I don't see anything added to the beef or chicken, it's just the sausages. And salt, spices and whatnot added to flavour (not preserve) them can be given to chickens too - indeed, like all animals they need some salt in their diet.
If you want an authoritative answer, you have to look at an authoritative source. Search in the online free access academic journal Poultry Science for answers, rather than in the playground or the sewer.
https://www.sciencedirect.com/journal/poultry-science
anybody can write anything. Evaluate your sources to judge their reliability. Rubbish repeated is still rubbish. Give your references so your readers can evaluate them too.
Milk, cheese and other dairy is still missing from the list, despite Saysfaa pointing it out on page 1. Dairy is the most accessible, cheapest, easiest source of complete protein for chickens available. Don't take our word for it - try some with your chickens. And the comment about fat is...