hey folks. in the last 3 weeks I've lost 2 birds. a hen and a rooster. now i have a mallard hen acting the same. they are lethargic they sway their heads and as the disease progresses they start to fall over. i put the 1st 2 down thinking it was just coincidence. now I'm fearing this will kill my whole flock. there was no runny discharge or any other symptoms i could see. i hits very suddenly within 2 to 3 days the bird just stands or sits there and when it moves it head its like it loses its balance. i have 20 chickens 6 ducks and 2 geese. its not the food cause i feed high protein 20% and oyster shell plus treats of scratch and roaches i raise. these birds are all 2.5 yrs. old.