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Title: PARAMETERS EFFECTING FAECAL EGG COUNTS DURING EXPERIMENTAL INFECTIONS OF SHEEP WITH HAEMONCHUS CONTORTUS

Author
item FETTERER RAYMOND - 1265-20-00
item CORBIN C JEAN - 1265-20-00

Submitted to: Society of Washington Journal of Helminthological
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: The sheep stomach worm, Haemonchus contortus, is an economically important parasite of grazing sheep in many parts of the world. This parasite is also an important model for the study of intestinal parasites of cattle and other grazing animals. In order to determine the optimal time and concentration of egg production by female worms, variables such as age of lamb, sex, breed, dose of infective larvae and time of year were studied. The effects of these experimental variables on egg production were analyzed coincidental to experimental collection of parasite material. The results of the study reinforce the the finding that age of lambs and dose of inoculum, simultaneously, impact on egg production. These findings will also aid in reducing animal usage for experimental infections.

Technical Abstract: Egg output in eggs per gram of faeces (EPG), was analyzed to determine the effect of factors such as sex, breed, age, dose level of larval inoculum, and seasonal effect on Haemonchus contortus egg production. This study was coincidental to experimental collections of parasite material, spanning 7.5 years, and on a total of one-hundred- twenty-three lambs. Breed of lambs (Polled Dorset and Dorset/Suffolk mix) had no effect and sex had only marginal effects on parasite egg production. Lambs less than 90 days of age given 21,000-40,000 infective larvae and lambs 90-120 days given 11,000-20,000 infective larvae produced the highest egg concentrations. Seasonal effects on egg production were most noticeable in older lambs (121-210 days) with two peaks of egg production noted in May and September. These results support a conclusion that, simultaneously, age of lambs and dose of infective larvae impact on parasite egg output. Because of high mortality in the <90 day-old group, experimental infections can be most efficiently obtained by administering inoculations of 11,000-20,000 infective larvae in lambs of 90 to 120 days of age.