Date of Award:

5-1-1969

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Zoology

Committee Chair(s)

Datus M. Hammond

Committee

Datus M. Hammond

Committee

Merthyr. L. Miner

Committee

Donald V. Sisson

Abstract

The effectiveness of amprolium administered in the grain in controlling Eimeria bovis in calves 2 to 4 months old, the stage or stages of the parasite affected by amprolium, and the nature of this effect were studied. Another drug, MK-183, administered orally in capsules, was also tested. Calves with fistulas were used to study the early stages in the life cycle of this coccidian. Six experiments with a total of 79 calves were conducted. Four experiments involved amprolium and two involved MK-183. All calves were Holstein-Friesian males, obtained when new-born. When the calves were 2 to 4 months old, each was given 50,000 E. bovis oocysts. In three of the amprolium experiments one or two calves from each group were killed 14 to 19 days post-inoculation to investigate the cytological effect of the drug on the parasite. Tissues were collected and prepared by routine histological methods. Excysted oocysts were introduced into an intestinal fistula in each of six calves to study the early stages of the parasite. Amprolium, administered in the grain at 25 or 5 mg/kg for 21 days beginning on the day before inoculation, effectively controlled coccidiosis. The results in the amprolium-treated calves differed significantly (at the .01 level) from those in the untreated calves. The peak in oocyst discharge occurred 4 to 7 days later in the calves treated with amprolium at 25 mg/kg than in the untreated calves, but a delay in oocyst discharge occurred in only two of the 10 calves treated with 5 mg/kg of amprolium. MK-183 at dosage levels of 100, 10, 5 and 1 mg/kg effectively controlled coccidiosis when administered for 5 days, beginning 12 days after inoculation. In two experiments no schizonts were found in treated or untreated calves killed 14 to 19 days after inoculation. In the third experiment with calves given 25 mg/kg of amprolium, and killed 14 to 19 days after inoculation, most of the schizonts observed were smaller in size and in an earlier stage of development than those in the corresponding untreated calf. Only one such retarded schizont was seen in the calf treated at 5 mg/kg and killed 14 days after inoculation. The host cells of the retarded schizonts were more hypertrophied than normal. The host cell cytoplasm had three distinct layers, whereas only two layers were present in the cytoplasm of schizonts of untreated calves. Numerous small, granulated vacuoles were observed within the cytoplasm of the host cell of the retarded schizonts. Some of the retarded schizonts appeared abnormal, and some, especially in the 19- day calf, were apparently degenerate. Many more schizonts were seen in the 25 mg/kg-treated calf killed 19 days after inoculation than in the untreated calf. The results indicated that the first-generation schizont stage was affected by the amprolium. Early stages of Eimeria bovis were observed in sections of a fistula in one calf killed 5 days after introduction of sporozoites. The stages included sporozoites, trophozoites, as well as 2-, 3-, 4-, and 5-nucleate schizonts. Measurements and detailed descriptions of these stages were presented.

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