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Proceeding Paper

Diseases in Ruminants Associated with Pteridium aquilinum Ingestion †

Exotic and Wildlife Service, Veterinary Teaching Hospital, University of Trás-os-Montes and Alto Douro, 5000-801 Vila Real, Portugal
CECAV, University of Trás-os-Montes and Alto Douro, 5000-801 Vila Real, Portugal
CITAB, University of Trás-os-Montes and Alto Douro, 5000-801 Vila Real, Portugal
Direção Geral de Alimentação e Veterinária, Campo Grande, 50, 1700-093 Lisboa, Portugal
Author to whom correspondence should be addressed.
Presented at the 2nd International Electronic Conference on Toxins, 14–28 July 2023; Available online:
Biol. Life Sci. Forum 2023, 24(1), 8;
Published: 27 September 2023
(This article belongs to the Proceedings of The 2nd International Electronic Conference on Toxins)


Pteridium aquilinum (L.) Kuhn, commonly known as bracken fern, is a cosmopolitan plant species absent only from polar and desert regions. Worldwide, Pteridium aquilinum has been rapidly spreading due to the neglect of agricultural fields and the growing wave of forest fires. This plant has several toxic components such as thiaminases, brains, active glucosides, beta-glucopyranosides and ptaquloside in its constitution that can be lethal to animals. The animals do not normally choose it as food, except in situations of food shortage, in periods of drought, when the ferns are still green or when the animals graze in places with large amounts of the plant in question. In order to revisit the major syndromes caused by P. aquilinum’s major toxins, the authors present several cases of acute and chronic ruminant poisoning associated with ingesting P. aquilinum in Portugal in sheep and cattle. The primary associated syndromes observed in animals that consume this plant were thiamine deficiency, blindness in sheep, acute or subacute poisoning with bone marrow depression, and consequently, leucopenia and bladder tumors in cattle. Given the economic impact of the diseases caused by the toxins of this plant, and the possible public health implications, it is imperative to minimize these syndromes in animals and establish measures for their prevention.

1. Introduction

Pteridium aquilinum (L.) Kuhn, commonly referred as the common fern, fento or fern of the mountains, or female fern of apothecary, is a cosmopolitan species, absent only in the polar and desert regions (Figure 1) [1,2,3].
There are two subspecies and, within these, several geographical races. Tyron, quoted by Page, 1976, distinguishes subspecies Aquilinum and Caudatum, each with different varieties [4].
The global presence of Pteridium aquilinum can be attributed to its remarkable adaptability to various environmental conditions. This plant exhibits a highly opportunistic nature and employs a range of mechanisms to sustain its dominance. One such mechanism involves the synthesis of substances that, upon release into the environment or incorporation into the soil following the fern’s demise, effectively hinder the emergence and growth of other plants. This attribute grants P. aquilinum allelopathic characteristics. Additionally, the fern employs the production of several secondary metabolites as a survival strategy, serving as deterrents for potential predators [1,5,6].
The morphology of this plant can be categorized into three main parts, roots, rhizomes and fronds, with the fronds featuring fiddleheads in their immature stage (Figure 2). As the bracken fern (BF) develops, the fiddlehead progressively unfurls, eventually giving rise to mature fronds responsible for the dispersal of essential spores required for reproduction [7,8].
In order to revisit the major syndromes caused by P. aquilinum major toxins, the authors present several cases of acute and chronic ruminant poisoning associated with ingesting P. aquilinum in Portugal in sheep and cattle.

2. Material and Methods

Based on the cases received at the Histology and Anatomical Pathology and at the Veterinary Hospital of UTAD (Vila Real, Portugal), the authors describe the main animal syndromes associated with the ingestion of P. aquilinum in ruminants, based on the literature.

