Helmintoses de ruminantes: i. viabilidade econômica do tratamento anti-helmíntico; ii. perfil da resistência anti-helmíntica de nematódeos gastrointestinais de ruminantes

Abstract

Resistance of gastrointestinal nematodes is an emerging problem in ruminant production in Brazil and other regions of the world, and is largely related to deficits in productive indexes due to its effects on the welfare and health of these animals. However, some aspects such as the economic impact resulting from this problem, for example, still need further investigation. Thus, the aims of this study were: (1) to verify the cost / benefit of the treatment with different anthelmintic compounds in the productivity of naturally infected animals in extensive system farms of beef cattle with different nutritional strategies after weaning; (2) to evaluate nematode populations in cattle and sheep that share grazing areas before and after treatment with different anthelmintics, and to evaluate the efficacy of these treatments on naturally infected ruminants from seven different farms. Additionally, for groups of cattle and sheep treated with a benzimidazole, we investigated the presence of co-infections by Haemonchus through polymerase chain reaction (PCR) evaluations. In Chapter 1, we evaluated the efficacy of five different anthelmintics and their relationship to the weight gain of calves under different diets after weaning by performing an economic analysis with the data obtained from 150 days of evaluation at four farms from Rio Grande do Sul state. In two of these properties, farms1 and 3, the most effective anthelmintic resulted in the highest financial return and in the others (farms 2 and 4) the ivermectin group 3.15% and control group, respectively, obtained the best results. In Chapter 2, we first evaluated six different anthelmintic compounds in the treatment of cattle and sheep and the nematode population present in these ruminants in shared grazing areas. The results obtained revealed a certain similarity both in the efficacy status of the products and in the helminths presents in these animals. In a second moment, we observed the presence of co-infection in cattle and sheep by Haemonchus species, especially in pre-treatment feces cultures, as well as the possibility of infection caused by hybrids of this parasite in one of the evaluated properties