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Title: EFFECT OF PREVIOUS EXPOSURE ON ESTABLISHMENT OF CATLE NEMATODES AFTER NATURAL CHALLENGE EXPOSURE ON CONTAMINATED PASTURE

Author
item WILLIAMS, J - LSU BATON ROUGE LA
item Gasbarre, Louis
item KLEI, T - LSU BATON ROUTE LA
item DEROSA, A - LSU BATON ROUGE LA
item CHAPMAN, M - LSU BATON ROUGE LA

Submitted to: American Association of Veterinary Parasitologists Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/24/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: While it is generally accepted that exposure of cattle to gastrointestinal nematode infections induces some level of protective immunity upon rechallenge, little is known about magnitude or duration of exposure for such responses. It is commonly held that resistance develops faster and is stronger in intestional infections when compared to those of the abomasum. The purpose of this study was to assess the effect of a 3-6 month pasture exposure on parasite establishment after a second pasture exposure. Calves grazed on naturally infected pastures in Louisiana at times when: 1) the Ostertagia population would be largely inhibited larvae; 2) most Ostertagia would develop normally, or 3) over both time periods. All cattle were then housed to preclude further parasite exposure for an additional 6-9 months. At the end of this period all cattle were treated to remove residual worm populations and were placed back on pasture along with age-matched cattle that had been housed for the entire experiment, an with young cattle. Previous exposure resulted in reduced numbers of adult Ostertagia and a corresponding increase in the percentage of inhibited larvae, although the total number of worms was not reduced. In addition, worms were significantly smaller and less fecund. In comparison, previous exposure resulted in marked reduction in numbers of Haemonchus, Cooperia, Trichostrongylus, Oesophagostomum, and Trichuris, although a small percentage of cattle remained susceptible upon challenge. These results indicated that most cattle develop immunity to reinfection with most species after a relatively brief primary exposure. The exception is Ostertagia, but it is not the result of the site of infection as cattle were able to substantially reduce the numbers of other abomasal nematodes.