For Holy Nativity on Saturday, we didn't sing the usual antiphons (Psalms 102 & 145 and the Beatitutdes). Instead, the choir sang some verses, and we responded each time with, 'Through the prayers of the Theotokos, save us, O Saviour!'. Then a later one was similar, but the response each time was the troparion for the Nativity, (Thy Nativity, O Christ God, hath shined upon the world the light of knowledge, &c.)
Also, we omited the Trisagion.
Is this usual on Feast Days, and, if so, is there one special set of antiphons for Feast Days or do they vary?
I'd be very pleased to find out more.
Many thanks.