This section contains two versions of the same leg of the journey, from Cuailnge to Conaille Plain. In the first version, the armies divide at Finnabair and lay waste to the country but cannot find the bull. Lóthar tells Medb the Brown Bull is in Dubchoire, and the army pursues him there, but he attacks the camp, killing Lóthar and vanishing. They continue to search for the bull, attempting to cross the river Cronn and losing a famous warrior named Ualu. Many others were killed at this spot (although it is unclear if the narrative refers to later deaths or in the present), including two chroniclers of The Táin, Roan and Roae, and 124 kings. Finding the source of the river, the army crosses the mountain-summit; Medb marks their crossing as an insult to Ulster by creating a gap at Bernas Bó Cuailnge. They attempt multiple river crossings, many of which sweep away their charioteers and warriors.

In the second version of this journey the armies divide at Finnabair, with Ailill leading one part, and Fergus and Medb leading the other. Medb here cuts the gap at Bernas Bó Ulad so their cattle can pass over the mountain.