A trip to Canterlot for Derpy and Berry is clearly a great way to destress, recharge those batteries before going back to raising their kids. But will Derpy even make it to Canterlot without making a nuisance of her huge boobs and endless lactation?

Derpy goes to Barnyard Bargains with her family. She shares her milk with an employee, then later makes a pretty public spectacle of herself.

For peace of mind and possibly to find interested parties, Derpy decides to have her exceedingly milky breasts checked at the Ponyville Hospital

Derpy hasn't stopped producing milk even weeks after she stopped nursing her kid. During a bit of experimentation in the presence of her best friend, Derpy discovers the awesome powers of her rack.