The train, which was travelling between Settle and Carlisle, hit the animal shortly after 9.15am near Ribblehead.
The bull died as a result of the collision and the train suffered significant damage and has been removed from service.
At of midday, the line remains blocked and efforts are ongoing to remove the bull from the line.
All services from Leeds to Carlisle are suspended and rail replacement buses are in operation.
Northern customers are advised to check carefully before travelling on the route today and to all extra time for journeys.
Northern's regional director Tony Baxter said: “The remote location and nature of the incident means it has been difficult to get the line up and running again.
“We continue to work with colleagues from Network Rail to return services to the line as quickly as possible. I’d like to thank our customers in advance for their patience and understanding during this unusual incident.”