Managing livestock on lush feed

The sunny weather and lush green feed of spring are likely to bring increased incidence of photosensitisation in cattle and sheep during the coming weeks.

The term photosensitivity means an increased sensitivity to ultraviolet light and resembles a bad case of sunburn.

When grazing lush green feed, cattle and sheep take in large amounts of the plant pigment, chlorophyl.

After the pigment is absorbed from the digestive tract, it passes to the blood and is normally filtered by the liver, broken down and passed out of the body.

If an excessive amount of chlorophyl is ingested, its end products may not be fully removed and may build up to high levels in the blood.

This may also happen if the liver function is impaired in some way, for example, by damage from liver fluke or toxic plants such as Heliotrope and Paterson’s curse. St. John’s Wort has high levels of these pigments preformed in the plant.

The pigment then accumulates in the surface layers of the skin.

The interaction between the pigment in the skin and ultraviolet light results in a burn like effect in the skin.

The ultraviolet light must be able to penetrate the surface skin layers. This happens on uncoloured, less hairy areas of the skin such as the unpigmented skin and teats of cattle and the ears and nose of sheep.

In the early stages of photosensitivity an affected animal becomes agitated due to the burning sensation in their skin.

They shake their heads, rub against trees and kick at their bellies in an attempt to relieve the pain. Their ears may become swollen and droopy, and they seek shade during the day.

Photosensitivity can be severe enough to put an animal into shock which can be fatal.

Many times farmers only see the end results of photosensitivity where the affected skin begins to lift off as a result of the damage the burn has caused.

If detected in the early stages, antihistamines may help. There are ointments available for darkening teats which are particularly useful for dairy cattle.

Draw for 12th and 13th October 2016:

1. Landmark, 2. Scotts, 3, Elders, 4. SEJ, 5. Gibbon.