Signs of Snake Bite in Horses

Horses are highly susceptible to snake venom. As with cats and dogs, signs of envenomation are diverse and variable.

Such signs, which appear after a latent period (inversely proportional to the venom dose administered) include muscle tremor, respiratory distress with alae nasae and abdominal muscles working prominently, combined with little thoracic movement. Pupillary dilation, absent light reflexes (but may have positive eye preservation reflex), excessive sweating and salivation are also characteristic of this envenomation. The facial muscles may be unusually irritable. Paresis, preceded by muscular twitching, occur first in the hind limbs, and then successively in the fore limbs, thorax and neck. The abdominal muscles appeared to be affected only very late. The paralysis developed in 6-19 hours after experimental tiger snake envenomation, whilst death from respiratory failure occurred in 13-50 hours.

Similarly rapid effects were observed after experimental brown snake envenomation; within 3 hours the animal showed lassitude and was bleeding from the nostrils; the paralysis was well developed within 6 hours. There was dyspnoea and the breathing was diaphragmatic in type. At post mortem extensive haemorrhages were seen in the heart, lungs and kidneys. Numerous petechial haemorrhages were present in the bladder mucosa, though neither haematuria nor haemoglobinuria was observed.

Presentation may also vary between adults and foals. For example, brown snake bitten foals have been initially observed to be slow moving with a goose stepping type of leg action and to be taking frequent rests when suckling. After the tongue became paralysed, milk could not be swallowed and it ran back out of the foal's nose when the head was lowered. Death followed a period of lateral recumbency and laboured respiration. Adult horses by contrast, could not swallow, had uncoordinated gaits and showed muscle twitching and heavily laboured abdominal breathing.