Corn silage (CS) is widely used on dairy farms because of its high yields and energy content. Sweet pearl millet (SPM) and sweet sorghum (SS) are forages that can produce yields similar to CS, but with lower N needs. The aim of this study was to evaluate the economic and environmental differences of CS substitution by SPM or SS through simulations with the whole-farm model N-CyCLES. Three virtual farms were built in the model for contrasted climate and agricultural regions (Maritimes: 63 cows and 513 584 kg/yr, Québec/Ontario: 71 cows and 613 841 kg/yr, and Prairies: 144 cows and 1 212 875 kg/yr). The model was adjusted for crop growth and rotations, fertilization needs, and constraints specific to each virtual farm type. The SPM was evaluated as a replacement for CS in the 3 climate regions, whereas SS was tested for Québec/Ontario, the only region with the appropriate climate for this plant. Results show that replacing CS for SPM and SS caused a slight decrease in net income per kg of FPCM (−7% in average). Environmentally, replacing CS for SPS and SS reduced greenhouse gas emissions per kg of FPCM (−4% on average), increased P balances (+93% on average), but lowered N balances for 2 out of 3 regions (−9% on average). These results suggest that, although CS is a good option, its substitution by SPM or SS is a viable alternative for Canadian dairy production. Table 1. Farm economic and environmental impacts of forage type

	Maritimes			Quebec/Ontario				Prairies
	CS	SPM		CS	SPM	SS		CS		SPM
Dairy farm profit ($/kg FPCM1)
Net income	0.10	0.08		0.21	0.20	0.20		0.22		0.22
Crop income	0.03	0.04		0.09	0.06	0.06		0.01		0.01
Greenhouse gas emission (kg CO2 eq./kg FPCM)
Total	1.39	1.37		1.32	1.29	1.30		1.37		1.34
Milk allocation	1.10	1.09		0.99	1.00	1.01		1.08		1.05
Cash crop allocation	0.06	0.06		0.13	0.09	0.09		0.01		0.02
Mineral balance (g/kg FPCM)
N	12.5	10.92		13.36	11.71	12.4		14.5		13.44
P	1.86	2.70		0.36	0.89	0.77		1.20		2.03

¹Fat- and protein-corrected milk.