Chinese calender big and small month

I tell many stories, but not sure if I told this one publicly. My big sis's birthday is born on the 30th of the lunar year. I on the 29th. 

 Some years are small months, so there was no 30th. Rose would have her birthday on my birthday. So we only have one chicken slaughtered on that year. I was angry because I didn't understand slaughtering even one chicken was hard on my parents' budget.