And still 136 bytes off 431:

  #define p printf 
  int main(){const char *g[]={"A Partridge in a Pear 
  Tree.\n","Two Turtle Doves, and","Three French Hens,","Four 
  Calling Birds,","Five Gold Rings,"," Geese-a-Lay"," Swans- 
  a-Swimm","t Maids-a-Milk","e Ladies Danc"," Lords-a-Leap"," 
  Pipers Pip","Twelve Drummers Drumm"};
  const char *d[{"First","Second","Third","Four","Fif","Six","Seven","Eigh","Nin","Ten","Eleven","Twelf"};for(int i=0,j;i<12;i++){p("On 
  the %s%s day of Christmas\nMy true love sent to 
  me\n",d[i],i>2?("th"):"");
  for(j=i;j>=0;j--){p("%s%s%s\n",j>4&&j<11? 
  d[j]:"",g[j],j>4?"ing,":"");}}}