An agro-economic simulation model was developed to facilitate comparison of the impact of management, market and biological factors on the cost of providing ruminant livestock with feed grown on the farm (home produced feed). Unpredictable year-to-year variation in crop yields and input prices were identified as quantifiable measures of risk affecting feed cost. Stochastic analysis was used to study the impact of yield and input price risk on the variability of feed cost for eight feeds grown in Ireland over a 10-year period. Intensively grazed perennial ryegrass was found to be the lowest cost feed in the current analysis (mean cost €74/1000 Unité Fourragère Viande (UFV)). Yield risk was identified as the greatest single factor affecting feed cost variability. At mean prices and yields, purchased rolled barley was found to be 3% less costly than home-produced spring-sown barley. However, home-produced spring barley was marginally less risky than purchased barley (coefficient of variation (CV) 0·063 v. 0·064). Feed crops incurring the greatest proportion of fixed costs and area-dependent variable costs, including bunker grass silage, were the most sensitive to yield fluctuations. The most energy input-intensive feed crops, such as grass silage, both baled and bunker ensiled, were deemed most susceptible to input price fluctuations. Maize silage was the most risky feed crop (CV 0·195), with potential to be both the cheapest and the most expensive conserved feed.