Thiamine - Why are my cows going blind?

STOCK THIAMINE DEFICIENCY

Why are my cows going blind?

Dietary changes, weaning and other stressors on cattle can cause vitamin B1 deficiency, which in turn can cause blindness. Dr Rory Dean describes the signs to watch for and what to do when you see them.

In 1884, Polish scientist Casmir Funk discovered four chemical substances were required in humans’ diets for essential functions. He found these substances seemed to contain an amine chemical group and he termed them “vital amines”, which would eventually be shortened to “vitamins”. One of the original four vitamins he discovered was thiamine, or vitamin B1. All ruminants have an essential requirement for thiamine, which helps support, among other things, a healthy neurological system.

In healthy ruminants fed sufficient roughage, plentiful thiamine is normally produced by thiamine-producing bacteria in the rumen.

Thiamine deficiency in cattle occurs under several circumstances that are not production of thiaminase, an enzyme that fully understood. breaks down thiamine.

Certainly, when cattle are fed diets Vitamin B1 is essential for energy supply containing insufficient roughage, to the brain in ruminants. Deficiency thiamine deficiency causes a type of degeneration is common, and this Conditions your vet may in the brain called is often a problem in consider for similar cases: polioencephalomalacia, feedlots around the • Lead poisoning which causes a variety of world. Changes in diet, • Salt poisoning symptoms. Affected animals weaning, physiological • Thiamine deficiency may appear restless, blind, stress, and sulphur show seizure activity, or toxicity following fertiliser application wander aimlessly. Often death ensues are commonly associated with thiamine within 24 hours. deficiency. The current and most likely theory for the progression of vitamin B1/ CASE EXAMPLE: thiamine deficiency in these cases is that During an August weekend, a contract the stressor causes a shift in the population milker sought veterinary advice for a cow of bacteria in the ruminal “soup”. This that had appeared to be aggressive and had change in rumen bacteria leads to shown seizure activity the night before.

Left: Lab tests allowed us to rule out lead toxicity in this case, and showed the animal had sustained muscle damage from bumping into things. Centre: Lab testing showed Blood Lead levels <0.02 mg/L 0 - 0. Right: Kiwi ingenuity! A veterinary colleague examines the heifer’s response to light using a small torch and a pair of overalls!

She was promptly treated by the farmer with calcium/magnesium and pain relief, but seemed to not respond to therapy. Owing to damage the animal sustained during seizures and being cast overnight, the decision was made to euthanise her on welfare grounds.

The following week, a first lactation heifer was presented to me as suddenly blind. She gave around 20 litres of milk the night before, and seemed normal. The staff reported her able to keep up with the herd in the morning, but when on her own she would walk into objects. She had reduced milk yield and had poor ruminal fill as if she hadn’t eaten overnight. On examination, I found her to be completely blind and showing evidence of not having eaten overnight. Other than some evidence of head pain, her neurological examination was normal. She was blood sampled and treated with Vitamin B1 (thiamine) and dexamethasone, a potent steroid anti-inflammatory medication. The following day the heifer appeared to be eating well, but was still blind. Subsequently, another first lactation heifer was found to be blind, with her head raised and showing a “high stepping” gait. She had clearly been having seizures, was covered in mud and was easily tackled to the ground in the paddock. She was given the same therapy comprising the vitamin

population, leading to thiamine deficiency. Most cases of thiamine deficiency are seen in young cattle under one year of age, so this was a challenging, unusual case. It was decided to orally drench all 200 heifers in the mob with thiamine powder made into a solution, and reduce the amount of starch in the diet. The two heifers that were treated by me were diligently treated with thiamine Vitamin B1 (thiamine) and dexamethasone. injections twice to thrice daily by staff, and continued to improve before regaining B1 injection and dexamethasone, and the their sight a week later. After the farm team first heifer was re-treated. Blood samples drenched the heifers and changed the diet, showed changes suggestive of muscle no further cases were seen. damage, which is caused when blind In summary, it is important to involve animals walk into objects, and the absence your veterinarian for advice and diagnosis of lead in the blood helped in managing unusual me rule out lead toxicity as the cause of the blindness. Some concern was raised over an old shed in the cases onfarm. Early action, diagnosis and treatment

The heifers were in paddock, as cattle can of the mob prevented great condition, and were get lead toxicity from old considerable losses in milking well. They had paint – thankfully, this was this case. Treating the recently been moved down not the case. individual cows without from the runoff, where consideration of the rest of kikuyu grass predominated, the heifer mob would have on to a diet comprising ryegrass, maize led to huge losses had this farmer not acted silage and distillers dried grains. While this early and aggressively. is a great diet for early lactation animals, Moreover, the diligent treatment and in this case the dietary change and the nursing care is the primary reason behind physiological stress heifers were under in the positive outcomes in the two heifers their first lactation may have contributed that were treated for thiamine deficiency to a change in their rumen bacteria in this case.