References
Summer poisoning hazards
Abstract
There is a seasonal risk with some poisons and in the summer, when stinging insects and adders are more active, there is a risk of envenomation. Diagnosis of an adder bite may be missed in horses, as the biting event is rarely witnessed. Envenomation may result in local swelling and occasionally, systemic effects. Multiple bee stings are particularly hazardous as this can result in multi-organ involvement, which may be fatal. Grazing on some plants, such as ragwort or bracken, for a prolonged period can also result in poisoning as ragwort contains pyrrolizidine alkaloids which cause liver failure and bracken contains an enzyme that has an anti-thiamine effect, inducing thiamine deficiency. Photosensitisation following exposure to plants containing phototoxins and bright sunlight is also a risk in summer. Treatment of plant poisoning in horses is generally supportive and involves removing the plant, providing good quality food and supportive care. Thiamine supplementation may be required in severe cases of bracken poisoning. Animals should be protected from sunlight following exposure to a phototoxin, with supportive management of skin lesions. Management of adder bite is supportive with administration of adder antivenom. Multiple bee stings require aggressive supportive care.
Adders and stinging insects are more active in the warmer months, so the potential risk of horses being bitten or stung is increased. Bright sunlight increases the risk of photosensitisation following exposure to plants containing phototoxic chemicals, and grazing on plants that can be toxic with prolonged exposure may also occur over the summer months (and in the winter if the plants contaminate hay).
This article briefly discusses some of the seasonal summer poisoning hazards for horses. If more detailed information is required when managing a case, consult a veterinary poisons information service (Box 1).
Box 1.Veterinary poisons information services
European adders (Vipera berus berus, Figure 1) are most active in the summer. Although relatively common in dogs, envenomation from an adder bite can also occur in large animals including horses. Adders may not be seen to bite a horse, but envenomation should be part of the differential diagnosis in a horse with localised limb swelling that spreads up the leg. Close examination may reveal puncture wounds. Envenomation can cause significant morbidity but low mortality; and horses may be bitten on a limb or the face (Arbuckle and Theakston, 1992; Anlén, 2008).
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