The suitability of a single mid-season targeted selective treatment (TST) for gastrointestinal nematode control, based on flexible average daily weight gain (ADWG) thresholds, was investigated in 23 groups of first grazing season calves 3-4 months after turnout (levamisole 7.5 mg/kg). In each group, animals were randomly allocated into 2 sub-groups: one sub-group where all calves were treated (whole treatment, WT) and the other sub-group where a TST was applied on the animals showing an individual pre-treatment ADWG inferior to the corresponding mean pre-treatment ADWG in the WT sub-group. At housing, blood anti-Ostertagia antibody and pepsinogen levels and breech soiling score were assessed at individual level. In TST sub-groups, the ADWG thresholds for treatment ranged from 338 to 941 g/day and the percentage of treated animals from 28 to 75 %. Pre and post-treatment ADWG as well as parasitological and clinical parameters measured at housing were similar between WT and TST sub-groups. In the 6 highest exposed groups (pepsinogen level ≥2.5 U TYR), the average effect of treatment on post-treatment ADWG was the highest and estimated up to 14 kg for 4 months of grazing. In contrast, in 6 other groups showing the lowest exposure, no effect of treatment was seen suggesting an absence of production losses when the level of infection is low. This study demonstrated that a mid-season TST strategy for first grazing season calves based on the use of flexible thresholds of AWG allowed similar growth compared to WT strategy while keeping a nematode population in refugia.