COW (case of the week): Alsike Clover

This week's COW is another feed related toxicity. It seems I have had a run of these lately. This time the offending agent was Alsike Clover. Here is a good picture of what this plant looks like. It can cause the skin to be hyper-sensitive to sunlight. We refer to that as photosensitivity. Photosensitivity causes the skin (almost always only the white skin) to sunburn extremely easily. For this reason we do not usually see these cases in the winter. However, when a horse gets exposed to a significant amount (usually more than 20%) of this in their hay and you get a good run of sunny weather like we’ve had for the past couple of weeks, then you can see these skin conditions. No one knows exactly what it is in Alsike clover that causes this syndrome, but we do know that it affects the liver, primarily the bile ducts, and the photosensitivity is the result of the effects on the liver.

The skin irritation with these cases can become quite extensive. As I mentioned earlier, it almost always just affects the white skin. Sunburn classically affects the muzzle- as it did in the case I saw this week. It also almost always affects the lower legs and at first glance looks a lot like ‘scratches’ of the lower limbs. Again, this usually only affects the white skinned areas. This presentation of lower leg dermatitis can make it a little difficult to sort out from regular ‘scratches.’ If there is any doubt, we can take some samples from the affected areas and look at it under a microscope. The other hint is that when you clip the skin, you will see evidence of diffuse skin irritation that goes beyond just the crusty areas you first noticed before clipping.

There is no specific blood test for Alsike clover toxicity, but we will often see elevations in liver enzymes. Treatment is fairly straight forward: remove the offending agent from the diet and treat the skin. So get a good look at this picture and check your hay or your pastures (once things start to grow again in the spring). If this stuff makes up more than 20% of the hay, find an alternate hay source.