In order to understand the farm-scale balance between the apparently conflicting objectives of system production and biodiversity conservation in grassland-based beef suckler systems, we constructed the whole-farm simulation model SEBIEN. SEBIEN uses a bio-technical approach focussed on grassland utilization by the herd to predict the daily functioning of suckler systems based on permanent pasture. The farming system is divided into three main components which interact at multiple time scales: (i) management, divided into a strategic component (management plan) and a tactical component (management rules), (ii) herd, divided into a group of cows with calf and a group of heifers, and (iii) feed, comprising grasslands paddocks, conserved forage and purchased feed (hay and concentrate). Each component is the subject of a sub-model. The dynamic models predicting animal intake and performance and permanent pasture growth, structure and digestibility have been published previously. The management sub-model is described. The inputs to SEBIEN include farm structure (= description of herd and grassland resources), management plan (= animal production objectives and grassland utilization), thresholds for management rules and weather data which introduces variability between seasons and years. The outputs of SEBIEN include the daily operation of the forage system, the dynamics of intake and performance for the average animals of the herd, and the dynamics of grassland production and utilization on each paddock. To characterize the production – biodiversity trade-offs at farm scale, we translated these outputs into an indicator of system production based on animal sales and forage self-sufficiency, and into an indicator of floristic diversity based on soil fertility and grassland utilization rates on each paddock. We simulated three case studies based on real farms with SEBIEN, compared their balance between production and floristic diversity and its response to biodiversity-friendly management rules such as late hay harvest and low grazing intensity. SEBIEN predicted that animal production was not systematically in conflict with floristic diversity at farm scale. The balance between grassland productivity and stocking rate was determinant for both floristic diversity and forage self-sufficiency. For all farms production remained unchanged when intermediate levels of biodiversity-friendly management rules were applied (40% of hay paddocks cut after flowering, or paddock change at grazing when sward height dropped under 8 cm). Though, the pattern and amplitude of the responses differed between farms. At farm scale, an increase in floristic diversity on a few paddocks sometimes led to a decrease on other paddocks, which confirms that farm-scale analysis are needed to evaluate the effects of field-scale environmental policies.