THE PREVALENCE OF ANTHELMINTIC RESISTANCE IN NEMATODE PARASITES OF SHEEP IN SOUTHERN LATIN-AMERICA - ARGENTINA

Sixty-five sheep farms in the northern provinces of Buenos Aires, Entr e Rios, Corrientes, Cordoba and Sante Fe were used in this survey on a nthelmintic resistance, Anthelmintic groups tested were the benzimidaz oles, levamisole, the combination levamisole + benzimidazole product a nd the avermectins. The overall level of resistance was 46% of propert ies, with resistance to the individual drug groups being 40%, 22%, 11% and 6%, respectively. On a large proportion of farms the resistance r ecorded was to two, or more, anthelmintic groups, Haemonchus contortus , Ostertagia spp. and Trichostrongylus spp, were the most abundant par asite species recorded. Resistance was greatest in the province of Cor rientes where the frequency of treatment is generally high due to the endemic nature of H. contortus. Management practices were also importa nt with resistance greatest on farms where frequent drenching is carri ed out and on farms carrying only sheep.