PHOTOSETNSITIZATION IN CATTLE GRAZING ON BERMUDA GRASS


 R. We. Kidder, D. V. Beardsley, T. C. Erwin

 For several years a skin disease of cattle has been observed on some
of the pastures in the Florida Everglades. The first cases were reported about
the time that "Aftosa" broke out in Mexico. These cases were examined thoroughly
in order that Aftosa be ruled out of the picture. Some veterinarians who saw
these animals thought that the burning came from copper sulfate which had been
dusted on the pastures and on them by airplane.

 As more cases developed the similarity of symptoms of this disease
with Lantana poisoning led to the study of weeds or other toxic plants. Several
of these suspected weeds were fed to cattle to check them for toxic symptoms with
negative results.

 Following the flood of 19h7 many of the St. Augustine pastures and other
better grasses were killed and replaced with Bermuda grass, the seed of which was
scattered by the flood waters. Closer observation showed that occurrence of this
disease was mostly on these and other Bermuda pastures. Some cases appeared in
1948 in the summer months of July and August. Other cases showed up in October,
but the severe outbreaks came during the winter or early spring.

 By the time these observations had been made, the disease had been quite
 thoroughly identified as a type of Photosensitization. This means that the af-
 fected animal had become unusually sensitive to sunlight and to consequent sunburn.

 A study of causes of Photosensitization revealed that some animals in-
 herit this tendency. However, it seems that this type of Photosensitization is
 rare. Some plants, such as St. Johnswort and Buckwheat, contain substances
 which show an intense red fluorescence. When these substances are absorbed by
 the blood they cause the animal to become sensitive to sunlight. This is called
 hypericismm" because the botanical name for the St. Johnswort family is Hypericum.

 The third type of Photosensitization is associated with a type of
 jaundice or icterus and is produced by the accumulation in the liver and the
 blood stream of excessive amounts of porphyrin called "phylloerythrin".
 Porphyrins are closely related to hemoglobin and chlorophyll and are part of the
 coloring matter in the bile; however, they differ chemically from bile pigments.

 The Photosensitization disease under consideration in this paper
 is the third type and is brought about by the inability of the animal, to
 excrete normally the phylloerythrin which is a digestive product from chlorophyll,
 the green coloring matter of grass. Normally phylloerythrin is excreted through
 the gall bladder, bile duct and intestinal tract. It is normally present in
 the contents of these organs of ruminants when they are on.pasture. Then this
 normal excretion is inhibited, the phylloerythrin is taken up in the blood and
 other body fluids, causing the animal to become sensitive to sunlight. When
 the phylloerythrin is excreted by the kidneys the urine becomes dark brown.


42 3.74