In the Táin Bó Cúailnge, the men of Ulster are disabled by a curse placed upon them by Macha to feel her labor pains in their hour of greatest need, thus disabling them when the army of Connacht attacks.
Cúchulainn is immune to the curse. I've understood that he is immune because he is a beardless youth, and so not affected by a curse affecting the men of Ulster. It may also be due to his demi-godhood, as a son of Lugh, the Long Arm.
In either case, Súaltam, Cúchulainn's human father, is neither a youth, nor is he descended from the Tuatha Dé Danann.
The translation from L. Winifred Faraday states specifically that Súaltam was unaffected:
A warning was sent from Fergus to the Ulstermen here, for friendship. They were now in the weakness, except Cúchulainn and his father Sualtaim.
And this version combining the translation efforts of Joseph Dunn and Ernst Windisch has an apparently unaffected Súaltam out grazing his horse with Cúchulainn when the warning from Fergus arrives, and Súaltam sets out for Emain Macha (in 6: March of the Host). This is after the curse is first said to have taken affect in 4: The Foretelling.
Related question: Why isn't Loeg disabled by Macha's curse?