High temperatures and long photoperiods may reduce the potential of canola forage production in a system of early sowing. A field experiment was conducted in Matamoros, Coahuila, Mexico, during two growing seasons (2013‑2014 and 2014‑2015) to evaluate the response of six spring cultivars of canola (Brassica napus L. var. oleifera) to four early sowing dates (September 2 and 19; October 4 and 19). Chemical composition and yields of dry matter, crude protein and net energy for lactation were determined. Canola cultivars were affected by the growing seasons and sowing dates. The reduction of the environmental temperature and photoperiod, due to the delay in planting date, lengthened the canola cycle; which caused changes in the chemical composition of the forage and increases in dry matter and nutrients yield. The greater yields of dry matter (6036 to 8599 kg ha^-1), crude protein (1081 to 1308 kg ha^-1), and net energy for lactation (38209 to 45281 MJ ha^-1) occurred in the cultivars of IMC 205, Hyola 401 and Ortegon in the sowing dates of October 4 and 19. On the planting date of September 19, dry matter yield decreased by 18.5‑28.6%. However, crude protein and net energy for lactation yields were maintained among cultivars. Therefore, it was concluded that in the tested conditions the highest canola forage potential was obtained in early sowing when the crop was planted between September 19 and October 19. These results can serve as guideline for locations with similar climatic conditions.