I love the fact that you can customise your farm in Harvest Moon to give names to all of your animals at birth. With names, your animals, especially the cows and sheep, become like friends that you greet each day by name. I have not sold any animals yet in Boy and Girl, but in Innocent life, when you sold an animal, you were asked "If you sell Daisy the cow, you will never see her again, are you sure you want to continue?" This almost had me in tears the first time I read it, and I didn't go through with the sale! However in Innocent Life, you did not have the option to give your animals personal names, instead you had to choose one from a list. Being a vegetarian, and an animal lover, I love this aspect of Harvest Moon.
In Boy & Girl I have personalized my animals in the following way:
Farm: HipPiTy farm
Horse: PIkwIk *
Sheep: ShaWn, WooLard*, YarNaRd*, LaMbERt*, BaaBAra*, FleeCi**
Cows: TriXsY, DikXi *, LiKxI **, PiKxi **, FiKxi **, WiKxi **, RiKxi **, BiKxi **
Chickens: ChuCki, CLuk*, CHooKi, CheePa, KliKi *, ChUkXI *, ChIkXi *, ChUnKi *, RooSta *, HeNRi **