Biomarkers and their potential for detecting livestock plant poisonings in Western North America

The United States National Cancer Institute defines a biomarker as: "A biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease." In Veterinary Medicine, biomarkers associated with plant poisonings of livestock have great utility. Since grazing livestock poisoned by toxic plants are often found dead, biomarkers of plant poisoning allow for a more rapid postmortem diagnosis and response to prevent further deaths. The presence and concentration of toxins in poisonous plants are biomarkers of risk for livestock poisoning that can be measured by the chemical analysis of plant material. More difficult is, the detection of plant toxins or biomarkers in biological samples from intoxicated or deceased animals. The purpose of this article is to review potential biomarkers of plant poisoning in grazing livestock in the Western North America including recently investigated non-invasive sampling techniques. Plants discussed include larkspur, lupine, water hemlock, swainsonine-containing plants, selenium-containing plants, and pyrrolizidine alkaloid containing plants. Other factors such as animal age and sex that affect plant biomarker concentrations in vivo are also discussed.

Use of Herbarium Voucher Specimens To Investigate Phytochemical Composition in Poisonous Plant Research

Poisonous plants cause large losses to the livestock industry through death, reduced production efficiency, reproductive dysfunction, and compromised harvesting of rangeland and pasture forages. Research investigating poisonous plants is complex because there are hundreds of genera of toxic plants representing thousands of species. To investigate the effects of poisonous plants on livestock, a clear understanding of the taxonomic identity of the plant and the ability to collect the plant in sufficient quantities for scientific studies is required. Subsequently, the active principles must be defined and investigated in the taxa of interest to better predict risk and make recommendations to reduce losses. Herbaria are collections of preserved plant specimens and are an important resource in poisonous plant research. Voucher specimens have often been used in the identification of the plant for the experimental reproduction of suspected livestock poisoning associated with a spontaneous case. More recently, herbarium specimens have been used to investigate the chemical composition of toxic plants as well as the distribution of different chemotypes over the landscape. The primary purpose of this review is to highlight the chemical analysis of herbarium specimens in poisonous plant research.

Analysis of rumen contents and ocular fluid for toxic alkaloids from goats and cows dosed larkspur (Delphinium barbeyi), lupine (Lupinus leucophyllus), and death camas (Zigadenus paniculatus)

Larkspurs, lupines, and death camas can be acutely toxic to livestock and are serious poisonous plant problems in western North America. The toxicity of these plants depends on the composition and concentrations of the toxic alkaloids in the plants. In this study, goats and cows were dosed sub-lethal doses of larkspur, lupine, and death camas. Rumen contents and ocular fluid samples were collected, and simple extraction, sample preparation, and analytical methods were developed for the detection of toxic alkaloids in the rumen contents and ocular fluid samples. Toxic alkaloids were detected in the rumen contents and ocular fluid samples from the goats and cows dosed larkspur, lupine, and death camas. In addition, results from a case report where rumen contents were analyzed from a steer that was suspected to have died due to larkspur are reported. This demonstrates the utility of the methods described for the diagnosis of acute plant poisonings.

Animal and plant factors which affect larkspur toxicosis in cattle: Sex, age, breed, and plant chemotype

Larkspur (Delphinium spp.) poisoning is a long-term problem for cattle grazing on rangelands of western North America. Recent research has shown that both plant and animal-based factors are critical in understanding and mitigating larkspur poisoning in cattle. Non-toxicological factors including sex, age, cattle breed, and plant chemotype affect cattle responses to larkspur. For example, Angus heifers are more susceptible to larkspur intoxication than are steers or bulls. Young cattle appear to be more susceptible to larkspur poisoning than mature animals. Beef breeds of cattle are more susceptible to larkspur intoxication than dairy breeds. In addition to animal factors, plant alkaloid composition (chemotype) affects the potential toxicity for cattle because of differences in the ratios and concentrations of highly toxic N-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids compared to less lethal non-MSAL-type alkaloids. Animal- and plant-based factors can provide substantial information to inform livestock producers on management to reduce risk and cattle losses to various larkspur species in western North America.

