The problem with offering a mix free choice is that some birds may be eating primarily dog food, some may be eating the sweet feed, and some get mostly starter. Dry dog food is ok for most dogs- not a good primary chicken diet. Sweet feed is extra calories (grains and molasses) for horses/goats ect- but not balanced for a chicken. Start is low in calcium. Many roosters do just fine eating primarily layer ration, too much calcium is hard on the kidneys, not really an issue with the liver. If your girls are eating primarily the sweet feed- they could have a fatty liver.
They are old enough that the distended abdomen could be tumor(s) (viral or primary reproductive), ascites due to heart disease or liver failure, yolk peritonitis. Nothing very good here. If it is liver disease due to unbalanced diet- that may be helped with a radical diet change. Egg yolk peritonitis can be helped sometimes with antibiotics- short term, but long term is typically fatal. If you can seek veterinary help from someone who knows chickens- that would be ideal- if these are pets. If you are looking for hens that will lay and be healthy long term- these girls sadly, are not good prospects.
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