I've got a strong healthy flock of 21 birds. All between 18 and 20 weeks of age. We've had 1 barred rock that we've noticed is significantly under developed. No waddle, no comb, very pale. She had pretty much always been on the smaller side. Just today while they were all free ranging, I've noticed her moving very slow, huddling next to the coop wall, not interacting with the other birds. No scratching or foraging. PS: the birds were all vaccinated for mareks. Any thoughts? Suggestions? ??