Chapter 13 Toxicological disorders

Introduction

Illustrations of toxicological disorders in cattle present problems. The clinical signs may be transient, with death occurring within a few minutes, such as in yew (Taxus baccata) poisoning (p. 249). In many cases the signs may be nonspecific. Where the effects are confined largely to one system, the description has been given in the appropriate section, e.g., ergot and fescue foot are considered under locomotor disorders (7.158–7.160). In this chapter, toxicoses have been broadly grouped into plant, organic, and inorganic chemical sections, and a few examples are given of each group. They are taken from Brazil, China, Germany, New Zealand, South Africa, the UK, the USA, and Zimbabwe.

Food safety issues arising from residues of chemicals in meat, offal, and milk are extremely important. Farmers are obliged, under food safety regulations, to avoid contaminating the food chain and must withdraw produce contaminated with chemical residues from the food chain. Food businesses such as dairies and supermarkets will reject produce from farms with unresolved poisoning incidents.

Plant toxicoses

Bracken (bracken fern)

Definition

acute or chronic worldwide toxicity following ingestion of large quantities of bracken (bracken fern), which contains several bone marrow toxins (aplastic anemia factor) which kill precursor cells in the bone marrow.

Clinical features

bracken toxicosis is widespread in several continents. Bracken (Pteridium aquilinum) contains ptaquilosides and other compounds which act as a cumulative poison in two syndromes. Firstly, after ingesting large quantities for a few weeks, cattle may show an acute syndrome resulting from aplastic anemia and thrombocytopenia. Sudden death is occasionally seen. In 13.1 the vulva of the crossbred Angus cow is pale from severe anemia. The pinpoint hemorrhages result from thrombocytopenia. Hemorrhages elsewhere can cause epistaxis, hyphema (13.2) (bleeding into the anterior chamber), or hematuria from bladder mucosal hemorrhage (13.3).

13.1 Bracken poisoning: pale vulvar mucosa in cow (Angus cross)

13.2 Bracken poisoning: hemorrhages causing hyphema

13.3 Bracken poisoning: bladder mucosal hemorrhage

Secondly, long-term ingestion of considerable quantities of bracken for several months can lead to a chronic syndrome of enzootic hematuria. The ptaquilosides are carcinogens and cause bladder neoplasia, resulting in enzootic hematuria and malignancies such as hemangiosarcoma (13.4). Numerous discrete masses, seen protruding from the mucosal surface, bleed readily as the bladder distends and contracts. Some mucosal areas (top right, lower left) appear normal. The hemangiomata can develop into ulcerating tumors of various types. Alimentary tract neoplasms include squamous cell carcinomas and papillomas affecting the pharynx and esophagus, respectively. 13.5 shows pharyngeal squamous cell carcinomas (A) and esophageal papillomas (B) identified in Brazil. Bovine papillomavirus (types 2 and 4) may also be involved in upper alimentary neoplasms.

13.4 Bracken poisoning: several hemangiosarcomata protruding from bladder mucosa

13.5 Bracken poisoning: alimentary tract neoplasis: (A) pharyngeal squamous cell carcinomas, (B) esophageal papillomas (Brazil)

Differential diagnosis

acute syndrome: anthrax (12.63), septicemic pasteurellosis (5.10), PPH syndrome (9.39), mycotoxicosis (p. 253); chronic cases: pyelonephritis (10.1, 10.2), cystitis, babesiosis (12.41).

Diagnosis

a history of exposure to bracken, clinical signs of severe anemia and pancytopenia, and low platelet counts. Most outbreaks in grazing cattle have many subclinically affected animals with markedly abnormal blood parameters.

Management

treatment of individual cases is usually hopeless, possibly blood transfusion (5–10 liters); pasture and grazing management (bracken eradication). Food safety implications, resulting from the excretion of bone marrow toxins into milk, have led to the recommendation of a 4-day withdrawal period (UK) before milk can be consumed directly from bracken-grazed dairy cows.

Oak (acorn)

Yew

Definition

yew (e.g., Taxus baccata—English yew, T. cuspidata—Japanese yew) contains a cardiotoxic alkaloid, taxine, as well as cyanide.

Clinical features

signs usually follow acute exposure and include nervousness, ataxia, dyspnea, and collapse. The opened rumen in 13.8 shows normal ingesta mixed with needle-like yew leaves. Cattle usually die minutes after ingesting a few mouthfuls of yew twigs or berries, typically encountered as fresh or dried clippings thrown over a graveyard hedge into a bare winter pasture. The lethal dose in adult cattle may be as little as 1 kg of leaves. Some cattle may survive up to 3 days before they die.

13.8 Yew poisoning: opened rumen with yew leaves

Management

oral B_₁₂, sucrose and also atropine have been suggested for treatment. Emergency rumenotomy may be considered for valuable animals.

Ragwort (seneciosis)

Definition

Senecio jacobea is one of many species of ragwort worldwide which contain the pyrrolizidine alkaloid jacobine, that causes acute and more often chronic liver disease. Several other plants e.g. Crotalaria, contain similar pyrrolizidine alkaloids which also can result in chronic hepatotoxicity.

Clinical features

early signs include dark-colored diarrhea, photosensitization, jaundice, abdominal pain, and central nervous system abnormalities. Prolonged ingestion (chronic exposure) results in progressive weakness, weight loss, and liver failure due to cirrhosis, and severe lung disease. In the mature Hereford cow in 13.9, the resulting right heart failure led to the edema affecting the ventral body wall, brisket, and head. Clinical signs may not be seen until several months after digestion, by which time the animal is no longer consuming the toxin, and diagnosis can be difficult. Liver biopsy may be useful for diagnosis. The fresh plant is bitter and usually avoided. Intoxication frequently occurs following its incorporation into conserved forage as this renders the plant more palatable. See also photosensitization (p. 30).

13.9 Ragwort poisoning (seneciosis): ventral edema of abdomen, brisket, and head

Differential diagnosis

mycotoxicosis (p. 253), lead poisoning (13.29), and other causes of hepatic disease and encephalopathy.

Management

no useful treatment for pyrrolizidine alkaloid toxicity. Remove clinically normal cattle to uncontaminated food supply. Avoid making hay or silage from ragwort-infested pastures, especially in late summer and autumn.

Rape and kale

Definition

some forms of forage of the Brassica family, such as kale and rape, contain glucosinolates which with plant myrosinase can be hydrolyzed to S-methylcysteine sulfoxide (SMCO) which can cause a hemolytic (Heinz-Ehrlich body) anemia following production of dimethyl disulfide by ruminal bacteria. The flowers and seeds of mature plants are particularly poisonous, whether ingested by grazing cattle or in cake or meal. Glucosinolates cause goiter, encephalomalacia (“rape blindness”), pulmonary edema, and interstitial pneumonia.

Clinical features

cattle develop hemoglobinuria, voiding dark-red urine (13.10), and are anemic and weak. Autopsy of fatal cases reveals pallor and jaundice of the liver (13.11) and heart (13.12).