The objective was to evaluate the effect of different cultivars of Brachiaria brizantha on the dynamics and concentration of the larval stages of gastrointestinal nematodes in the soil and forage strata, as well as their effects on the performance of naturally infected lambs. Overall, 48 90-day-old lambs with an initial weight of 19.04 ± 0.96 kg were observed. Moreover, a randomised block factorial design with four cultivars of Brachiaria brizantha (Marandu, Xaraés, Piatã and Paiaguás grasses) under intermittent stocking (with a pre-grazing canopy height of 40 cm and post-grazing canopy height of 20 cm) for two grazing cycles was used. The following variables were analysed: faecal egg counting, faecal culture, mean corpuscular volume, FAMACHA© score, weight and body condition score, the recovery of larvae from pasture and soil samples, nutritional value and the production and structural components of forage. Lambs grazing Marandu grass demonstrated the highest level of nematode infection (P < 0.05). However, the nutritional value did not differ between cultivars. Marandu grass had the highest pasture density (P < 0.05), while Paiaguás grass had the highest percentage of dead material (P < 0.05). The various genera of gastrointestinal nematodes found in the faecal cultures, regardless of the cultivars, include Haemonchus (92.01%), Trichostrongylus (4.55%), Strongyloides (3.06%) and Oesophagostomum (0.37%). Lambs grazing Xaraés grass had the lowest body weight (P < 0.05). Furthermore, larvae concentrations were highest in Marandu and Paiaguás pastures; infective Haemonchus and Trichostrongylus larvae were recovered from pasture and soil samples. The different cultivars of Brachiaria brizantha produce diverse and relevant microclimatic conditions to contaminate soil, pastures and animals. Animal performance was not compromised despite the Marandu and Paiaguás cultivars having the highest levels of contamination and infection. Based on parasitological aspects, the Brachiaria brizantha cultivars Xaraés and Piatã are recommended for grass-based sheep production systems over the other cultivars since they contribute to the reduction of larval contamination and infection.