3. Results and Discussion

The primary associated syndromes observed in animals that consume this plant were thiamine deficiency, blindness in sheep, acute or subacute poisoning with bone marrow depression, and consequently, leucopenia and bladder tumors in cattle.
The plant in question possesses various toxic constituents, namely illudane and illudalane sesquiterpenes, nor-sesquiterpenes, benzoic acid derivatives, cinnamic acid derivatives, enzymes and thiaminases, which contribute to thiamine (vitamin B1) deficiency, particularly in equines. Also, it contains flavonoid antioxidants such as quercetin and kaempferol, along with an unstable glycoside. Notably, the plant harbors a prominent carcinogenic compound known as ptaquiloside, which is primarily responsible for its carcinogenic properties [9,10,11,12].

3.1. Thiamine Deficiency

Thiamine deficiencies are frequent, due to the type 1 thiaminase present in this plant. They mainly affect monogastric herbivores such as horses since the microbial flora can synthesize this vitamin from its derivatives in ruminants [13,14,15]. Typical cases of poisoning from bracken fern require relatively high doses over an extended period, such as consuming hay contaminated with 20–25% bracken fern for at least three months or longer. In horses, the condition known as equine bracken staggers is characterized by symptoms including anorexia, weight loss, lack of coordination, a hunched posture with an arched back and neck, and a wide stance with feet apart. Trembling muscles can be observed when the affected horses are forced to move. In severe cases, tachycardia and arrhythmias may occur, and death usually follows within 2–10 days after the onset of symptoms. Prior to death, convulsions, clonic spasms and opisthotonos may be observed. The poisoning has been linked to bracken fern thiaminases, as the clinical manifestations resemble those of a vitamin B1 deficiency. Thiamine therapy is commonly employed, and most animals respond well to it [16,17,18].
Poisoning in pigs is relatively rare and presents with less distinct symptoms. Affected pigs typically exhibit anorexia and weight loss. In the terminal phase, the condition may resemble heart failure, and sudden death can occur following recumbency (lying down) and difficulty breathing (dyspnea). However, in sheep fed P. aquilinum together with other thiaminase-rich plants, polioencephalomalacia associated with thiamine deficiency has been diagnosed [13,14,15].

3.2. Blindness in Sheep

In sheep, ingestion of Pteridium aquilinum appears to be associated with blindness due to progressive retinal atrophy (Figure 3) [19].
The condition known as tapel hyperreflectivity is clinically recognized. These affected animals experience permanent blindness and remain generally alert. The responsiveness of their pupils to light is typically diminished, and advanced cases display narrowed arteries and veins during funduscopic examination. Moreover, the tapetum nigrum, a layer of the eye responsible for reflecting light, appears pale with fine cracks and gray spots. Histologically, the affected animals exhibit a severe degeneration of retinal rods, cones and the outer nuclear layer, which is most prominent in the tapetal portion of the retina [16,17,20]. Additionally, these animals often present with various other lesions associated with bracken fern consumption, including bone marrow suppression, hemorrhage, immunosuppression and urinary tract neoplasia [21].

3.3. Acute or Subacute Poisoning

Ingestion of bracken fern can lead to acute poisoning and produce various clinical symptoms, including fever, apathy, drooling and hemorrhages in organs such as the gums, nostrils and gastrointestinal tract. Hematuria and blood in the milk may also occur. Necropsy findings often include red infarcts in the liver and significant bone marrow aplasia [12,22,23,24].

3.4. Bladder Tumors in Cattle

Associated with fetus carcinogens are bladder neoplasms (Figure 4), usually with enzootic hematuria and upper alimentary tract neoplasms in cattle [19].
The major carcinogenic compound of Pteridium is known as ptaquiloside [9,10,11,12,25,26,27].
Ptaquiloside contains the potent carcinogen dienone 2. Studies have revealed that under weak alkaline conditions, dienone 2 exhibits significant alkylating activity, leading to the cleavage of deoxyribonucleic acid (DNA). Consumption of bracken fern in high doses can cause DNA damage, resulting in programmed cell death and cell cycle arrest even at lower doses [12,28].
PTA shows lower levels in roots and spores but higher concentrations in edible parts and crosiers [29]. Fortunately, hydrothermal methods have been discovered to degrade PTA into a stable form, potentially reducing its toxicity. However, there is a need for further research to provide specific information and evidence on the reduction of its toxicity, such as conducting in vitro cytotoxicity tests, and to determine the optimal conditions for PTA degradation, including the temperature and heating duration [7,30].

