WSU College of Veterinary Medicine senior paper highlights, July 2024
By Rachel Wurzel (Advisor: Dr. John Wenz)
Summary: While seeing cattle out on rangeland may stir feelings of nostalgia for traditional ranching and the feeling that all is right in the world, its appearance of simplicity can be deceiving. Rangeland cattle management has its own set of unique challenges, including the array of plants on which cattle graze. If the availability of the forage that is favored by cattle decreases, cattle will consume plants that are not as palatable, some of which have toxic properties. Toxicities resulting from such plants will be discussed, specifically nitrate, pyrrolizidine alkaloid, and quinolizidine alkaloid. This overview includes identification of the toxic plant, a description of the most at risk groups, and an explanation of the pathophysiology that results in the common presenting clinical signs. This review will investigate the treatment options for clinical animals and the preventive measures for subclinical incidences within a herd. Ranchers can avoid the toxic effects associated with ingestion of these plants by providing sufficient forage for animals on the range, however the determination of adequate forage is specific to the animal and the land on which its grazing. This paper provides a research-based guide to providing suitable grazing for rangeland cattle. Providing adequate forage, implementing pasture management practices, and frequently monitoring grazing cattle is crucial to preventing nitrate and alkaloid toxicosis.
Conclusions: A large sector of the beef industry, cow calf operations that use pasture and rangeland to feed their herds. Alkaloids are found in many plants that grow within pastures. Quinolizidine alkaloids found in lupine plants ingested by cattle during days 40-120 of gestation are responsible for causing crooked calf syndrome. This is classified by skeletal deformities due to anagyrine’s blocking effect of skeletal muscle nicotinic acetylcholine receptors. Pyrrolizidine alkaloids found in Senecio spp, Cynoglossum officinale, and Heliotropium are metabolized into toxic pyrroles that lead to liver damage. This liver damage may not manifest at the time of ingestion, but it can lead to clinical signs or death during times of immense stress.
Another toxicity is found in pasture crops and weeds on rangeland, in plants that accumulate nitrate. Nitrates are converted into proteins within the plant through photosynthesis, but under specific conditions, this system is overwhelmed. When the cow eats this forage, the nitrate is reduced to nitrite and ammonia in the rumen. The rumen microbes then convert ammonia into protein. If this system is flooded by an increased number of nitrates, nitrite accumulates in the blood, pairing with ferrous iron to create intravascular methemoglobin. Methemoglobinemia results in anemic anoxia leading to clinical signs of dyspnea, tachycardia, ataxia, weakness, and death. Diagnosis is based on chemical analysis of forage samples, antemortem blood samples, and postmortem enucleation being sent in for analysis. Treatment includes immediate removal from suspected forages, offering high carbohydrate feed options, and administering intravenous methylene blue.
Providing adequate forage is a crucial factor in preventing cattle from grazing toxic plants. Determining adequate forage can be challenging, as it is often specific to a rancher’s situation. A representative sample can be acquired by snipping thirty to fifty samples of the forage being eaten, at least 400 grams, and sending it in for analysis. When interpreting the analysis, a special emphasis is placed on crude protein, total digestible nutrients, and dry matter digestibility. These values should be interpreted in light of the energy, protein, mineral, vitamin, and water requirements of cattle.
By Lainee Colombik (Advisor: Dr. Dr. Chrissy Eckstrand)
Summary: Porcine respiratory and reproductive syndrome (PRRS) is one of the most significant diseases affecting the pork industry in the United States and worldwide. The virus is a single-stranded, RNA virus that has an initial tropism for alveolar macrophages and spreads to affect more distant lymphatic tissues. Clinical signs associated with the disease include both respiratory tract signs and substantial reproductive failure. The virus is readily spread through aerosols, fomites, and direct contact between individuals. Currently there is no effective treatment for PRRSV infection.
Implementing strategies to prevent viral introduction into naïve herds is economically more manageable than trying to eliminate PRRSV from a positive herd. Biosecurity protocols that are effective at preventing viral introduction are dynamic and cover the many ways the virus can enter the operation. The primary areas of concern are personnel coming and going, transportation vehicles, movement of pigs through the operation, and aerosol spread in pig dense regions. Vaccination is a widely used method to stabilize positive herds, however results are unpredictable and reproductive losses are still seen. Herd closure and exposure, test and removal, and whole herd depopulation are all methods used to return herds to a PRRSV negative status. Finally, gene edited PRRS resistant herds are being developed and may soon be approved for human consumption.
