A discussion support model for a regional dairy–pasture system with an example from Réunion island U.B.NIDUMOLU 1 *, M. LUBBERS 2 , V. ALARY 3 , P. LECOMTE 3 AND H.VAN KEULEN 2 1 Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), Département ES (Département Elevage et Médecine Vétérinaire), Pôle Elevage, Station de Ligne Paradis, 7 chemin de l’Irat, F 97410, St Pierre, île de la Réunion, France 2 Group Plant Production Systems/Plant Research International, Wageningen University and Research centre, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands 3 Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), Département ES, Campus International de Baillarguet – 34398 Montpellier, Cedex 5, France (Revised MS received 22 November 2010; Accepted 7 December 2010; First published online 18 February 2011) SUMMARY Réunion Island, situated in the Indian Ocean, presents a unique case study for modelling regional bio-economic parameters of the dairy industry. It is a good example of a closed system for several parameters of the model such as movement of animals, labour, consumption and available land. The existence of several agro-ecological zones from tropical to temperate, and various different types of terrain and vegetation presents another unique opportunity to study the impact of these features on the dairy industry. The present study models the dairy sector at a regional (island) level to study the impact of new or adapted agricultural policies in relation to changes in subsidy levels, price fluctuations and environmental policies (mainly nitrogen management). The model can be used to generate a number of scenarios to explore the effects of various policy measures, such as fixing the stocking rate according to EU norms, increasing or decreasing the milk subsidy, intensification (such as an increase in milk production to the allotted quota of 40 million litres/yr) and varying labour/price constraints (such as a reduction in labour hours or an increase or decrease in the milk price). The model is being utilized by the local dairy cooperative as a discussion support tool to study the implications at the regional scale of expanding the sector and assessing its economic, environmental and social impact. INTRODUCTION Dairy farming, along with other agricultural activi- ties, is facing important changes such as public policy change and/or climate change (Thornton et al. 2008). Anticipating these changes and evaluating them is critical for appropriate exploration of the future possibilities for dairy farming. In contrast to farming systems based only on annual crops or short cycle animal species, the functioning of dairy farming depends on complex interactions between past and present decisions, the consequences of which are extended into the future. For instance, changes re- sulting from decisions regarding fodder improvement or the replacement of breeding stock will be seen within a short time frame, while the impacts of changes in agricultural policy might only be seen in the long term. Therefore, a combination of top-down and bottom-up approaches is needed to improve the decision-making processes, both at the farm (bottom- up) and the sector (top-down) levels. It is also critical to consider the consequences of environmental and agricultural policy measures. The current paper focuses on the development of a regional dairy sector model for the island of La Réunion, France. The model ‘Ksheera’ was developed as a follow-up to earlier farm-scale modelling work (Alary 2004). The objective of the current study was to scale up analysis of the dairy sector to regional level by developing a discussion support tool for regional decision makers. The strength of the regional dairy model ‘Ksheera’ is that it integrates the complexities of dairy herd dynamics, animal nutrition, labour use, * To whom all correspondence should be addressed. Current affiliation: CSIRO Ecosystem Sciences, Adelaide, Australia. Email: uday.nidumolu@csiro.au Journal of Agricultural Science (2011), 149, 663–674. © Cambridge University Press 2011 doi:10.1017/S0021859611000165 663