On this episode of Tox Talk, Dr. Brad White and Dr. Scott Fritz discuss a case where eight bred cows were moved into a barn ahead of a winter storm and were found dead the next morning. While initial concerns focused on the barn environment, testing revealed the cause was acute nitrate poisoning from newly introduced millet hay containing high nitrate levels. Nitrate toxicity can cause rapid death, often within hours, and may leave few obvious signs. This case is a reminder to consider what has changed when sudden losses occur, especially feed sources. Certain forages, including millet and other stress-grown crops, can accumulate nitrates, and toxicity persists after baling. Testing unfamiliar or newly purchased hay can help prevent devastating losses.
In this Tox Talk episode, Dr. Brad White and Dr. Scott Fritz review a case involving six dead calves out of 38 fall-calving cow–calf pairs on pasture. The producer had not been checking the herd frequently, making the exact timeline of deaths unclear. With at least one calf estimated to have been dead for 4–5 days. They emphasize how decomposition, weather, and time since death affect necropsy value. Initial differential diagnoses focus on infectious causes and potential toxicities, given that only calves were affected.
A 2,000 cow dairy is seeing high culling rates due to lameness but not the typical lameness they are used to. What is wrong? Dr. Brad White and Dr. Scott Fritz will discuss.
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley, and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producers in the field.
When a large dairy operation finds seven young calves dead, they seek help from the toxicologists. What happened and how can they prevent it from happening in the future? Brad White and Scott Fritz go over this case and answer those questions. Thanks for listening!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
For this unique episode of Tox Talk Dr. Brad White and Dr. Scott Fritz walk through how to collect samples to send into toxicology. They will discuss the important samples to collect depending on the situation. Toxicology Sample Collection Guide
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
ESSENTIAL Samples These are your non-negotiables — collect them in nearly every case of suspected toxicosis.Â
Â
Rumen Contents
Amount: Gallon bag mixed from different compartmentsÂ
Container: Clean, leak-proof plastic container (NO additives)Â
Storage: Refrigerate or freeze ASAPÂ
Why it matters: Primary exposure site for many toxins—contaminated feed, plants, heavy metals, etc. Snapshot of recent intake.Â
LiverÂ
Amount: 1 poundÂ
Container: Plastic bagÂ
Storage: FreezeÂ
Why it matters: Metabolizes and can bioaccumulate toxins, first-pass metabolism means liver often has highest concentrations following oral exposure. Include formalin-fixed sample for histopathology.Â
Kidney Â
Amount: One whole kidney (or sections from both)Â
Container: Plastic bagÂ
Storage: FreezeÂ
Why it matters: Often contains the highest concentrations following IV exposure, also main route of excretion. Many toxicants can cause microscopic lesions here so include sections fixed in formalin.Â
Ocular FluidÂ
Amount: 1–2 mLÂ
Container: Red-top or plain tube (no additives)Â
Storage: RefrigerateÂ
Why it matters: Blood degrades quickly, ocular fluid is more stable postmortem. Ideal for nitrate, ammonia, electrolytes. Subject to postmortem change especially if left in the globe.Â
Feed and Water Samples
Amount: Gallon bag, 16 oz waterÂ
When mixed rations are suspected, include samples of mix as delivered and individual componentsÂ
Container: Clean plastic bags or bottlesÂ
Storage: Refrigerate or freezeÂ
Why it matters: Needed to confirm exposure source. Test hay, silage, grain, minerals, water, etc.Â
Formalin-Fixed Tissues
What to collect: Liver, kidney, brain, heart, lung, abomasum, rumen, muscleÂ
Container: 10:1 formalin to tissue ratioÂ
Why it matters: Some toxins cause identifiable lesions—centrilobular necrosis, renal tubular injury, myocardial necrosis.Â
OPTIONAL / CASE-BASED SamplesÂ
Collect when relevant to history, clinical signs, or herd investigation scope.
