Powershell, 487 453
0..11 | % {
'On the {0} day of christmas my true love gave to me {1}`n'-f
(
'first^second^third^fourth^fifth^sixth^seventh^eighth^ninth^tenth^eleventh^twelfth'.Split('^')[$_],
(
'a partridge in a pear tree^two turtle doves and^three french hens^four calling birds^five golden rings^six geese-a-laying^Seven swans-a-swimming^Eight maids-a-milking^Nine ladies dancing^Ten lords-a-leaping^Eleven pipers piping^Twelve drummers drumming'.Split('^')[$_..0]-join' '
)
)
}
Thank you to Daan for the idea of splitting a concatenated string.
I had originally included a switching statement to get the "and" on the partridge for all but the first verse. But, because the question absolves us of punctuation, we can just append the "and" to the doves.
This results in line feeds as follows:
On the first day of christmas my true love gave to me a partridge in a pear tree
On the second day of christmas my true love gave to me two turtle doves and a partridge in a pear tree
On the third day of christmas my true love gave to me three french hens two turtle doves and a partridge in a pear tree
