Supervision plays an important role in successful calving, particularly for first-calf heifers, says Oklahoma State University Extension Cattle Reproduction Specialist Glenn Selk. But the availability of personnel to observe and assist declines considerably when heifers or cows give birth in the middle of the night.

The easiest and most practical method of inhibiting nighttime calving, he says, is by feeding cows during the night. The specific mechanism for this relationship is unclear, but Dr. Selk sites hormonal effects and increased intraruminal pressure after feeding as possible explanations.

Several research trials have demonstrated the relationship, including one in Iowa in which researchers fed 1,331 cows on 15 farms once daily at dusk. In this study, 85 percent of the calves were born between 6:00 a.m. and 6:00 p.m. Whether cows were started on the night feeding the week before calving started in the herd or two to three weeks earlier made no apparent difference in calving time.

Dr. Selk notes that on many large ranches it is physically impossible to feed all of the cows after 5:00 p.m. In those instances, he suggests that ranch managers plan to feed mature cows earlier in the day, and concentrate on feeding first-calf heifers at dusk since those are the animals most likely to need assistance.