Japanese yew intoxication in a herd of cattle

Dominque Comeau 

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2023;27(4):10.

In a herd of ten Shorthorn cattle, there were three sudden deaths within 12 hours.  Two of the affected animals were 4-year-old cows, one of whom had calved in the previous month.  The third animal was a 4-year-old bull.  All animals showed no preceding clinical signs, were noted to have no lameness or abnormal behavior prior to death, and were seen eating well and chewing cud just before being found dead.  They had been in the same field for one month.  The field was walked, and no debris or material of concern was noted at that time.  The most recent sudden death was submitted to the Animal Health Laboratory for postmortem examination.

On external examination, there were external injuries consistent with scavenging; the wounds were postmortem and considered unrelated to the cause of death.  The rumen was filled with abundant moist green fibrous digesta.  There were scattered twigs, as well as multiple symmetrical elongated flat leaves with a defined, slightly curved point at the tip.  These were determined to be leaves from the Japanese yew plant (Figs. 1, 2).  There were also fragments of woody stems and rare small red-brown berries/seeds in the rumen.  

Japanese yew is an ornamental shrub that grows well in colder climates, and thus is very common in Canada and the northern United States.  All parts of the leaves and seeds are highly toxic to cattle, as well as other grazing animals such as goats, sheep, and horses.  Exposure is most often due to grazing in areas where the shrubs grow, or by feeding landscaping trimmings to livestock.  The plant is toxic year-round, and maintains its toxicity when dried.  It contains alkaloids called taxines which are highly cardiotoxic; they act as cardio-depressants by inhibiting sodium and calcium conduction within the muscles of the heart, leading to diastolic cardiac arrest.  Exposure to even a small amount of the plant is dangerous, as ingestion of only 1-10 grams per kilogram body weight is sufficient to cause fatal toxicity.  The toxins are rapidly metabolized and cannot be analyzed in tissue or digesta, and intoxication causes no specific gross lesions.  Diagnosis depends on the identification of the plant material in the mouth, esophagus, or forestomaches.

Following identification of the plant in this case, it was confirmed that the owner had cut the shrubs around his home and thrown the trimmings into the pasture with the cattle.  This case highlights the importance of careful monitoring of feed/plants/water that livestock have access to, and of considering all potential sources of exposure in cases of suspected toxicity.  The latter is especially relevant in this case, as the trimming pile was not considered in the initial walkthrough of the field, and was not included in the original history.  The cattle were removed from the pasture and no further losses were reported.

Figure 1. A selection of the leaves, seeds, and stems from the rumen of the affected cow.

Figure 2. Reference photo for the appearance of Japanese yew.

http://www.bio.brandeis.edu/fieldbio/pkenlan/HTML/Taxaceae/taxus_cuspidata.html

References

1. Wilson CR, et al. Taxines: A review of the mechanism and toxicity of yew (Taxus spp.) alkaloids. Toxicon 2001;39 (2-3):175-185.  

2. Sula JM et al. Characterization of cardiac lesions in calves after ingestion of Japanese Yew (Taxus cuspidata). J Vet Diagn Invest 2013;25(4):522-26.