Many shepherds hold the view that the majority of lambings occur at night, particularly in the period just before dawn. Systematic studies of the timing of parturition in extensively managed ewes demonstrate a circadian pattern but reports differ with regard to the timing of peak incidence. Wallace (1949) found that peak incidence occurred between 00.00 and 04.00 hours confirming the traditional view. However George (1969) found that peak incidence for Dorset Horn ewes occurred during daylight hours.

Under intensive management ewes are typically housed in artificially illuminated pens for the entire lambing period and are under continual observation. The objective of the present study was to investigate diurnal variations in the timing of parturition in ewes under such conditions.