Duck problem

Hi,
I'm writing here because I am so worried about my mulard duck. I'm Italian, so please, forgive my English.

I would like to have some advices about a recent problem my Perlino has. Eleven days ago, he started to be lethargic and he didn't walk so well. He didn't eat as always, and when he tried to stand up himself, his neck seems to "swing" around out of his body. I don't know how to explain it, his neck fluctuate strangely when he tried to run out of me. Besides, he couldn't poop easily.

I suspected an intestinal problem, because of my other duck that some years ago had same symptoms ( except neck thing ) . So, I gave him some antibiotics(Amoxicillin) and Betamethasone like my veterinary(he's not specialized in aviary) suggested me.
Besides I gave him "critical care" oxbow, as a emergency supplement.

Perlino started getting better after a week of treatment, he didn't eat easily grain and salads but he walked better and his neck wasn't bad as before. But, today my mother in law has found him in the same bad condition as eleven days ago( I'm out of town until the day after tomorrow ). I'm quite desperate because I really thought that he started getting better and solve his problem.
I told my mother in law to give him antibiotics and bethamesone again so she will treat him tomorrow.
Now, I'm asking you, have you ever had a problem like this? Do you know what it can be? How can I do? Please help me.

I forget to tell you that some days before the problem he ate soil, as other ducks. They eat it often when my parents in law hoe the ground around.

Thanks

I found this on another web page:

   "Since ducks love to splash around, if their water is not clean they could be exposed to something toxic. Mold or other toxic exposure can lead to symptoms of a sick duck such as lethargy, diarrhea, decreased appetite, loss of weight, seizures, dehydration, vomiting, drooping wings, unsteadiness on their feet, or difficulty walking."

https://www.cuteness.com/article/tell-have-sick-duck

I don't know much about ducks, we have chickens, but I would definitely separate the duck from its mates. If it is an infectious disease or bacteria you don't want to contaminate all.

Call your vet, if you don't have one, call your local vet clinic and ask for a reference of someone who treats ducks. I had a sick chicken once and the vet i contacted gave me a lot of free information on the phone.

I think that as far as home treatment goes, if you have already done antibiotics and it hasn't worked, you either need a vet consult with a simple alternative (if possible via phone) otherwise you might have to think about what you are willing to spend on a duck, as the vet could suggest expensive treatment.

I hope she pulls through... In bocca al lupo

Could it be Wry Neck? Pets4Homes (wry neck)

Does it look like this? The Farm Animal Sanctuary

Wry Neck
Wry neck is a condition that normally only affects ducklings. It can be fatal if not treated, since the ducklings is unable to hold its head up and will often not be able to walk correctly. Wry neck can be caused by a vitamin deficiency, blow to the head, or ingestion of toxins. Adding B1 and E vitamins, as well as selenium to the duckling’s diet can reverse the condition. You can supplement with vitamin capsules, or add some brewers yeast, bran, sunflower seeds or wheat germ to their diet or some herbs and spices such as parsley, sage, thyme, cinnamon, spinach, dandelion greens, alfalfa, marjoram or turmeric, which contain both Vitamin E and selenium.

copied from Backyard Poultry.

Wry Neck (sometimes called Crook Neck or Stargazing) is a condition that causes a chick or duckling (or sometimes a grown hen whose diet is nutritionally insufficient) to be unable to hold its head up on its own. The affliction can progress to the point that the little one walks backwards or tumbles over on its back, unable to walk at all. It can be fatal if not treated, as the chick or duckling risks becoming dehydrated and malnourished quickly if unable to eat or drink by itself.

from Fresh Eggs Daily.

Try an internet search for Wry neck/Torticollis photos.

I wish you luck.