The effect of alkaloid composition of larkspur (Delphinium) species on the intoxication of Angus heifers1

Cattle losses from larkspur (Delphinium spp.) toxicity are a long-term challenge on the rangelands of western North America. In addition to animal factors that affect livestock poisonings, plant alkaloid composition (chemotype) affects the intoxication of cattle because some chemotypes are significantly more toxic. Differences in larkspur chemotype toxicity are due to the ratios of N-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids to non-MSAL-type alkaloids and the concentrations of those alkaloids in the plant material. The objective of this study was to compare the responses of 6 Angus heifers to 6 chemotypes of larkspur using a Latin square study design. These Angus heifers from the USDA-ARS, Meat Animal Research Center in Clay Center, NE, were chosen for this research because they are the most larkspur-susceptible cattle observed to date. The 6 heifers were given an oral dose of dried ground larkspur and tested for muscle weakness with an exercise test (i.e., walk time). The 6 chemotypes of larkspur had non-MSAL to MSAL-type alkaloid ratios ranging from 1.4:1 to 6:1 and were administered at an oral dose of 7.5 mg/kg MSAL-type alkaloids BW. There was a treatment effect due to larkspur chemotype (P < 0.0001), and period effects were not significant (P = 0.6). There were also significant correlations between the length of time walking on a dirt track at 5 to 6 km/h, and total alkaloid dose (r = -0.92, P = 0.0045) and alkaloid ratio (r = -0.81, P = 0.0258). Serum alkaloid concentrations at 24 h after dosing were representative of the relative abundance of the alkaloid in the plant material. Results from this work suggest that total alkaloid concentrations in combination with alkaloid ratios can be used together to accurately predict the plant risk component of larkspur poisoning to grazing cattle. Animal factors such as cattle age, breed, and sex must also be considered to comprehensively manage larkspur risk.

Sex-dependent differences for larkspur (Delphinium barbeyi) toxicosis in yearling Angus cattle1

Larkspur (Delphinium spp.) poisoning is a long-term problem for cattle grazing on rangelands of western North America. Results from preliminary experiments have suggested that differences in larkspur toxicity may exist between heifers and bulls. The objective of this study was to compare the physiological responses of yearling Angus heifers, steers, and bulls with a standardized dose of Delphinium barbeyi and to test the hypothesis that the response is sex dependent. Clinical signs of intoxication, including muscle coordination and function, were measured 24 h after oral dosing with larkspur by walking the cattle at a pace of 5 to 6 km h-1 for up to 40 min on an oval dirt track. Due to the experimental methods used, the variation in susceptibility to larkspur was not quantifiable for walking times of 0 or 40 min or more. Larkspur susceptible animals that were not able to walk (0 min; 36% of the animals) or larkspur resistant animals that walked the entire test period of 40 min (9% of the animals) resulted in censored or truncated data. The statistical methods (censReg and lmec) were used to adjust for data truncation or censoring. The heifers were only able to walk -8.9 ± 3.9 min (65.5% censored on the left) compared with 13.2 ± 3.7 min for bulls and 15.9 ± 2.7 min for steers. When heifers were compared with bulls and steers together, heifers walked 23.4 ± 4.5 min less (P < 0.0001). Serum alkaloid concentrations were measured immediately before walking, and deltaline concentrations averaged 266 ± 28, 131 ± 20, and 219 ± 28 ng mL-1 for all heifers, steers, and bulls, respectively, and serum methyllycaconitine concentrations averaged 660 ± 46, 397 ± 32, and 612 ± 34 ng mL-1 for all heifers, steers, and bulls, respectively. The relative risk of a zero walk time for yearling heifers is 330% that of yearling bulls (P = 0.0008). These results suggest that yearling Angus heifers are more susceptible to larkspur intoxication and, when possible, heifers should be kept from grazing larkspur-infested rangelands as a simple management tool to reduce the risk of fatal poisoning.

Serum toxicokinetics after intravenous and oral dosing of larkspur toxins in goats

Poisoning of cattle by larkspur plants (Delphinium spp.) is a concern for cattle ranchers in western North America. Previous research studies have evaluated the toxicokinetic profile of multiple larkspur toxins in several livestock species. However, those studies were all performed by orally dosing plant material. Consequently some toxicokinetic parameters could not be definitively determined. In this study, we compared the serum toxicokinetic profile of the larkspur alkaloids methyllycaconitine (MLA) and deltaline in goats dosed both IV and via oral gavage. The results from this study indicate that the toxic alkaloids in larkspurs undergo flip-flop kinetics, meaning the rate of absorption of the alkaloids is slower than the rate of elimination. The implications of flip-flop kinetics in treating animals poisoned by larkspur is discussed.

