Heart rate and laying behavior in two strains of domestic chicken

The heart rates of caged hens, from two strains of domestic chicken (Gallus gallus domesticus), during the 20 min before and after oviposition were studied. Heart rates were measured using subcutaneously implanted radiotelemetry devices. In one strain, heart rate was low and relatively constant before laying, increased sharply at the moment of laying, and then decreased gradually during the post-laying period. Hens from this strain exhibited sitting behavior before laying. In contrast, in the other strain, heart rates increased steadily during the pre-laying period, peaked sharply at the moment of laying, and then declined during the post-laying period. Hens from this strain exhibited restless pacing behavior before laying.