Looks normal. This is not parasite damage or rooster damage. Its a difference in their genes. Feathering rate in chicks is mainly controlled by the sex‑linked
K / k⁺ locus:
- K = slow‑feathering allele
- k⁺ = fast‑feathering allele
The 7 chicks mostly carry at least one copy of
K (slow‑feathering), while the other 17 are probably
k⁺k⁺ (fast‑feathering). Slow‑feathering birds take longer to feather out when their young. For example in my flock, the fast feathering girls have their juvenile feathers all done by 4-6 weeks of age while the slow feathering boys takes up to 10-12 weeks. This gene does not effect feather growth after maturity, so you won't see a delayed feathering for their future molts