Don't Let Your Cattle Fall Victim to Toxins

An Inside Look of Toxicology Cases at Kansas State University's Veterinary Diagnostic Lab

By Scott Fritz, DVM, DABVT, Kansas State Veterinary Diagnostic Laboratory

Looking back at 2023, our industry faced many challenges in different parts of the country. Generational drought ravaged many areas, leading to smaller animal inventories and record-breaking prices. Along with that came increased input costs driving many producers to utilize unconventional feedstuffs and management practices to try and weather the storm. As a diagnostician, many of the health challenges we face seem to stem from practices that deviate from “normal” and last year was no exception. The intent of the following article is to summarize some of the trends we have experienced at the Kansas State Veterinary Diagnostic Laboratory, specifically focusing on toxicology cases. For readers that are unaware, the toxicology section at KSVDL was initiated in 2018 and has since grown annually in tests offered and performed. We are one of the only toxicology sections in the country with a special interest in production animals and our case submissions are approximately 80% cattle.

Most toxicology cases in cattle are related to exposures in feed or water – many are simply an over-accumulation of compounds normally present in forages. These over-accumulations often result from adverse growing conditions of our forage crops and drought is the most significant. Occasional issues with mis-formulations, mistakes in milling, worn-out equipment, and unintended inclusion can result in significant health effects as we typically performing photosynthesis. Excessive nitrate intake in ruminants eventually results in the inability of the blood to distribute oxygen to tissues in the body. Animals look inebriated and will fall down and eventually die. An often-overlooked source of nitrate for animals is water. We experience several cases annually where a producer is forced to haul water for livestock use. Many producers have plastic fertilizer tanks already attached to trailers are feeding production animals in a group setting, meaning lots of animals are exposed at a time. Water quality changes can result from drought and are often overlooked as contributing to dietary intake. Water quantity also becomes a concern in many areas and hauling water for livestock use is a common history in some cases where producers experience significant animal loss in a very short period of time.

One of the most common diagnoses in death loss events is nitrate poisoning. Many producers are aware of nitrate potential in drought stressed forages and row crops. Sorghum/sudan, Johnsongrass, and corn are common sources of excess nitrate, and the accumulation is a result of the stressed plants not and it is very convenient to fill these tanks with water and haul them down the road. The problem is the fertilizers are very concentrated in relation to excessive water concentrations. For reference, a 40% nitrogen fertilizer is equivalent to 400,000 ppm, while 100 ppm nitrate in water can cause significant health issues in cattle. Even when these tanks are washed, they have been responsible for excessive exposure. Some fertilizer formulations use urea as a nitrogen source and overconsumption of urea can cause another problem altogether. Ruminants have an enzyme in their rumen called urease which degrades urea to ammonium and ammonia. In cases where animals consume too much, they are unable to excrete ammonia fast enough and end up with too much ammonia in their blood, which causes neurologic signs and rapid death. We can detect both ammonia and nitrate in ocular fluid of a deceased animal and many times in these cases using fertilizer tanks, both are elevated. Producers are encouraged to have dedicated water-hauling equipment in order to avoid these issues.

Another common neurologic syndrome is a disease known as polioencephalomalacia or “polio” for short. Clinically this disease is characterized by blindness, head-pressing, tremors, and seizures. The disease has traditionally been blamed on a dietary thiamine deficiency but recently has been shown to be the result of elevated dietary sulfur concentrations. Common sources of sulfur include water in many areas of the country, some ethanol co-products, and some forage plants. It is important to consider both the diet and the water when evaluating total sulfur intake, as animals consuming high-sulfate water cannot tolerate as much sulfur in the diet. Some other co-products have also been responsible for contributing to dietary sulfur, the most significant case last year involved poultry litter. In lieu of listing all of the suspect materials, it is important to realize that co-products do not have oversight on their formulation, therefore it is best to assume each load is different than the one before and we would be wise to do some basic nutritional analysis prior to inclusion in animal rations.

Ionophore antibiotics are widely used safely to increase rate of gain and feed efficiency in ruminants. Because these products are so widely used, we invariably have problems with the actual dose that ends up in rations. All it takes is a onetime mistake, such as missing a decimal point or adding a wrong product into a batch of feed, to cause significant health challenges. Ionophore toxicosis can be a difficult diagnosis as there is a delay from ingestion to clinical effects. This delay is often 48 hours or longer and death loss typically peaks around a week post-exposure. This means that the offending feed has already been consumed and does not exist anymore unless batch samples are retained. Ionophore poisoning is often diagnosed using microscopic evaluation of the heart and other muscles. These compounds in an overdose situation affect the ability of cells to make energy and hi-energy tissues like muscle are the first affected. In many cases there are animals that succumb to the overdose initially, but other sub-lethally exposed animals will experience significant impacts on growth and rate of gain, and some may succumb to heart failure months after the initial exposure. These cases can be challenging to work up and can last for months. It is a good practice to have open communication between the producer, veterinarian, and diagnostic laboratory.

Drought obviously affects the amount of forage produced which affects intake. One overlooked secondary effect of reduced feed intake is reduced mineral intake. Many loose mineral products are formulated based upon dry-matter intake which drives the daily intake of supplements. When animals do not consume the mineral supplement as readily as the product intends, mineral deficiencies can occur. Copper deficiency is the most common abnormality we see in beef cattle. Minerals in general are transferred across the placenta during the last trimester of pregnancy and calves are born with what they need to last for about the first six months of life, until they start to consume an oral supplement themselves. It should follow that calves born to copper-deficient cows may not have adequate stores to get them through. In many cases of pre-weaning respiratory disease in pasture settings, calves are copper deficient. The same holds true for many significant outbreaks of respiratory disease at weaning or when placed in yards. Copper is involved in many enzymes and processes in the immune response and often contributes to these outbreaks. Producers should consider the potential for mineral deficiencies in a drought year and adjust the mineral program as needed. Liver biopsies are commonly performed to measure the mineral concentrations in cows and calves as the liver is the storage organ for many minerals. This can be performed by your local veterinarian and submitted to KSVDL for analysis.

2023 was the year of abnormal sources for many of the compounds we normally deal with. It is important to work with your local veterinarian as they are the most in tune with local growth conditions and forage issues in your area.

Dr. Scott Fritz earned his DVM from Iowa State University in 2014. He then spent 5 years in private practice in rural South Dakota focusing on beef cattle. In 2019 Dr. Fritz started a residency in toxicology at the Kansas State Veterinary Diagnostic Laboratory with a focus on diagnostic medicine. He is board-certified by the American Board of Veterinary Toxicology and currently serves as a diagnostician and faculty member at the Kansas State University College of Veterinary Medicine.