Bovine blindness: Causes and prevention
Blindness is fairly uncommon in cattle, but it can occur for several reasons. Blind cattle may be seen circling, knocking into objects and have no menace response (i.e. they won’t blink when a hand is waved in front of their eye).
What Causes Blindness in Cattle?
Some of the most common causes are described below:
Normally seen in young beef cattle who are not being fed grass or other green foods, or who are born to cows on a poor, dry pasture. This leads to a dietary deficiency of the vitamin A precursor, carotene. Vitamin A is needed to regenerate retinal tissue and for normal growth of the cranial bones in the head. Deficiency in older animals can cause retinal dysfunction, and in younger animals the bone around the optic nerve fails to develop properly, leading to physical constriction of the optic nerve and subsequent blindness.
The first signs of vitamin A deficiency before complete blindness develops can include poor ability to adapt to bright light and night blindness.
The typical one-sided facial paralysis and circling caused by listerial encephalitis can also be accompanied by blindness in one (or occasionally both) eyes. Listerial infection of just the eye itself causes silage eye, and animals are often blind on the affected side.
Lead paint, batteries and pipes are all possible sources of lead on the farm and can be ingested by curious animals. Affected animals will initially salivate and then become ataxic and blind. Convulsions, coma and death may follow.
Some animals will show colic signs due to the lead irritating the alimentary mucosa. Lead poisoning can be diagnosed by measuring lead concentrations in blood samples.
Vitamin B1 is destroyed in the rumen by the microbial enzyme thiaminase, produced by Bacillus spp. and Clostridium sporogenes, leading to a deficiency. These bacteria grow quickly when animals are fed a high concentrate diet or one containing high ammonium sulphate levels, commonly used to prevent bladder stones.
CCN is most frequently seen in 3-6-month-old calves and can be seen in individuals or groups.
Calves will appear to be blind. Inco-ordination, head pressing and frothy salivation is followed by recumbency and then death. These cases must be treated as soon as possible – full recovery is possible if treatment is begun quickly enough.
Closantel has a narrow safety margin compared to other drugs, therefore toxicity is more likely to occur. Blindness is a consistent clinical symptom.
To diagnose toxicity, brain histopathology is needed to check for concentration levels. It is important to accurately weigh animals before treating them with closantel to dose as accurately as possible, and any combination products should be thoroughly mixed.
If you have any concerns about eye conditions or blindness in your cattle.