Drag down not working for drop down list once sheet is protected

Hello, I have an intermediate knowledge of Excel but am having issues with using the drag down in a drop down list once I have protected the sheet.

Before I protect the sheet, you can select from the drop down list in one cell and then drag this down to the below cells. You can see this in the attachment "Animal Form" in columns labelled 1 through to 5.

However, when I protect the sheet this option is no longer available. See attachment "Animal Form - protected". You can use Ctrl D to fill the cells but would prefer the drag down option.

Does anyone have a fix for this?

Thank you.