How did Beltane bonfires traditionally protect cattle?

Traditionally, cattle were driven between the Beltane bonfires to protect them from disease and other harm. Early Irish descriptions say that ritual fires were kindled and livestock were passed between them at the beginning of summer.

The custom belongs to Beltane’s pastoral setting. Around 1 May, cattle were moved from winter holdings to summer grazing, making the festival an important moment for the health and safety of the herd. Fire, smoke and ashes were believed to possess protective powers, and the ceremony was intended to guard animals against plagues and supernatural danger.

In some places, cattle were driven around a single bonfire, over embers or flames, rather than strictly between two fires. People could also pass through the smoke or leap over the fire for luck. “Walked through flames” is therefore too extreme as the general answer: the established wording is that cattle were driven between the bonfires.