Are you feeding medicated crumbles? You don't have to feed them a regiment for eight weeks just cut a portion of it in with your regular feed. I deal with hundreds of chicks every year ( micro-farm layer operation) and the regiment I use is designed around imprinting the natural defenses for my local "coop flora". Since you've been doing this for a couple of years it may be time to super-clean the coop and run. It looks like whatever over ran your chick may still be a vector or mutated cocci strain. Although, another consideration was that the chick was terminal when you received it. Here is my basic schedule for chicks through week 18:
Arrival
Beak dip, peep (sound strength) check, and visual inspection.
Water with probiotic and electrolytes and medicated crumbles.
First 24-72 hours
Monitor and motility tests every six hours. Remove and quarantine any slow movers.
Water with probiotic and electrolytes and medicated crumbles. (water changed daily)
Brooder area cleaned weekly with complete removal and replacement of bedding (river sand)
Week 2
Close monitoring of activity. Listening is important as weak peep can indicate trouble.
Well water and regular start and grow chick feed.
This is where I let the local flora 'imprint'. This allows my local flora to build in their guts and their immune system to develop and balance the symbiosis.
Week 3
Close monitoring of activity.
Well water and 1:1 medicated/regular mix.
I'm now inspecting the droppings for color, consistency and worms. If they were getting overwhelmed the medicated will help them clear it while bolstering their own immunity.
Week 4
Close monitoring of activity.
Well water and regular chick feed and Scratch wild bird seed mix (reallly small seeds from a variety of plants).
By now the chicks are eating straw, bugs, and scratch.
With this regiment I've maintained a 99.99999992 survivability of 100-200 chicks in the cycle. If you work in technology, this a better rate than the up-time or availability of Google. Uncannily I always lose a chick at week 4. Having seen how quickly they grow I write this off to a genetic defect (heart or lung failure etc).
Week 5-6
Close monitoring of activity.
Well water and regular chick feed, Scratch grains (barley, corn) and anything except meat from table scraps.
Depending on weather this is when they get punted from the brooder area to the big house. This is also where feather eating and other bored induced destructive behaviors happen. I raise BSLs and BAs and the BSL feather developement is slower so the pin feathers become enticing targets for the BA's. I have a separated group of ten now (Clan of the Crooked Feathers) that is catching up to the main group but it is clear after separating them they are developmentally slower than the main group by about two weeks.
Week 7
Close monitoring of activity.
Well water and regular chick feed, Scratch grains (barley, corn) and anything except meat from table scraps.
Week 8
Close monitoring of activity.
Well water and 1:3 mix of medicated to regular. Scratch grains (barley, corn) and anything except meat from table scraps.
Week 9-12
Operational monitoring of activity.
Well water and regular chick feed, Scratch grains (barley, corn) and anything except meat from table scraps.
Week 13-17
Operational monitoring of activity.
Well water and 3:1 regular chick feed with adult layer feed, Scratch grains (barley, corn) and anything except meat from table scraps.
Yes I break mfgs recommendations because I understand there is a profit motive for feed companies and their "feed plans". If you read the required Federal white tag on your feed products it details the composition of the feed. A comparison will show you what you are getting and losing between the feeds. I'm also hoping to kick-start the egg production through key nutrient intake in much the same way an abundance of fast food induces puberty earlier and earlier in female humans.
Week 18
Operational monitoring of activity.
Well water and 1:4 medicated chick feed with adult layer ration, Scratch grains (barley, corn) and anything except meat from table scraps.
This is the last flock distribution of medicated feed. By now they should have consumed most of indiginous insects and the local cocci flora is imprinted and the chicks immunity properly set. Rarely, if at all after this regiment will I have to individually medicate for cocci, your mileage may vary depending on hundreds of other variables. After that everything is situational and weather triggered. With all that said, sickness possibly indicates some biological vector out of control in your environment. Eradication is impossible but knocking it down so it is manageable is the key. Hope this helps!
Note: I live 6300' in the high desert. Everything exposed to the sun or air is immediately immolated or dessicated and at less than 20% humidity, microbial vectors really, really, really struggle here. So much so that we abandoned outdoor gardening for hydroponics. Less wind, critters and sun.