This disease is both widespread and significant in domestic swine populations. Veterinarians have a responsibility to understand this disease and to work towards decreasing the associated losses. The following paper is a review of current available literature surrounding PRRS.
Conclusions: Porcine respiratory and reproductive syndrome virus is a single-stranded RNA virus that is actively infecting many herds across the United States. The virus has an initial tropism for alveolar macrophages and spreads to other lymphatic tissues as the disease progresses. Clinical signs associated with infections include decreased reproductive performance and those associated with respiratory tract infection. Some individuals clear the infections rapidly while others remain persistently infected and shed the virus for 200 days or longer.
There are several diagnostics available for identifying PRRSV infections. The most common diagnostic used is the Idexx HerdChek 3x ELISA. This assay detects serum antibodies against the PRRS virus but does not differentiate between vaccinated and infected animals. IFA and SVN are other serological diagnostics; however, they are less reliable. RT-PCR is more expensive and takes more time but is a diagnostic that can differentiate wild-type infection and vaccination. Currently, there are no diagnostics available for differentiating persistently infected animals and those that were infected and have since cleared the virus.
PRRSV is shed in the milk, saliva, urine, colostrum, semen, and feces of infected animals and can also be spread via contact with whole blood. Viral persistence in the environment is prolonged in cool and moist environments. The virus is inactivated by iodine, chlorine, quaternary ammonium compounds, and UV light.
Maintaining a PRRSV negative herd is labor intensive and requires strict biosecurity protocols that address the vast number of routes in which the virus can enter an operation; however, the alternative is managing a positive herd. When managing positive herds, producers can either work to eliminate the virus or stabilize their herd in the face of the virus. To stabilize a herd, many operations choose to vaccinate their breeding stock. To eliminate the virus the options are herd closure and exposure, test and removal or whole herd depopulation. These options can be labor intensive, time consuming, and economically non-feasible.
New research has uncovered the genetic marker associated with PRRSV resistance. Utilizing CRISPR/CAS9, a small population of pigs that are PRRSV resistant have been developed. These pigs are intended to be used for commercial distribution and worldwide consumption, pending approval from the United States Food and Drug Administration. This modern technology shows promise for reducing the economic pressure of the PRRS disease; however, there will be hurdles pushing this technology into the food chain.
The purpose of this paper was to give an overview of the characteristics of a current management practice associated with porcine respiratory and reproductive syndrome virus. PRRSV is affecting swine herds across the United States and contributing to major economic losses in the pork industry. There is a responsibility for swine veterinarians to understand how to recognize and manage this disease at the herd level and in outbreak situations.
By Neils Stegelmeier (Advisor: Dr. McConnel)
Summary: Bovine Respiratory Disease is one of the leading causes of preweaning mortality in dairy calves. Difficulties in managing BRD include diagnosing affected calves. This results in increased morbidity and mortality. Transcriptomic analysis of leukocytes has been utilized to identify genes of disease resiliency. This study followed two cohorts of 30 calves for 11 weeks on two dairies. Blood samples, clinical assessments, and thoracic ultrasonography were used to categorize calves into heathy, clinical respiratory signs (CRSC+), and consolidated lung lobes (TUS+). Subgroups were created if calves recovered or remained consolidated (chronic). Peripheral leukocytes were extracted using a ficoll-paque separation and analyzed by Novogene Corporation. Transcriptome analysis was conducted via the GEMmaker workflow, and a gene expression matrix was created. Raw sample reads were mapped to the Bos taurus reference genome, analyzed using the Bioconductor packages, and a list of differentially expressed genes was analyzed with g:Profiler functional enrichment. TUS+ calves demonstrated an up-regulation of genes of inflammation and a down-regulation of genes indicating host-pathogen interactions (immune suppression). CRSC+ calves demonstrated an up-regulation of genes involved in active immune response to viral pathogens and a down-regulation of cell-division machinery (redirected resources from growth to defense). Chronically consolidated calves had up-regulated mRNA synthesis and stability and down-regulation of components involved in gas transport (pathogen mediated due to decreased gas exchange). These comparisons indicate that transcriptomic analysis and DGE may identify biomarkers for disease status in calves that may help guide future diagnostic insight into disease severity and duration.
Conclusions: The functional analysis of upregulated and downregulated genes correlates with clinical findings of calves and the pathophysiologic understanding of BRD. This suggests that DGE could be utilized to identify health categories. Transcriptomics could provide insights into disease states and recovery (resilience = resistance + tolerance). Research is ongoing to identify traits of resiliency, and long-term impacts of respiratory disease in dairy calves.