Muscovy duck question

I used to have 55 muscovy ducks back in the '90's. Some of them got sick and died and I never could find out what caused this. Called all the vets and any medical place I could find to call. (No internet back then). Anyway, I thought if I posted what happened to them someone on here would know what it was. The first day they were sick they would stand and drink nothing but water and they would stand right at the water dish. The second day they would sit there drinking nothing but water. By the third day no more water and they would sit there while their head would weave back and forth and by afternoon they were dead. This happened mostly to the males. One time I did put corn syrup and chicken broth in the water and that night the duck threw up a lot of corn. Just kept throwing it up and then he was fine but then a month later he got sick again and died the next day. Never made it the three days. Between them getting sick without me able to help I could not see letting them hatch anymore. So, does anyone know what caused them to be sick? They were all pets too.