Heart
Amount: WholeÂ
Container: Seal proof bagÂ
Storage: Refrigerate or freeze fresh, also fix in formalinÂ
Why it matters: Essential to demonstrate lesions for ionophores, selenium, some cardiotoxic plantsÂ
Urine
Amount: Whatever you can getÂ
Container: Sterile containerÂ
Storage: Refrigerate or freezeÂ
Why it matters: Good for water-soluble toxins and early/sublethal exposures, hypomagnesemia – need to correct for creatinineÂ
Brain
Amount: Whole or large portionÂ
Container: Bag for frozen, formalin for histoÂ
Storage: Freeze for chemistry, fix other half for histologyÂ
Why it matters: Needed for sodium testing or neurotoxins, acetylcholinesterase activity, and demonstrating lesionsÂ
Fat
Amount: HandfulÂ
Container: Plastic bagÂ
Storage: FreezeÂ
Why it matters: Stores fat-soluble compounds, sometimes for years.Â
Skeletal Muscle
Amount: 100–200 gÂ
Container: Plastic bagÂ
Storage: Formalin, need fresh for drug residuesÂ
Why it matters: Essential for ionophores, selenium, etc.Â
Abomasal Contents
Amount: 100–500 mLÂ
Container: Plastic containerÂ
Storage: Refrigerate or freezeÂ
Why it matters: May provide more concentrated contents than the rumen, especially in calves.Â
After a big thunderstorm some calves are found dead and some found sick. What caused it and why were the cows not affected? Dr. Brad White and Dr. Scott Fritz will find out in this episode of Bovine Science.
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
After a large snow storm 34 cows have aborted their calves. What caused this and how can it be prevented in the future? Find out on this episode of Tox Talk a Bovine Science Podcast with Dr. Brad White and Dr. Scott Fritz? Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
When this producer goes to move his heifers he finds one dead and others ill. With no obvious clues, what caused the heifer to die and could this happen to the others? Find out on this episode of Tox Talk a Bovine Science Podcast with Dr. Brad White and Dr. Scott Fritz? Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
Four dead calves found in a pasture after being turned out for the spring. What caused it, and why were no cows affected? Find out on this episode of Tox Talk a Bovine Science Podcast with Dr. Brad White and Dr. Scott Fritz? Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
After moving 700 pound stocker cattle to crop residue the producer found eight of them dead. What caused it, and can they put animals out there again? Find out on this episode of Tox Talk a Bovine Science Podcast with Dr. Brad White and Dr. Scott Fritz? Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
This producer moves his cows out to cornstalks and the next day gets a big snow. When he goes to check on them the next day there are 14 dead. Dr. Scott Fritz and Dr. Brad White get to the bottom of the case in this episode. Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
As this producer gets ready for the snow they discover that 11 of their cows are lame. What caused it, and how can they keep the other 30 cows from going lame? Find out on this episode of Tox Talk a Bovine Science Podcast with Dr. Brad White and Dr. Scott Fritz? Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
In order to gain some weight 16 cows are put in a dry lot on feed, one morning the producer sees they haven’t eaten and the next morning 8 of them are dead. Dr. Scott Fritz and Dr. Brad White get to the bottom of this case in this edition of Tox Talk: a Bovine Science with BCI podcast. Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
In the initial call Dr. Scott Fritz receives a box of cattle to determine what caused 30% death loss after heifers were put out on grass. Find out how they got to the bottom of this case on this episode of Tox Talk with Dr. Brad White and Dr. Scott Fritz. Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
Yearling heifers are found walking odd after being moved to a grass pasture. Dr. Scott Fritz and Dr. Brad White get to the bottom of this case in this edition of Tox Talk: a Bovine Science with BCI podcast. Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
After a normal pasture rotation the next morning most of the herd is found dead. Dr. Scott Fritz and Dr. Brad White analyze this abnormal case and discuss the necropsy process leading to diagnosis in this edition of Tox Talk: a Bovine Science with BCI podcast. Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.eduÂ
Sources
Warm, stagnant, surface water, often with a mechanism of phosphorus and nitrogen loading. Algae may appear as a scum on the surface that resembles paint. These blooms are buoyant and often concentrate on the downwind side of ponds.Â
Mechanism
Hepatotoxic algal toxins disrupt the microstructure inside hepatocytes resulting in acute, severe hepatocellular necrosis.
