Sustainable intensification is a strategy contributing to global food security. The scope for sustainable intensification in crop sciences can be assessed through yield gap analysis, using crop growth models based on concepts of production ecology. Recently, an analogous cattle production model named LiGAPS-Beef (Livestock simulator for Generic analysis of Animal Production Systems – Beef cattle) was developed, which allows yield gap analysis in beef production systems. This paper is the first to assess yield gaps of integrated feed-crop livestock systems, to analyse underlying causes of yield gaps, and to identify feasible improvement options. We used grass-based beef production in the Charolais area of France as a case study. To this end, we combined LiGAPS-Beef with crop growth models that simulate grass production (fresh grass under grazing, grass silage, hay) and wheat production (concentrate). Feed crop and cattle production were integrated to simulate potential and resource-limited live weight (LW) production per hectare. Potential production is defined as the theoretical maximum LW production per ha, in the absence of resource or management limitations. Resource-limited production is determined by availability of one or several resources: water and nutrients for crops, and feed quality and quantity for animals. Potential production of a cattle herd with an ad libitum diet of grass silage was 2380 kg LW ha−1 year−1 and resource-limited production was 664 kg LW ha−1 year−1. Actual LW production (354 kg LW ha−1 year−1) was 15% of the potential production, implying a relative yield gap of 85%, and 53% of the resource-limited production, implying a relative yield gap of 47%. Applying yield gap analysis disentangled the major biophysical causes of these yield gaps: feeding diets other than the ad libitum grass silage diet, water-limitation in feed crops, and sub-optimal management. These yield gaps suggest scope to intensify beef production. We demonstrate, however, that yield gap mitigation decreased the operational profit per kg LW under the European regulations for bovine and grassland premiums operational in 2014. Hence, as expected, the premiums aiming to support farmers' income and to promote sustainable agriculture and rural development were not conducive to narrow yield gaps at the same time. The current common agricultural policy (CAP, 2015–2020) provides more scope for intensification, such as increasing stocking density via better grassland management.