Factors influencing time of parturition in range beef cattle.

A total of 2434 calving records from seven calving seasons were analyzed by the least-squares and chi-square procedures to study the influences of breeding group, age of dam, sex and birth weight of calf and dam weight at calving on the time of day of parturition. Frequency of day calving (0630 +/- 030 to 1900 h) was slightly but not significantly higher than night calving (1900 h to 630 +/- 030). The frequency of night calving was higher among heifers compared with the older cows. The cows which calved after May 15 (the last one third period of pregnancy) had higher frequency of day calving compared with those that calved earlier. The frequency of daytime calving was higher among the cows that weighed at most one standard deviation below the average compared to heavier cows of comparable age.