The New York Times has an interview with an alpaca farmer who lives on Martha's Vineyard and who asserts, "Alpacas are a federally recognized livestock, so owning them has tax benefits."
The Times doesn't press the issue, but why the tax code should incentivize someone to open an alpaca farm on Martha's Vineyard (or anywhere else, for that matter) is a fine public policy question that you'd think might be asked by some non-farmers.