5 week old runner acting sick

[Kimber21]

Hi, I have a 5 week old runner duck that hasn't been acting himself for the last couple of days. He doesn't have much energy but will go swimming. He drinks okay but isn't eating very much, he does take some bites tho. He has green runny poop. I've been feeding them masterfeed duck starter and adding in oats and nutritional yeast. He also walks hunched over. My other ducks (1 call duck that is almost 8 weeks and 3 other runner ducks. I tried giving him peas yesterday but he didn't want them.

 

[Miss Lydia]

Hi and so sorry we didn’t reply. How is your duckling?

 

[Pollo Blanco]

What kind of oats?