HOURLY DISTRIBUTION OF TIME OF PARTURITION IN BEEF COWS

Abstract

Data on 1151 calvings recorded over a 4-yr period at the Agriculture Canada Research Station, Brandon, Manitoba were analyzed to examine the influence of various factors on the time of day of calving of beef cows. Factors examined were year of calving, sex of calf, age of cow, weight of cow, calf birth weight and breed type. The hourly distribution of calvings was relatively uniform over the 24-h period. Slightly more calves were born from 0700 h to 1900 h (51.5%) than between 1900 h and 0700 h. Breed of maternal grandsire and of maternal granddam were the only factors that appeared to influence the time of parturition. Percentages of calves born during the day (0700–1900 h) having Hereford, Charolais, Simmental and Limousin grandsires were 59.0, 54.2, 51.0 and 45.6, respectively, whereas 55.9, 55.6 and 41.0% of the calves from Hereford, Angus and Shorthorn granddams, respectively, were born during the day. The hourly distribution of 212 potentially abnormal calvings was significantly uneven. The highest incidence of abnormal calving occurred from 1100 h to 1500 h (22.2%) and the lowest from 2300 h to 0300 h (12.1%). Key words: Beef cows, parturition, hourly distribution