Rather than being a conventional poem this is referred to as an Extempore. This is believed to have been delivered by Burns at one of the many dinners without previous composition
O thou who kindly dost provide
For every creature's want!
We bless Thee, God of Nature wide,
For all Thy goodness lent:
And if it please Thee, Heavenly Guide,
May never worse be sent;
But, whether granted, or denied,
Lord, bless us with content. Amen!