What are the main reasons backyard chicken brooding techniques fall short?

70% of the chicken deaths occurred during the brooding period. The main cause was inadequate insulation in the brooding house: when the chicks arrived, the room temperature was only 28 to 29 degrees; in some brooding houses the temperature fluctuated high and low, which lowered the flock's disease resistance and affected growth and development. In some cases, antibiotics and anticoccidial drugs were blindly added to the feed for a long time during the brooding period, which not only increased costs but also made bacteria and parasites develop drug resistance.