Neurotoxic algal toxins cause a severe neuromuscular blockage.
Signs
The most common clinical signs observed is acute death. The neurotoxins produced by these algae are some of the most potent biotoxins known and can result in death in minutes. The hepatotoxic varieties are the most commonly-encountered in most places where cattle production occurs. Death from exposure often occurs in 24 hours. Clinical signs, if observed, are typically non-specific. Animals may only appear depressed which progresses to tachypnea with signs of abdominal pain and death.
Treatment
Due to the severe nature of the exposure, effective treatments have not been identified. Once animals show clinical signs, a lethal dose has likely been consumed.
Diagnosis
Identification of algae and toxins in water sources, histopathology of the liver.
Fritz, S. A., Charnas, S., & Ensley, S. (2024). Blue Green Algae. Veterinary Clinics of North America: EquinePractice, 40(1), 121-132. doi:https://doi.org/10.1016/j.cveq.2023.10.006
Two 10-year-old cull cows were placed into a small pasture to put some weight on before going to town. Two weeks later, they are both dead with no clinical signs of disease. Dr. Scott Fritz and Dr. Brad White get to the bottom of this case in this edition of Tox Talk: a Bovine Science with BCI podcast. Thanks for tuning in and enjoy the show!
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.eduÂ
Sources
Calves are usually affected due to dams being deficient in vitamin E and/or selenium during gestation. Selenium is naturally found in grains and forage. However, certain areas of the country such as the northeast, eastern seaboard, and northwest are known to have deficient selenium levels in the soil. Vitamin E is normally found in high-quality hay, silage, and green forage. Supplements containing vitamin E can also be administered. Selenium is legally regulated in feed supplements due to its toxic potential.
Mechanism
Vitamin E and selenium act as antioxidants and protect cells from damage caused by free radicals. Without this protection, heavily oxygen-dependent cells like cardiac and muscle cells are injured or die.
Signs
Animals with primarily skeletal muscle damage can show an altered gait, muscle weakness, difficulty rising, and pain on palpation.
Animals with primarily cardiac damage can show respiratory stress, difficulty breathing, and a buildup of fluid in the abdomen due to heart failure.
Treatment
Supportive care is necessary to make sure the animal is stable. Once stable, supplementation of vitamin E/selenium should be administered to the affected animal. Injectable selenium and vitamin E supplements are available for short term use. The diet should be evaluated to make sure appropriate amounts of vitamin E and selenium are present to avoid further deficient animals.
Diagnosis
Vitamin E ïƒ serum (red top tube) or fresh/frozen liver
Selenium ïƒ whole blood (purple top tube) or fresh/frozen liver; feed samples can also be analyzed
Two months into the calving season, multiple calves within a 40 head herd randomly die with no clinical signs. Dr. Scott Fritz and Dr. Brad White get to the bottom this mystery on this week’s edition of Bovine Science’s Tox Talk.
The toxicology website and Bovine Sciences with BCI podcasts have been sponsored in part through a veterinary services grant that Dr. Scott Fritz, Dr. Steve Ensley and Dr. Bob Larson have received to share more toxicology information and examples for people to understand what to submit and how to submit. Another part of that grant has been working with people and producer in the field.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.eduÂ
Sources
Feed, Protein Tubs, Fertilizer-contaminated water
Mechanism
Rumen urease cleaves urea making ammonium, that reaction causes the rumen pH to climb. At pH >8, the reaction selects for ammonia that is absorbed and transported to the liver. The liver’s ability to metabolize ammonia is overwhelmed leading to hyperammonemia.
Signs
Rapid onset (20-60 minutes) of uneasiness, bloat, dyspnea, recumbency, paddling, cyanosis, and death. The rapid progression from consumption to death precludes the formation of any reliable lesions. Rumen pH will typically remain elevated for ~24, pH paper is a cheap and effective way for in-field evaluation.
Treatment
Treatment is based on lowering the pH and diluting the urea concentration. The most effective way to accomplish this is a rumen infusion of acetic acid (vinegar) and cold water. Animals should be triaged with treatment directed towards clinical animals that are not yet recumbent. Survivors generally have no lasting effects.
