Greater farmer investment in well-formulated diets can increase liveweight gain and smallholder gross margins from cattle fattening

•To improve the productivity of smallholder cattle fattening, farmers will need to invest in higher quality concentrate-based diets which provide a return greater than the additional feed costs.•Even though concentrates are expensive, if they result in higher growth rates then they are far more profitable than zero-cash outlay feeding strategies.•Including opportunity cost of labour for forage harvest makes most forage feeding of cattle even more unprofitable. To improve the productivity of smallholder cattle fattening, farmers will need to invest in higher quality concentrate-based diets which provide a return greater than the additional feed costs. This research assessed two formulations of elephant grass, cassava bagasse, palm kernel cake and copra meal mixes for average daily liveweight gain (ADG) and income over feed cost (IOFC), compared to a forage diet in a pen experiment; and then evaluated the best performing diet as a supplement to existing smallholder bull fattening diets in villages in East Java, Indonesia. In the pen experiment, 24 Ongole bulls were allocated to three treatment diets fed at 25 g DM/kg liveweight.day in a 12-week randomised block experiment: 1) Elephant grass only; 2) a simplified feedlot diet (elephant grass, cassava bagasse, palm kernel cake and copra meal at 4.9, 9.8, 4.9 and 4.9 g DM/kg liveweight.day, respectively); and 3) a high cassava bagasse inclusion diet (elephant grass, cassava bagasse, palm kernel cake and copra meal at 4.9, 17.1, 1.2 and 1.2 g DM/kg liveweight.day, respectively). Intake and ADG were recorded. In the village experiment, 46 smallholder-managed Ongole crossbred bulls were randomly allocated to a control or intervention treatment group. Intervention group farmers fed their bulls 4 kg DM/day of the concentrate mix from the simplified feedlot diet in addition to normal feeding. Costs and returns, ADG and feeding were recorded. IOFC was calculated for both experiments and sensitivity-tested for variation in cattle price and opportunity cost of labour for harvesting home-grown feeds. In the pen experiment, the simplified feedlot diet yielded the highest ADG at 1.00 kg/day, with high cassava and elephant grass both yielding 0.23 kg/day. The purchased feed cost of gain was lowest for elephant grass (nil), followed by the simplified feedlot and the high cassava diets (9831 and 26,708 IDR/kg liveweight, respectively). However, the high ADG in the simplified feedlot diet made that the most profitable diet, wi