By Steve Ensley, DVM, MS, PhD, Kansas State University Veterinary Diagnostic Laboratory,
Scott Radke, DVM; Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, Ames, Iowa,
Simon Timmermans DVM, MS, Veterinary Research and Consulting Services, Hays, Kansas
The purpose of this article is to outline the various analytical tests and capabilities available to veterinarians regarding toxicology and nutrition as well as to aid them in working through toxicological cases in the field.
Analytical and diagnostic capabilities
The toxicology analytical laboratory at the Kansas State University Veterinary Diagnostic Laboratory (KSUVDL) is one of several full service toxicology laboratories in the country. The laboratory has instruments with capability to evaluate a wide range of matrices for a variety of toxic, nutritional, and antibiotic compounds. At KSUVDL, we are expanding our toxicology analysis to include minerals and vitamins in serum, tissue, feed and water, mycotoxins, ionophores, antibiotics, water quality and chemical analyses.
Bovine toxicology case work up
When investigating a potential toxicological case, obtaining a thorough and complete history is the most important initial step. The history of the site should include but not be limited to clinical signs observed, morbidity, mortality, timeline of events, and any recent events that occurred at the site. Typically, in bovine cases involving toxins or poisonings, larger numbers of animals are affected or die within a relatively similar period of time following a specific event, but several infectious agents can act like this as well. The timeline, coupled with clinical signs and recent events, can aid in ruling out certain causative agents.
Careful examination of the surrounding environment and animals themselves while utilizing the four circles approach outlined in Disease of Swine 10th Edition is helpful. Being consistent with this approach helps to reduce the chance of missing a potentially critical aspect to the case. There are several things to note and questions to ask while evaluating the environment, facility, and animals in a toxicology case. Where are affected animals located? Are affected animals sporadic or confined to certain areas of the facility such as a certain pens, areas of the pens or areas of the pasture? What is the appearance of the feed, and is there any abnormality suggesting mold, contamination or medication? Are there discrepancies between groups of animals both environmentally and clinically? Tailor your questions based on clinical signs and list of differentials.
Tissue sampling and diagnostic testing
Based on clinical signs, observations and accurate history of events, you can narrow the list of differentials and decide which samples to collect. Diagnostic samples to consider include tissue, fluids, feed, water, and, at times, environmental samples.
To start a tox case work up, a complete set of fresh and fixed tissue samples is the best initial option for submission. Microscopic evaluation of fixed tissue is a critical initial diagnostic step which aids greatly in forming a diagnosis. The presence of microscopic lesions specific for a certain agent are particularly useful in determining whether feed contamination correlates with adverse health. Considering the more common toxic issues that occur in bovines, specific tissue samples should be collected for diagnostic work up.
Feed and feed-associated cases
As with infectious agents, clinical signs may vary depending on what particular compound, mineral, or vitamin is present or absent within feed while also presenting similar to other etiological agents. Obtain a thorough history in feed-related cases, as time is of the essence for collection of samples, association with clinical signs and potential delayed effects of feed toxicants and minerals.
Collect feed samples for analysis if you suspect ionophore toxicity, mineral toxicities or deficiencies, mycotoxins or suspect feed evaluation of any kind. This feed sample can also be analyzed for chemical compounds. This will also assist in determining from where to obtain samples. Certain agents within feed, whether at toxic or deficient concentrations, can result in lesion formation within tissues. Again, it is important to submit tissues when investigating potential mistakes in feed mixing.
Although feed samples are commonly collected from the feed bunks of clinically affected animals in toxicological cases, consider other samples depending on the case and observe medication use and records due to potential interactions of feed ingredients.
In cases involving accidental medicated feed administration, collect feed from the feed mill, feed storage, feed trucks and feed bunks. In acute cases of feed toxicosis, such as non-protein nitrogen, nitrates, ionophores etc., take samples from feed bunks of clinically affected animals. In suspect cases of mineral or vitamin deficiencies or toxicities, collect feed from multiple areas, mix and place a portion in a one-gallon bag.
