Predicting the time of calving

Scientists recorded data on 5 consecutive years in a herd of spring calving crossbred cows at the Kansas State University Agricultural Research Center at Hays, Kansas. They recorded the time of calving (to within the nearest one-half hour). Births that could not be estimated within an hour of occurrence were excluded. Cows were fed forage sorghum hay daily between 4:00 and 6:00 pm. For statistical purposes, the day was divided into four-hour periods.

Between 6:00 and 10:00 am, 34.23% of the calves were born;
Between 10:00 am and 2:00 pm, 21.23% of the calves were born;
Between 2:00 and 6:00 pm 29.83% of the calves were born;
Between 6:00 and 10:00 pm, 8.41% of the calves were born;
Between 10:00 pm and 2:00 am, 4.4% of the calves were born; and
Between 2:00 am and 6 am, 1.91% of the calves were born.

It is interesting to note that 85.28% of the calves were born between 6:00 am. and 6:00 pm.

These data also revealed that for a majority of a animals in the herd, the time of calving was within 3 hours of the average time of day that cow had previously given birth. Feeding the forage in the early evening hours undoubtedly influenced the percentage of cows calving in daylight hours. Source: Jaeger and co-workers. Abstracts 2002 Western Section of American Society of Animal Science.