PARASITES AXD PARASITIC DISEASES OF HORSES 25 



as strongylidosis, results when blood strongyles occur in large numbers 

 and in association with other species of roundworms in the large gut, 

 particularly when horses are kept on permanent pastures. 



This condition is widespread in horses and is usually more injurious 

 to foals and young horses than to older horses. Strongylidosis is 

 frequently mistaken for infectious anemia or swamp fever and cases 

 diagnosed as swamp fever, in many instances, have cleared up follow- 

 ing the removal of worms by medicinal treatment. The common 

 symptoms of strongylidosis are diarrhea, weakness, and emaciation. 

 The digestive disturbances result from the irritation to the lining of the 

 gut produced by the parasites. At first the diarrhea is slight and the 

 soft manure has a bad odor and contains poorly digested food material; 

 later the diarrhea becomes more pronounced, with softer feces. The 

 appetite, which is irregular at first, becomes poorer and finally the 

 horses are off feed. As a result of their weakened condition, affected 

 horses find difficulty in chewing, may throw out mouthfuls of feed, 

 and then reject feed altogether. This leads to further emaciation 

 which becomes very marked. As the disease progresses the bones 

 become prominent, the coat becomes rough, the eyes are sunken, 

 and the animal becomes greatly weakened (fig. 17). With these 

 symptoms there are marked changes in various tissues and organs of 

 the body. 



The working capacity of horses which are suffering from strongy- 

 lidosis is decreased considerably even before the symptoms become 

 very pronounced, and in the absence of treatment such horses are 

 able to do less and less work as the disease progresses. It has been 

 found that when horses are treated for the removal of parasites 

 many of the symptoms described above disappear, the animals take 

 on weight, regain their working capacity, and make general improve- 

 ment. 



Treatment. — Phenothiazine is very effective for the removal of large 

 strongyles and is a drug which has come into wide use as an equine 

 anthelmintic. The fact that horses occasionally react unfavorably to 

 this drug has not been fully explained, although there is evidence that 

 animals on a low protein diet may be more susceptible to the develop- 

 ment of anemia, jaundice, and other symptoms of intoxication than 

 animals maintained on rations of adequate protein content. During 

 recent years, moreover, most of the risk of employing phenothiazine 

 as an anthelmintic for horses has been overcome by administering 

 smaller doses than had been used formerly and by giving the drug in 

 divided doses. The optimum dose for a mature horse of average size 

 is about 30 grams of the chemical, and it may be administered in gelatin 

 capsules, as a drench in suitable suspension, or admixed with grain 

 feed. Moreover, if the last method is followed, effective medication 

 may be achieved by the administration in feed of 5 grams of pheno- 

 thiazine daily for from 5 to 7 days in succession as an alternative to 

 giving the full dose at one time, the period depending somewhat upon 

 the size of the animal. Preparatory fasting and purgation are not 

 necessary when phenothiazine is used, but it is desirable in the interests 

 of safety to guard against constipation when the treatment is given. 

 The addition of bran to the feed mixture is helpful in this respect. 



Although heavily parasitized equines should be given therapeutic 



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