Avoid mixing or pooling from different rations or batches as the result will be difficult to interpret and not representative of feed associated with the particular case. Keep in mind that feed samples you take might not match feed ingested by clinically affected animals, since they might have consumed all the contaminated feed. So, obtain feed samples as soon as possible and either chill or freeze them. Rumen samples also do not always represent what suspect feed was consumed. The rumen is not homogeneous and digestion is constantly occurring.
Evaluate the source of the feed to identify potential formulation or delivery errors that could lead to a toxicity or deficiency. Main focus points when evaluating a feed mill include the facilities in general, milling equipment, records, and employees. When examining facilities, question the risk of potential formulation errors. Examination of milling equipment may yield promising results in the event of overflows into bins, electronic or hand mixing errors and malfunctioning or damaged equipment. An example of equipment failure resulting in an ionophore toxicity occurred due to broken load cell that resulted in the continuous leaking of monensin into the feed, leading to adverse health.
Also examine mixing and delivery records to identify accidental feed formulations or accidental deliveries. There are instances in which feed delivery drivers deposit excess feed into a bunk or there is still feed left on the truck and the feed delivery person makes an independent decision to place the feed in a different bunk.
Human error in mixing processes can occur, especially in the case of new employees who are unfamiliar with the differences in premixes. At times, it is not difficult to grab the wrong bag and add it to a ration. Question employees actively involved in the mixing processes to determine if human error potentially played a role. This will also help personnel and the mill learn from mistakes.
In certain situations, drinking water can be the source of death loss. The presence of inadvertently added compounds, cyanobacteria or even medication in the drinking water may be a concern. Water can be analyzed for chemical compounds, nitrates/nitrites, sulfate, total dissolved solids, salinity, pH, coliforms and any other compounds of concern. Multiple sampling points include the well head, middle of the line, and waterers. If surface water is used, the water should be evaluated for specific algae as well. Evaluate water lines, waterers and other associated equipment such as water medicators or additives injected into the water line. Due to analytical requirements, a minimum of 200 mL should be collected in a sealed container.
Legal considerations involving feed-related errors
Legal outcomes involving toxicological cases depend on accurate and legitimate results. Send samples to an accredited veterinary diagnostic laboratory with stringent protocols and quality assurance/quality control measures. An accredited laboratory also serves as an impartial third party that performs the analytical tests, reports and interprets the results. In cases involving an unaccredited laboratory, there is the potential for dismissal of results due to either inadequate testing capabilities or reference ranges.
The herd veterinarian should collect feed samples for submission to an accredited diagnostic laboratory to avoid potential conflicts of interest between producers and feed companies. The samples should not be collected by the producer, employees, or feed company representatives. Collection of samples on-site in lieu of retained feed samples is preferred. The retained samples might not be representative of what the animal(s) received and results may be contradictory to the results of other analytical tests.
Other legal considerations for the veterinarian include:
- Communicate early with your diagnostic laboratory to establish a chain of custody and ensure proper handling and maintenance of samples. Report feed toxicity cases to your state department of agriculture if required.
- Avoid unnecessary diagnostics, which can confuse a legal case. If you establish a definitive diagnosis, cease further diagnostic testing.
- Encourage your client to retain an attorney who is familiar with feed issues.
- Maintain impartiality. Practitioners who are able to remain unbiased and honest throughout a case are more valuable to their client than those who take a side.
- Maintain professionalism through all communication with the clients, laboratory diagnosticians and members of the defense, which could be subject to subpoena. Avoid jokes or sarcasm that could be taken out of context.
- Engage the media with caution. When preforming veterinary and diagnostic duties in the presence of the media, be aware that whatever you say and do may be recorded and presented out of context with negative results. Practitioners can advise clients to not allow media or other unauthorized personnel on the premises.
Bovine cases involving toxicities can be difficult to evaluate, as clinical presentation of several toxicological agents can resemble certain infectious agents. A thorough history with understanding of how toxicities relate to clinical signs, and what samples to obtain, are key to diagnosing a toxicity. We encourage veterinarians to contact a veterinary toxicologist if there is a possibility a case involves toxicity or deficiency, and if they are unsure of which samples to collect, what tests to perform and what treatment or preventative strategies to implement.