4. Conclusions

Pteridium aquilinum, commonly known as bracken fern, has rapidly expanded its global presence, particularly in Portugal, where it poses a significant potential threat due to favorable environmental conditions. The spread of P. aquilinum has been facilitated by the abandonment of certain agricultural crops and the increasing occurrence of forest fires. This fern species has an extensive rhizome system that allows it to survive fires, and while it does not produce spores in shaded areas, exposed regions promote the development of sporangia, leading to the production of a large number of spores. These spores, characterized by their small size, are easily dispersed by the wind. Furthermore, P. aquilinum is one of the first plants to colonize newly burned areas.
Bracken fern intoxication is incurable, except in cases of thiamin deficiency. Therefore, it is crucial to control and prevent exposure to this plant. Implementing improved grazing management and alternating grazing between fern-contaminated and fern-free areas at three-week intervals can help minimize the risk of poisoning. Measures to stop the growth and density of bracken fern are important and could include regular cutting of mature plants or, if suitable, deep tillage.
Climate change appears to have a favorable impact on the spread of bracken fern, particularly in Northern Europe and mountainous regions. Rising temperatures, extended growing seasons, increased humidity and additional hours of sunlight contribute to its proliferation. However, it is important to recognize the negative consequences that this fern can bring to both humans and animals. Therefore, caution must be exercised to prevent excessive exposure to its hazardous chemicals.

Author Contributions

Conceptualization, F.S. and I.P.; methodology, F.S. and I.P.; software, F.S., A.G., C.M. and I.P.; validation F.S., A.G., C.M. and I.P.; formal analysis, F.S., A.G., C.M. and I.P.; investigation, C.M. and I.P.; resources, A.G. and I.P.; data curation, A.G. and I.P.; writing—original draft preparation, C.M. and I.P.; writing—review and editing, F.S., A.G., C.M. and I.P.; visualization, F.S., A.G., C.M. and I.P.; supervision, I.P.; project administration, I.P.; and funding acquisition, I.P. and F.S. All authors have read and agreed to the published version of the manuscript.


The participation of Pires I, Silva F. was supported by the projects UIDB/CVT/00772/2020 and LA/P/0059/2020, funded by the Portuguese Foundation for Science and Technology (FCT). (Project UIDB/CVT/0772/2020). The participation of Garcês A. was supported by National Funds from FCT Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.


