Population dynamics of gastrointestinal nematodes in a sheep flock in the province of San Luis

Abstract

The aim of this work was to describe the population dynamics of gastrointestinal nematodes (GIN) in a sheep flock in the central semi-arid region during the different seasons of the year. Fecal samples were taken monthly from sheep and lambs to determine the faecal egg counts (FEC) of GIN and coproculture for the differentiation of parasitic genera at larval stage 3 (L3). The L3/kg of dry matter (DM) present in the pastures was also counted and monthly rainfall was recorded. In both sheep and lambs, the tendency for egg shedding was similar, being higher around the periods of parturition and lactation (between 1.000 and 2.000 FEC). However, in lambs, the highest egg shedding was observed during primary infection with GIN (2.857 FEC). Haemonchus sp predominated in the coprocultures of both categories during most of the year, followed by Trichostrongylus spp and Teladorsagia sp, which did so in winter. The highest amount of L3/kg of DM was observed in the warm temperate months (up to 480 L3/kg of DM), where rainfall was also concentrated. Based on these results and the management of the farm, it is concluded that the appropriate times to deworm the flock are during the prepartum period with broad-spectrum anthelmintics, and a specific deworming against Haemonchus sp in lambs when they are around 4 months. Likewise, it is very important to establish an integrated control to reduce the risk of developing anthelmintic resistance.