AQUEBOGUE, N.Y. (AP) — Doug Corwin knew there was a problem at his family’s commercial duck farm in Long Island when he spotted scores of dead or lethargic birds during a barn inspection in January.

In a picturesque valley on the Southern Tablelands of New South Wales, maremma guardian dogs keep watch as thousands of white ducks waddle over grass and splash around in dams. Destined for the food ...