The Effect of Co-Administration of Death Camas (Zigadenus spp.) and Low Larkspur (Delphinium spp.) in Cattle

In many rangeland settings, there is more than one potential poisonous plant. Two poisonous plants that are often found growing simultaneously in the same location in North American rangelands are death camas (Zigadenus spp.) and low larkspur (Delphinium spp.). The objective of this study was to determine if co-administration of death camas would exacerbate the toxicity of low larkspur in cattle. Cattle dosed with 2.0 g of death camas/kg BW showed slight frothing and lethargy, whereas cattle dosed with both death camas and low larkspur showed increased clinical signs of poisoning. Although qualitative differences in clinical signs of intoxication in cattle co-treated with death camas and low larkspur were observed, there were not any significant quantitative differences in heart rate or exercise-induced muscle fatigue. Co-treatment with death camas and low larkspur did not affect the serum zygacine kinetics, however, there was a difference in the larkspur alkaloid kinetics in the co-exposure group. Overall, the results from this study suggest that co-exposure to death camas and low larkspur is not significantly more toxic to cattle than exposure to the plants individually. The results from this study increase our knowledge and understanding regarding the acute toxicity of death camas and low larkspur in cattle.

Development of a PCR-Based Method for Detection of Delphinium Species in Poisoned Cattle

Toxic plants such as Delphinium spp. (i.e., larkspur) are a significant cause of livestock losses worldwide. Correctly determining the causative agent responsible for the death of an animal, whether by disease, poisonous plant, or other means, is critical in developing strategies to prevent future losses. The objective of this study was to develop an alternative diagnostic tool to microscopy and analytical chemistry to determine whether a particular poisonous plant was ingested. Polymerase chain reaction (PCR) is a tool that may allow detection of the genetic material from a specific plant within a complex matrix such as rumen contents. A pair of oligonucleotide primers specific to Delphinium spp. (i.e., larkspur) was developed; using these primers, a PCR product was detected in samples from an in vivo, in vitro, and in vivo/in vitro coupled digestion of Delphinium occidentale. Lastly, larkspur was detected in a matrix of ruminal material where the amount of larkspur was far less than what one would expect to find in the rumen contents of a poisoned animal. The PCR-based technique holds promise to diagnose larkspur and perhaps other toxic plant caused losses.

If one plant toxin is harmful to livestock, what about two?

When livestock are poisoned by plants in a range setting, there is normally more than one poisonous plant in that area. Additionally, many plants contain more than one compound that is toxic to livestock. Frequently, much is known regarding the toxicity of the individual plants and their individual toxins; however, little is known regarding the effect of coexposure to multiple toxic plants or even the effect of multiple toxins from an individual plant. This review discusses some basic principles of mixture toxicology with a focus on recent research that examined the effect of co-administering multiple plant toxins from the same plant and the effect of co-administration of two different poisonous plants, each with different types of toxins. As combined intoxications are likely common, this information will be useful in further developing management recommendations for ranchers and in designing additional experiments to study the toxicity of multiple poisonous plants to livestock.

Effect of α₇ nicotinic acetylcholine receptor agonists and antagonists on motor function in mice

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated cation channels found throughout the body, and serve to mediate diverse physiological functions. Muscle-type nAChRs located in the motor endplate region of muscle fibers play an integral role in muscle contraction and thus motor function. The toxicity and teratogenicity of many plants (which results in millions of dollars in losses annually to the livestock industry) are due to various toxins that bind to nAChRs including deltaline and methyllycaconitine (MLA) from larkspur (Delphinium) species, and nicotine and anabasine from tobacco (Nicotiana) species. The primary result of the actions of these alkaloids at nAChRs is neuromuscular paralysis and respiratory failure. The objective of this study was to further characterize the motor coordination deficiencies that occur upon exposure to a non-lethal dose of nAChR antagonists MLA and deltaline as well as nAChR agonists nicotine and anabasine. We evaluated the effect of nAChR agonists and antagonists on the motor function and coordination in mice using a balance beam, grip strength meter, rotarod, open field analysis and tremor monitor. These analyses demonstrated that within seconds after treatment the mice had significant loss of motor function and coordination that lasted up to 1 min, followed by a short period of quiescence. Recovery to normal muscle coordination was rapid, typically within approximately 10 min post-dosing. However, mice treated with the nAChR agonist nicotine and anabasine required a slightly longer time to recover some aspects of normal muscle function in comparison to mice treated with the nAChR antagonist MLA or deltaline.