Her head is red and swollen, her eyes are puffy, red and closed, her ears are droopy and she is itching her face excessively. What’s going on? What is this?
Diagnosis: Photosensitivity. You must act immediately
One afternoon we went out to check on our dairy sheep and discovered that one of them had a hugely swollen face. The following day some of the other sheep also had swollen faces. Turns out it was a photosensitivity reaction.
Photosensitization is something that we have never had to deal with prior to this. It went away as fast as it arrived, and to this day we have no idea what the cause was. Interestingly about the same time we had a photosensitivity problem with our sheep several other people in the area were asking on Facebook about the cause of similar symptoms in their sheep.
Photosensitivity is an allergic reaction to the sun. As you can imagine, being allergic to sunlight can spell big problems for livestock who spend their whole entire lives outdoors in the sun. Any animal, and even humans can have a photosensitivity reaction. It is not the same thing as a sunburn. The immune system is actively reacting to the sun and damaging the epidermis from within.
Photosensitization is a bit unique in that it does not affect animals of different colors equally. Typically photosensitization is limited to white animals or white portions of colored animals. Pigmented skin and areas covered with a thick layer of hair don’t typically suffer from photosensitivity. However they still can be affected if the reaction is severe enough.
Photosensitivity always has an underlying cause
With the exception of a congenital disease present in a few breeds, animals do not just spontaneously become allergic to the sun. There is an underlying cause that is making them hypersensitive. This underlying cause is typically liver damage due to a toxin of some sort. Livers are excellent at regenerating themselves, and sometimes this damage may be reversed. Sadly in many cases the damage is permanent. Sometimes it is severe enough that the whole flock needs to be culled because they will never be able to tolerate sun exposure again.
It is also possible for an animal to ingest a plant like buckwheat that directly causes photosensitization without liver damage. In some instances it may be caused by medications. However, these scenarios are much less common than liver damage.
There are a variety of plants that can cause photosensitization. Unfortunately it is tricky to study and discover what component is actually causing it. This is because these plants do not always cause photosensitivity when ingested. There are case studies where alfalfa and bermuda grass have caused photosensitivity. Both are considered excellent forages and typically do not cause any problems. What makes it even more complicated, is that it is possible that the ingestion of an insect or fungus growing on the plant caused the reaction not the plant itself.
This turned out to be the culprit in once case study. In this particular instance, the shepherd had mowed their pasture and allowed the grass clippings to lay there. This normally isn’t a problem. In that particular year the conditions were exactly right for a certain mold to grow on the grass clippings. The sheep ate enough of the mold when grazing near the grass clippings to cause liver damage and the resulting photosensitivity.
How does liver damage cause an allergic reaction to the sun?
This is an excellent question! There is a substance called phylloerythrin that is derived from the break down of chlorophyll (what makes plants green) in the digestive tract. Phylloerythrin is a photosensitizing agent which is typically efficiently excreted by the liver. If the liver is damaged by some sort of toxin, it cannot remove the phylloerythrin from the blood like it should. When this happens the phylloerytherin reaches the skin of the animal where it can react with the sun and cause damage.
Though this is a much less common scenario, it is also possible to temporarily cause too much phylloerythrin to be present in the blood without liver damage. This is possible to cause by suddenly moving animals from a dry desert pasture to a lush irrigated pasture.
Fortunately, the treatment for photosensitization is very straight forward
Affected animals need to be removed from access to the photosensitizing/liver damaging agent and immediately removed from sunlight. They should be kept in a dark barn until the symptoms have subsided. Moving the animals into the dark is essential to do quickly once you notice a problem. If the animal remains exposed to the sun the damage will continue to worsen. It will cause them a lot of pain and serious tissue necrosis will occur.
Sadly this damage is sometimes irreversible
Unfortunately, in most cases of photosensitivity we are dealing with a liver toxin and thus liver damage, and there are no guarantees. If the sheep’s liver can heal enough to resume removing phylloerythryn efficiently, they can return to grazing out in the sun. Sadly in some cases the liver damage is so severe that the reaction immediately returns upon sun exposure. These animals often must be culled for their own well being.
In the case of our sheep, we are not sure whether there was any liver damage involved. We hypothesized that it may have been the bermuda grass in their pasture. Or it could have been an over abundance chlorophyll exposure resulting from us allowing them access to a small patch of irrigated corn during a drought. Both seem unlikely, but we don’t know. What we do know is that there was a brief photosensitivity ‘outbreak’ on various farms in the area around that time. So perhaps due to the drought there was an unusual toxin affecting this area.
Regardless, we pulled the sheep from the pasture, put them inside eating hay and they all recovered within a couple days. In a couple weeks, they were able to return to the same pasture without issue. Thankfully none of them had any serious tissue damage to their skin, and they have been perfectly fine ever since.
How did we know our sheep had photosensitivity?
The first sign that something was wrong was seeing a sheep with a hugely swollen head. Her ears were flopped down, and she was clearly uncomfortable, agitated and repeatedly rubbing her swollen face. Upon closer inspection it was easy to see that her skin was red and angry looking. This was particularly obvious in the areas on her head and ears where the hair was thin. Her skin was also leaking yellowish sticky serum.
These are all textbook early symptoms.
If you see these symptoms in your flock get your sheep out of the sun IMMEDIATELY. Don’t wait to see if it goes away. Our sheep went from being fine at morning check to being so swollen they couldn’t see by mid afternoon. The reaction happens fast and the damage and discomfort continues to worsen until they are out of the sun.
If you do not help your animals quickly, they will have ever increasing damage to their skin which results scab formation and eventually necrosis. It can get bad enough for their skin to slough off and can result in them losing parts of their ears. At this stage they are in extreme pain, and highly prone to getting secondary infections. As you might imagine, at this point the prognosis is not good.
Thankfully, our sheep did not develop scabs or obvious lesions. The swelling went away within 48 hours of taking them off the pasture. We will note there was some tissue damage though. A couple weeks later our sheep lost all the hair on the backs of their ears and tops of their heads where they received the most sun exposure. This resulted in a new temporary problem—sunburn. We ended up putting sunscreen on their bald patches for a few days while we waited for the new hair to grow in.
Can you prevent having problems with photosensitivity?
Sort of. The obvious answer is to avoid allowing any weeds that are known photosensitizing agents to grow in your pastures. Also avoid feeding water damaged or moldy feed because they may contain fungi that cause liver damage.
Unfortunately there is no way to fully protect your animals. Sometimes we have no idea and are never able to figure out what the causative agent in photosensitivity is. That is why it is important to know the signs and symptoms of this less common ailment. That way you will be prepared to take action immediately to prevent more serious damage and suffering if this ever occurs in your flock.
We hope you never have to deal with this photosensitivity. However, if you ever see your sheep with a swollen face and floppy ears, you now know what to do to help them!
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