Ducks have different nutritional needs than cats, so feeding cat food, even cutting with greens is not the best choice for their long term needs.
They really need feed. Chicken feed at 16% is fine. All purpose at 16 to 18% is better, but harder to find. The supplements you are seeing is what makes the feed better for them.
Oyster shell should be offered separately so the ducks can eat it as their body needs. It is not the same as grit. You can offer grit, but if they are out in the yard free ranging they usually pick up what they need in the yard.
When you give veggies that are hard, they may not eat them. But they are more likely to if it is small enough not to choke them when they swallow it. Remember they have no teeth and cannot peck things apart like a chicken due to their rounded bills. They swallow things whole. My neighbor had a duck choke to death on a huge banana slug. Worms should be a treat, not a staple. I like to go and turn over dirt in the garden with ducks climbing all over my feet. But it is not for their daily meal.
They really need feed. Chicken feed at 16% is fine. All purpose at 16 to 18% is better, but harder to find. The supplements you are seeing is what makes the feed better for them.
Oyster shell should be offered separately so the ducks can eat it as their body needs. It is not the same as grit. You can offer grit, but if they are out in the yard free ranging they usually pick up what they need in the yard.
When you give veggies that are hard, they may not eat them. But they are more likely to if it is small enough not to choke them when they swallow it. Remember they have no teeth and cannot peck things apart like a chicken due to their rounded bills. They swallow things whole. My neighbor had a duck choke to death on a huge banana slug. Worms should be a treat, not a staple. I like to go and turn over dirt in the garden with ducks climbing all over my feet. But it is not for their daily meal.