Author
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Gasbarre, Louis |
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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: Effective and efficient control of GI nematodes in cattle requires administration of modern anthelmintics at strategic time points. The most important target species is Ostertagia ostertagi. The pre-eminence of Ostertagia is due to both a high pathogenicity, and to the fact that strong gprotective immunity is very slow to arise. Recent observations on the biology of Ostertagia should influence the development of control programs. First, Ostertagia is among the most environmentally tolerant parasite species and can be transmitted year-round in many areas of the US. Transmission is reduced by sub-freezing temperatures and extreme drying conditions but the rate of transmission quickly rebounds as conditions change. Environmental tolerance means that substantial overwintering of larvae on pastures occurs and may be more important than arrestment in maintenance and transmission of parasite populations in these areas. Second, fecal egg determinations (EPG) do not accurately assess the numbers of Ostertagia in an animal, but instead measure the presence of more fecund trichostrongyle species, and animals with the greatest parasite-induced morbidity may not have high EPG values. Therefore, EPG values are of little value when used on individuals, and should only be used as a herd measure. Related diagnostic procedures such as fecal culture and larval differential can give misleading information unless conditions are carefully defined. Finally, intensive rotational grazing programs can result in the emergence of parasite-induced productino losses. This can be corrected by greater attention to parasite ocntrol in the intial development of the rotational program. |
