Late last Spring, I got a call from one of my clients: one of their calves had become blind, staggery and had gone down. All the other calves seemed fine. This mob of calves had been weaned for some time, and there was nothing else exceptional from the history. Apparently, they had seen similar issues in calves the year before. 
 
There are several conditions that cause calves to be staggery, but very few cause blindness. The most likely causes are PEM, lead toxicity, or salt toxicity. And there was plenty of water (making salt toxicity less likely), and no lead batteries in sight! 
 
PEM, or polioencephalomalacia, literally means ‘grey brain melting’ – damage to the grey matter of the brain and spinal cord. In cattle, it is seen more often in well-fed, thrifty young animals – the ones you really don’t want to lose! It is caused by thiamine (vitamin B1) deficiency, which leads to brain swelling, blindness and nervous system issues. A certain type of damaging bacteria in the rumen overgrows and actively breaks down this valuable vitamin. A sudden change of diet to lush pasture, high levels of sulphur intake, and overdosing with levamisole drench have been linked to this condition. On physical examination, the sick calf was indeed, blind. It also had reduced mental awareness and had lost control of its legs. She hadn’t eaten for a few days either. It wasn’t looking good. 
 
The quickest way to diagnose PEM (and save the calf’s life) was to treat with thiamine (vitamin B1). I took some bloods to rule out other causes and left my farmer with enough vitamin B1 to dose the calf for the next few days. We moved her into a calf pen to keep her on meal, and out of harm’s way. 
 
The high dose of thiamine we give in these cases is designed to flood the body; so much so that the bacteria can’t break it all down. Even with prompt treatment, over 25% of affected animals will die, and if they are down before treatment, nearly all of them don’t make it. 
 
Luckily for this calf, we got the treatment in early enough. She made a full recovery. The brain has amazing regenerative powers, and if the swelling is reduced quickly enough, these animals can regain full use of their bodies, including vision. 
 
However, we then started seeing clinical signs in four other calves from the same mob. While possible, individually injecting calves with vitamin B1 at least once a day becomes costly – in terms of the drug itself and the labour time. Thiamine can also be given as an oral drench to the whole mob during the risk period. This needs to be given to each calf for 3 days in a row, and then ‘boosted’ every few weeks. It’s a much cheaper option and ensures no calf gets missed. 
 
If you have seen blind or staggery calves during the late Spring/Summer period on your farm, ask your vet about PEM. With quick and appropriate treatment, lives can be saved, and unnecessary losses prevented.