A large number of poults from a line (E) selected long-term for increased egg production were observed, in recent generations, to flip over during the week immediately after hatching. This condition, termed early poult flip-overs (EPF), is characterized by the poults falling on their back and being unable to right themselves without assistance. Poults that flip over more than once appear to lack neurological control, lying on their backs with their legs paddling. If handled, the affected poult moves its head laterally and after several seconds appears to go to sleep. When placed on litter, the poult has no sense of balance and falls to one side or the other and starts paddling its feet. Poults that flip over may also chirp loudly. Observations from previous years indicate that no bacterial infectious agent was associated with the EPF condition. Affected poults have increased mortality relative to normal poults that do not flip over. The objective of the present study was to evaluate the effects of inheritance, beak trimming, hatching time, genetic growth potential, and poult hydration on the incidence of EPF. The E line had a greater incidence of EPF than its randombred control line, indicating the possibility of a genetic basis for the condition. However, within the E line, the heritability, based on variation among full-sib families, of the occurrence of EPF (assuming that EPF is an all-or-none trait) was low, being 0.044 and 0.052 in 2 consecutive yr. The heritability of the number of days (out of five) a poult continued to flip over was somewhat higher [0.26+/-0.002 (SE)]. Genetic growth potential may influence incidence of EPF for, when the E line was crossed with a large-bodied experimental line selected for increased 16-wk BW, the frequency of EPF was reduced and BW at 13 d of age was increased in the cross relative to the pure E line even though poult weight was similar at hatching in the two genetic groups. In the E line, later hatching poults within a hatch had a greater incidence of EPF than those hatching earlier. Neither beak trimming with an electronic beak trimmer nor poult hydration influenced EPF.