Diagnosis
Post-mortem diagnosis is based on ammonia concentrations in ocular fluid as well as rumen pH. Rumen content should be frozen ASAP because the ammonia will volatize off the sample.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.eduÂ
Sources
Primarily a water deprivation syndrome – cattle can consume a significant amount of salt if fresh water is available. There are reports of mineral-starved cattle overeating mineral supplements with sodium used as an intake limiter.
Mechanism
As animals become dehydrated, the sodium concentration in the brain increases. The problem is upon rehydration, water follows the sodium into the brain resulting in cerebral edema and death to neurons.
Signs
Clinical signs are the same for lead poisoning and polioencephalomalacia and rooted in the central nervous system. Blindness is a hallmark of the syndrome and can help rule out causes of neurologic disease in cattle. Ataxia, head pression, recumbency, and death are also associated with the progression of clinical signs.
Treatment
The classic therapy for polio cases is injectable thiamine. Thiamine is a general neuro-protectant but is less effective in water deprivation cases than polio and lead encephalopathy. Slow rehydration of affected animals is the best approach. This can be a challenge on a herd basis and veterinarians and producers are often forced to get creative. Unlimited access to water will precipitate clinical signs and IV fluid therapy is not practical. Allowing water to run on a flat surface and forcing animals to drink slowly is ideal. Fluid deficits should be corrected over 12-24 hours.
Diagnosis
Diagnosis is based upon clinical signs, lack of a response to thiamine, characteristic lesions in the brain, and elevated brain sodium levels. It is important to submit both fixed and fresh brain in these cases as formalin-fixed brain is useless for sodium evaluation.
Scott Fritz, DVM, ABVT ToxicologistBeef Cattle Institute Kansas State University Scottfritz@vet.k-state.eduÂ
Sources
Alfalfa is the most common source of phytoestrogen exposure in the US. Other clover species can contribute to the total exposure.
Mechanism
Phytoestrogens bind to estrogen receptors in the animal leading to multiple effects.
Signs
The most economically important clinical sign associated with phytoestrogens is infertility. This is especially true in pre-pubescent animals that are exposed and can lead to life-long infertility by disrupting the estrogen-influenced maturation process. Prolapses have also been associated with feeding high levels of phytoestrogens. Phytoestrogens do not cause abortion.
Treatment
Remove the suspect source.
Diagnosis
Phytoestrogen evaluation of suspect feed source. Clinical improvement following removal.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.eduÂ
Sources
Plants are typically fertilized, and drought-stressed, occasionally herbicide-treated plants can become more palatable and cause problemsÂ
Plants (Johnson grass, corn stalks, Sudan grass), water (especially with fertilizer contamination)Â
Mechanism
Rumen reduces nitrate to nitrite. Nitrite reduces the iron in heme forming methemoglobin that can’t carry oxygen – the affected animal become anoxic. Clinical signs will occur at 30-40% methemoglobin, death can occur when methemoglobin is >70%.
Signs
Rapid onset (30 minutes to hours) of weakness, bloat, ataxia, recumbency, cyanosis, and death. The rapid progression from consumption to death precludes the formation of any reliable lesions. Pregnant animals that survive the acute disease may abort 3-7 days after exposure.
Treatment
Methylene blue is the traditional antidote administered at 10 mg/kg of a 1% solution. There are withdrawal concerns for the use of methylene blue due to it being a potential carcinogen, FARAD should be consulted. Remove the suspect source.
Diagnosis
Brown discoloration of venous blood. Serum is a good antemortem sample, ocular fluid is the best post-mortem sample. Rumen content is not a good post-mortem sample as the rumen microbes will continue to degrade nitrate. Methemoglobin rapidly decays after collection so its diagnostic utility is limited.Â
1% nitrate in forage can result in acute deaths, 0.5% nitrate feed should not be fed to pregnant animals. 100 ppm in water can result in clinical signs. Laboratories that do feed and water analyses use different units to report the nitrate content, these units are different and it is imperative to recognize the differences.
