REMOVAL OF RESIDUAL YOLK AT HATCH INFLUENCES FOOD CHOICE AND FEEDING-ACTIVITY IN LINES OF CHICKENS SELECTED FOR HIGH OR LOW JUVENILE BODY-WEIGHT

The effect of residual yolk removal at hatch on growth and feeding beh avior was assessed in lines of chickens divergently selected for low ( LW) or high (HW) 56-day body weight. At hatch chicks were assigned to 1 treatment: removal of the residual yolk (R) or no surgery (I). Twent y-four chicks per line (12 I and 12 R) were assigned to an all-mash re gimen (M) and 48 per line (24 I and 24 R) to a choice (C) between mash and dietary residual yolk. HW were heavier than LW chicks regardless of treatment. On day 5 and thereafter, chicks given a choice were heav ier than those eating mash. HW chicks ate more than LW ones. The perce ntage of yolk eaten increased during the 2-3 d after hatch, remained c onstant for 2 d, then decreased. Results are discussed in term of yolk need and development of the gastrointestinal tract in the divergent l ines.