Question:  query regarding some broiler showing  decrease growth after proper feeding 
Answer:  told im to give growth promoter[ sharkoferol ] at the age of 12-16 days / vitamin b complex 10 ml / 100 birds/ select the alert pullet at the time of collection from wholesaller / retailer  / provide good feed & liver tonic from time to time , some genetic cause is responsible for decrease growth   decrease basel metabolic rate [ bmr] & feed conversion ratio is different for different birds