Two cattle were killed when they were hit by the Cork to Heuston around 7pm on Wednesday.
The train came to halt just north of Limerick Junction and this caused knock-on delays for several hours.
The two cattle managed to break out of the field they were in and enter a wooded area owned by Coillte.
From there, the cows wandered on to the track where the Cork-Heuston train collided with them.
Irish Rail confirmed the cattle were killed in the incident.
The collision with the animals caused a major mechanical problem inside the train, resulting in the 17:25 train from Cork to Heston being delayed by five hours.
It caused knock-on delays for other trains, some of which had to be re-routed.
No people were injured in the collision.
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Significant delays after train strikes a herd of cattle