A few of my 8 month old ducks are a little thin. (One of whom was at the vet not long ago). What is some healthy food (either duck feed or fruit/veg) that can help them put on a little healthy weight? They have 24 hour access to duck pellets (Purina) and they also get peas and black soldier fly larva as treats in the evening. They are also free ranged for an hour or 2 a day.
They have all been laying a lot of eggs so I think they need more nutrients.
Personally, unless your ducks are emaciated/very underweight, or your avian vet has expressed that they should gain weight, I wouldn't be concerned. My own ducks have always been on the thin side, and I have discussed this at length with my avian veterinarian. You can weigh the smaller individuals to see if they are loosing weight over time, that could be another concern.
Have you palpated their breasts next to their keel bone to assess their condition?
Since you are concerned about the nutrition lost during egg production, what about feeding their own eggs back to them? Also, when the days grow shorter I recommend allowing them to have a natural daylight schedule, so their bodies can take a break. So, no night lights or porch lights.
Aside from foraging I would be concerned with excessive amounts of treats contributing to an incomplete nutritional profile. Most healthy treat foods that ducks seem to love, like lettuce and tomatoes, are low on calories. And most unhealthy treat foods that are higher in calories, like bread or white rice, are empty of nutrition. I have heard of some members giving fish cat food to ducks, but it is formulated to meet the nutritional needs of cats, not ducks, and should be fed as a treat.