  1. Fernandes, A.; Betarda, R. Iconographia Selecta Florae Azoricae; Secretaria Regional da Cultura Autonoma dos Açores: Açores, Portugal, 1980.
  2. Rivera Núñez, D. La guía de Incafo de las Plantas útiles y Venenosas de la Península Ibérica y Baleares (Excluídas Medicinales); Las guías verdes; Incado: Madrid, Spain, 1991; ISBN 978-84-85389-83-4. [Google Scholar]
  3. Durão, J.; Ferreira, M.; Cabral, A.; Peleteiro, M.C.; Afonso, F.; Correia, J. Aspectos Anatomopatológicos e Clínicos Da Hematúria Enzoótica Dos Bovinos. Rev. Port. De Ciências Veterinárias 1995, 90, 132–136. [Google Scholar]
  4. Page, C.N. The Taxonomy and Phytogeography of Bracken—A Review. Bot. J. Linn. Soc. 1976, 73, 1–34. [Google Scholar] [CrossRef]
  5. Cooper-Driver, G. Chemotaxonomy and Phytochemical Ecology of Bracken. Bot. J. Linn. Soc. 1976, 73, 35–46. [Google Scholar] [CrossRef]
  6. Gliessman, S.R. Allelopathy in a Broad Spectrum of Environments as Illustrated by Bracken. Bot. J. Linn. Soc. 1976, 73, 95–104. [Google Scholar] [CrossRef]
  7. Kim, M.K.; Kang, J.S.; Kundu, A.; Kim, H.S.; Lee, B.-M. Risk Assessment and Risk Reduction of Ptaquiloside in Bracken Fern. Toxics 2023, 11, 115. [Google Scholar] [CrossRef] [PubMed]
  8. Biological Flora of the British Isles: Pteridium aquilinum (L.) Kuhn. J. Ecol. 2006, MARRS, Wiley Online Library. Available online: (accessed on 31 May 2023).
  9. Soeder, R.W. Fern Constituents: Including Occurrence, Chemotaxonomy and Physiological Activity. Bot. Rev 1985, 51, 442–536. [Google Scholar] [CrossRef]
  10. Freitas, L.; Paranaíba, J.; Peréz, A.; Machado, M.; Lima, F. Toxicity of Pesticides in Lizards. Hum Exp Toxicol 2020, 39, 596–604. [Google Scholar] [CrossRef]
  11. Alonso, M.B.; Feo, M.L.; Corcellas, C.; Vidal, L.G.; Bertozzi, C.P.; Marigo, J.; Secchi, E.R.; Bassoi, M.; Azevedo, A.F.; Dorneles, P.R.; et al. Pyrethroids: A New Threat to Marine Mammals? Environ. Int. 2012, 47, 99–106. [Google Scholar] [CrossRef]
  12. Ugochukwu, I.C.I. Bracken Fern Toxicity and Its Associated Clinicopathological Effects in Humans and Animals: A Review. Comp. Clin. Pathol. 2019, 28, 593–597. [Google Scholar] [CrossRef]
  13. Evans, W.C. Bracken Thiaminase-Mediated Neurotoxic Syndromes. Bot. J. Linn. Soc. 1976, 73, 113–131. [Google Scholar] [CrossRef]
  14. Bakker, H.J.; Dickson, J.; Steele, P.; Nottle, M.C. Experimental Induction of Ovine Polioencephalomalacia. Vet. Rec. 1980, 107, 464–466. [Google Scholar] [CrossRef]
  15. Chick, B.F.; Carroll, S.N.; Kennedy, C.; McCleary, B.V. Some Biochemical Features of an Outbreak of Polioencephalomalacia in Sheep. Aust. Vet. J. 1981, 57, 251–252. [Google Scholar] [CrossRef]
  16. Plumlee, K.H. Clinical Veterinary Toxicology; Mosby: St. Louis, MO, USA, 2004; ISSN 9780323-011259. [Google Scholar]
  17. Fenwick, G.R. Bracken (Pteridium Aquilinum)—Toxic Effects and Toxic Constituents. J. Sci. Food Agric. 1989, 46, 147–173. [Google Scholar] [CrossRef]
  18. Caloni, F.; Cortinovis, C. Plants Poisonous to Horses in Europe. Equine Vet. Educ. 2015, 27, 269–274. [Google Scholar] [CrossRef]
  19. Smith, B.L. Bracken Fern and Animal Health in Australia and New Zealand. AIAS Occas. Publ. 1990, 1, 227–232. [Google Scholar]
  20. Hirono, I.; Ito, M.; Yagyu, S.; Haga, M.; Wakamatsu, K.; Kishikawa, T.; Nishikawa, O.; Yamada, K.; Ojika, M.; Kigoshi, H. Reproduction of Progressive Retinal Degeneration (Bright Blindness) in Sheep by Administration of Ptaquiloside Contained in Bracken. J. Vet. Med. Sci. 1993, 55, 979–983. [Google Scholar] [CrossRef]
