should be a fair representation of “normal” for the flock to allow an accurate assessment of flock health and performance.

While routine posting sessions are valuable for health monitoring and early detection of challenges, statistically, they may not provide an adequate representation of the health of the entire poultry population in a complex. A targeted investigation into a known “problem” flock is often needed to provide the complete picture of bird health. Poultry necropsies are performed as part of an investigation due to a suspected disease, poor production, or other concern in a flock. As expected, the objectives of these investigations vary significantly from those for routine posting sessions. These investigations virtually always include targeted sample collection and diagnostics to identify a definitive cause of the issue of concern. Therefore, flock and bird selection as part of these investigations are considerably different when compared to routine posting sessions.

When looking to identify a specific illness, proper flock selection is crucial to the investigation’s success. Paying attention to the expected geographic spread of a disease and using that when choosing flocks to examine can be helpful in an investigation. An example of this would be choosing an already affected flock and a close neighbor for sampling. When doing this, it is very important that you visit the sick flocks last to avoid being a carrier for disease to spread.

Once flocks are selected, unique methods are required to assure the best chance of finding diseased birds when compared to selecting birds for routine posting sessions. In most diseases affecting commercial poultry, not all the birds in a flock will be positive for that disease at the same time. Because of this, it is important to strategically choose birds from a flock that will provide the team of service personnel and veterinarians the best chance to find the underlying disease. Three groups of birds should be considered for necropsy in this situation. First, live birds showing clinical signs should be collected. The majority of birds being examined should be in this group. Second, a few apparently healthy birds should be collected. Lastly, fresh dead may be collected. It is important that these birds be recently culled or naturally deceased due to the clinical signs of interest.

A final consideration for sampling in a disease investigation is attention to the timeline of disease and what types of diagnostic testing you would like to use. Testing for the disease itself (like PCR or culture) would be most successful in flocks early in an outbreak. Antibody testing (like ELISA) is more likely to provide true results 10+ days after the initial clinical signs were seen, to allow time for antibody response. If a method of investigation and testing has already been chosen, identifying birds that fit the above timeline is important for the best chance of accurate testing results.

Necropsy as part of routine posting sessions or investigations is an important tool in maintaining flock health. Bird sacrifice should always be approached conscientiously and by choosing the least number of animals needed for accurate and swift identification to the root of problems. In routine posting sessions for health assessment, choosing a representative sample of multiple ages, flock quality, and other variables seen in the field will help to provide the most accurate picture of overall health and assist in rapidly identifying areas for improvement. In necropsy for disease investigation, both healthy and sick birds are needed for comparison and most likely identification of the origin of the concern. Using the principles outlined in this article can help guide flock and bird choice and assure best chances of success in using poultry necropsies for health monitoring and investigations.