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I'm sorry to hear of this with Lili. Have you seen her feather pulling/plucking her chest? What does her diet currently consist of, please?
Thank you for the addfitional information. I like the idea of the fruit and vegetables but their protein intake needs to be improved for the best feather quality. Feathers are made mainly of the structural protein keratin. The Prestige food is a seed mix and we need to reduce the amount of seed in their diet. Seeds should compose less than 20% of their diet. A diet of mainly seed and nuts has excessive fat, carbohydrates, and phosphorus; marginal protein; adequate vitamin E, and are deficient in amino acids, calcium, available phosphorus, sodium, manganese, zinc, iron, vitamins A, D3 (necessary for efficient absorption of calcium), K, and B12, riboflavin, pantothenic acid, choline, and available niacin. Ideally, a balanced pelleted diet such as can be found here: www.harrisonsbirdfoods.com or here: www.lafeber.com/pet-birds should be fed as well as hard boiled egg yolk, pancakes and cornbread, the tops of fresh greens, dairy products such as yogurt and cheese, fresh fruits such as apples, pears, melon, kiwi, and berries, vegetables such as broccoli, carrots, beets, asparagus, cabbage, sweet potato, and squash, and even tiny pieces of meat.
Other considerations include bacterial (Staphylococcus, mainly), fungal, and viral infections (psittacine beak and feather disease/PBFD) which can be identified by testing by an avian vet (please see here: theparrotsocietyuk.org/veterinaryadvice/avian-vets)
Please respond with further questions or concerns if you wish.