  21. Stegelmeier, B.L.; Field, R.; Panter, K.E.; Hall, J.O.; Welch, K.D.; Pfister, J.A.; Gardner, D.R.; Lee, S.T.; Colegate, S.; Davis, T.Z.; et al. Chapter 40—Selected Poisonous Plants Affecting Animal and Human Health. In Haschek and Rousseaux’s Handbook of Toxicologic Pathology, 3rd ed.; Haschek, W.M., Rousseaux, C.G., Wallig, M.A., Eds.; Academic Press: Boston, MA, USA, 2013; pp. 1259–1314. ISBN 978-0-12-415759-0. [Google Scholar]
  22. Kigoshi, H.; Niwa, M.; Ohashi, H.; Tanaka, H.; Hirokawa, J.; Ishiwata, H.; Yamada, K. Synthesis of Bracken Ultimate Carcinogen Analogues Possessing a DNA Binding Moiety and Their DNA Cleaving Activities. Tetrahedron Lett. 1995, 36, 5349–5352. [Google Scholar] [CrossRef]
  23. Tourchi, M. Múltiples Efectos Del Helecho Macho En Condiciones in Vivo e in Vitro (En Inglés). Asian Pac. J. Cancer Prev. 2014, 15, 7507–7509. [Google Scholar]
  24. Anjos, B.L.; Irigoyen, L.F.; Fighera, R.A.; Gomes, A.D.; Kommers, G.D.; Barros, C.S.L. Intoxicação aguda por samambaia (Pteridium aquilinum) em bovinos na Região Central do Rio Grande do Sul. Pesq. Vet. Bras. 2008, 28, 501–507. [Google Scholar] [CrossRef]
  25. Gil da Costa, R.M.; Bastos, M.M.S.M.; Oliveira, P.A.; Lopes, C. Bracken-Associated Human and Animal Health Hazards: Chemical, Biological and Pathological Evidence. J. Hazard. Mater. 2012, 203–204, 1–12. [Google Scholar] [CrossRef]
  26. Pires, I.; Silva, F.; Queiroga, F.L.; Rodrigues, P.; Henriques, R.; Pinto, C.A.; Lopes, C. Epithelioid Hemangiosarcomas of the Bovine Urinary Bladder: A Histologic, Immunohistochemical, and Ultrastructural Examination of Four Tumors. J. Vet. Diagn. Investig. 2010, 22, 116–119. [Google Scholar] [CrossRef] [PubMed]
  27. Pires, I.; Magalhães, A.; Diez, J.; Saraiva, C.; Silva, F. Enzootic Bovine Hematuria; Academic Publications: Sofia, Bulgaria, 2020. [Google Scholar]
  28. Pires, I.; Queiroga, F.L.; Silva, F.; Pinto, C.; Lopes, C. Kaposi-like Vascular Tumor of the Urinary Bladder in a Cow. J. Vet. Med. Sci. 2009, 71, 831–833. [Google Scholar] [CrossRef] [PubMed]
  29. Sharma, R.; Bhat, T.K.; Sharma, O.P. The Environmental and Human Effects of Ptaquiloside-Induced Enzootic Bovine Hematuria: A Tumorous Disease of Cattle. Rev. Environ. Contam. Toxicol. 2013, 224, 53–95. [Google Scholar] [CrossRef] [PubMed]
  30. Chen, L.-Y.; Hu, A.; Chang, C.-J. The Degradation Mechanism of Toxic Atractyloside in Herbal Medicines by Decoction. Molecules 2013, 18, 2018–2028. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Geographical distribution of Pteridium aquilinum subspecies aquilinum (adapted from Page, 1976).
Figure 1. Geographical distribution of Pteridium aquilinum subspecies aquilinum (adapted from Page, 1976).
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Figure 2. Bracken fern (illustration by Andreia Garcês and photo by Isabel Pires).
Figure 2. Bracken fern (illustration by Andreia Garcês and photo by Isabel Pires).
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Figure 3. Sheep with blindness.
Figure 3. Sheep with blindness.
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Figure 4. Bladder tumor.
Figure 4. Bladder tumor.
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Silva, F.; Garcês, A.; Magalhães, C.; Pires, I. Diseases in Ruminants Associated with Pteridium aquilinum Ingestion. Biol. Life Sci. Forum 2023, 24, 8.

AMA Style

Silva F, Garcês A, Magalhães C, Pires I. Diseases in Ruminants Associated with Pteridium aquilinum Ingestion. Biology and Life Sciences Forum. 2023; 24(1):8.

Chicago/Turabian Style

Silva, Filipe, Andreia Garcês, Catarina Magalhães, and Isabel Pires. 2023. "Diseases in Ruminants Associated with Pteridium aquilinum Ingestion" Biology and Life Sciences Forum 24, no. 1: 8.

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