I just bought eight ducks- three Silver Appleyard hens and a Silver Appleyard drake and four young female Golden 300s. They are free range in the day, locked in a coop at night. They share about 1.5 acres of pasture with four goats. Its kind of scruby pasture- the outside is ringed with blackberries and the inside is kind of overgrown. I'm in SW Washington, so they will get a decent amount of forage year round except for maybe a month or two . I have grand plans to plant fodder for them next summer, but right now I'm feeding them duck and geese ration from the local coop. They get some whey and wizened carrots/ apples/ etc with their food. They all seem to be good active foragers. So how much pellet food should I give them a day? Right now I'm giving them about 6 cups- about 5oz. per duck per day. I'm going off the recommendations I found on the internet of 4-6 oz a day per duck, but that estimate seemed to be coming from people with a more confined space. My Silver Appleyards are already a bit on the chunky side, and I don't want to overfeed them.
General advice is to give them as much as they will eat in around 10-15 minutes, if there is any left over then give less next time. My 3 muscovy ducks live with 7 chickens, and they get around 4-5 cups of grain/concentrate per day between them, they also free-range although that stops today as winter is now here. I don't believe they will overeat.
I hope I haven't missed the point.... your question Anna was how much to feed your "pastured" ducks.
We have a small flock of 4 chickens, 7 Indian Runner ducks (2m 5f) and a breeding quartet of geese. They free range all day in all weathers from sun-up to dusk and get no feed or water in their coop/houses overnight unless there are chicklings, ducklings or goslings around, when we put small water and feed trays down for them and the mommas.
I have to admit, I can't imagine trying to time them eating ("as much as they will eat in around 10-15 minutes")... but maybe because we never trained them to food they are so adhoc in their feeding habits.
For the geese and ducks we only put down "hard feed" from April (after the last frost) until November (around the first frost). And that is about 2kg of unmilled wheat grain, split between 2 troughs and covered with water. We get that (untreated of course) for around 4 euros for 20kg sack. That feed is all gone by the time they go to bed. We also have a large chicken feeder that gets filled up every 3-4 days with a locally milled (no additives) mixture of oats, barley, wheat, rape and maize - the same mix that we use for our pigs. That's all year round mainly for the chickens, we buy that in at about 3 euros for 20kg. The ducks occasionally will pick at that but not very much.
So what else do they eat...
We have maggot buckets out as soon as it warms up and they fight (nicely) with the chooks to get the grubs from that
We put down old hay or straw bales as well as large logs and periodically lift/move them to give the chooks and ducks access to grubs and insecty critters underneath
The ducks do a lot of snail and slug hunting (we have a lot of snails around our place)
We get loads of un-saleable fruit and veg during the year from a local market garden and that gets all chopped up for the birds (oh and the pigs of course)
As with the chooks, the ducks will happily gobble up minced/finely chopped raw meat/bacon rind
In the depths of winter, maybe once a week, we give the ducks and chickens a treat of a 2kg bag of (defrosted but uncooked) fish - whole small fish like sprats, sardines, whitebait - which they really devour with relish
I never realised how well our ducks can dig and burrow into the bottom of bales of straw/hay/alfalfa to try and find the bugs underneath. They also regularly work through the pigs wallows digging and sieving through the mud for whatever is there for them.
We get 5 eggs most days from our ducks, they are prolific and have been laying all winter despite regular temperatures of -5C to -10C. Even now in about 50cm of snow around their house we are getting 3 or 4 eggs per day.
Good luck with your birds! We really enjoy ours. I've attached a few pictures of our poultry too just for fun :-)