Poverty is higher in most African countries than elsewhere in the developing world, and highest in the rural areas. Accelerating growth in agriculture will therefore be critical to sustain growth and reduce poverty, but policy makers are unsure which sub-sector will yield the highest return for a given budget. This paper uses an applied general equilibrium model to simulate productivity gains in sub-Saharan agriculture subject to trade-offs between gains in crops and gains in livestock. The simulated results suggest three conclusions. First, most sub-Saharan economies gain more from research and development (R&D) investment in crops than in livestock, though the SACU (South African Customs Union) economies and Madagascar benefit from sharing it between crops and livestock. Second, when R&D is focused on food crops, sharing investment between crops and livestock also benefits other economies. Third, in economies where sharing R&D investment between crops and livestock is beneficial (e.g. Botswana), general economic growth boosts the benefits from R&D investment in livestock.