Vet on Call: Bracken fern, the danger lurking in grazing fields

Most farmers believe that when a cow is served and two days later spots blood from the vulva, it broke its egg and, therefore, cannot conceive until it comes on heat again.

Yet, discharging blood from the vulva in a cow, after being served, has no relationship with conception.

The cow is simply bleeding from small blood vessels that had supplied the birth canal tissues with a lot of blood during heat. The vessels then break down after heat and bleed into the birth canal.

That is one of myths often repeated on farms to the point that it seems the truth.

It was, therefore, not surprising when Mwangi called me the other day from Ndakaini in Murang’a and asked, “Tell me doctor, can my cow survive after being pierced in the kidneys by bracken fern?”

I have heard this bracken fern kidney piercing story before, but I always like understanding how a farmer gets erroneous information and concretised it into fact. “So Mr Mwangi, what makes you believe bracken fern has pierced your cow’s kidneys?” I enquired.

He told me one of his Friesian cows started voiding brownish urine six months ago and this had progressed to bloody urine.

The problem had escalated despite countless treatments and now the cow was producing blood clots in addition to the bloody urine.

Mwangi further said an experienced dairy farmer in his village had informed him cows behave like that after eating the bracken fern plant.

COMMON IN WET HIGHLANDS OF KENYA

That the plant stem perforates the cow’s rumen and pierces the kidneys. It is the bleeding from the kidneys that causes the browning of the urine.

The “knowledgeable” farmer had also said bracken fern could sometimes pierce the heart, just like he had seen it happen with nails.

Now, it was clear that the “knowledgeable” farmer may actually have seen a cow with what is called hardware disease when a wire or nail is swallowed and then it pierces through the cow’s rumen straight to the heart. The animal dies of infection and damage to the heart and lungs.

Hardware disease is common in cattle fed on hay tied with wires or zero-grazed animals where nails fall from the wooden construction into the feeding trough.

I confirmed with Mwangi that his farm had a lot of bracken fern in the grazing fields. He told me the cow was feeding well and everything looked normal until she started urinating and one would see the blood-stained urine.

However in the last one week, the cow had started losing weight.

From Mwangi’s description, it was clear that his cow had bracken fern poisoning. The plant is ubiquitous in most wet highlands of Kenya.

I saw the poisoning for the first time when I was about 12. It affected my favourite cow in our herd. It was a big relief when our pathology lecturer, at the university, took us through the mode of action of bracken fern poisoning in cattle.

Mwangi was surprised when I explained to him the process of bracken fern poisoning in cattle. I could feel the elation in his voice as he now knew the solution lay with him.

TISSUE DAMAGE

He had to work very hard to clear the fern from his grazing area to protect the other cows.

As for the sick one, the best option was to destroy it and burry because bracken fern poisoning has no cure. Further, scientific research shows that humans could be exposed to bracken fern poisoning through milk from affected animal.

Bracken fern is present in high rainfall cool areas in many parts of the world. Except for young inexperienced animals, older animals only eat the fern accidentally when grazing, when it is inadvertently baled together with hay or during drought.

All parts of the fern are poisonous but young shoots and the thick invasive roots called rhizomes have higher toxin concentration than the leaves.

Cattle can accidentally eat the shoots when they are emerging from the ground among the grass. Sheep are more resistant to bracken fern poisoning than cattle.

The fern has a variety of poisonous compounds. Signs of poisoning seen in cattle depend on the type of toxin in the fern consumed, the quantity of toxin, the amount of fern eaten and how frequently the cow eats bracken fern.

One small accidental intake of fern may not cause any problem but repeated ingestion will result in tissue damage and signs of poisoning as seen in Mwangi’s cow.

Bracken fern poisoning occurs in two forms, sudden or acute and chronic. Mwangi’s was a chronic form of poisoning.

The animal initially shows brown urine due to destruction of red blood cells and slight bleeding in the kidneys and bladder.

AVOID EXPOSURE

The animal may also have fever and loss of blood demonstrated by pale mucous membranes, seen in the eye and the vulva.

As the poisoning progresses, the internal bleeding in the bladder and kidneys increases and the animal sheds blood in urine as Mwangi was seeing in his cow.

Bracken fern poisoning also causes cancer of the bladder and blood vessels and this increases the amount of blood that comes out in urine.

The animal loses weight and eventually dies. The chronic form is more commonly seen.

Cattle with acute poisoning die suddenly after consuming large amounts of bracken fern. Such animals show bleeding in the gums and eyes and through external openings.

Bracken fern poisoning may be confused with diseases such as anthrax, which cause bleeding from external body orifices and babesiosis and leptospirosis which cause bloody urine.

The only sure way of dealing with blacken fern poisoning is to ensure animals do not get exposed to it.

The plant should be eradicated in all grazing areas through manual removal or use of weed killing chemicals. Hay should be sorted carefully to ensure it does not contain bracken fern.

Fortunately for Mwangi, no any other of his cows has shown signs of bracken fern poisoning to date.