Predicting time of calving
One of the advantages of fall-calving compared to spring (late winter) calving is the pleasant weather that the cow/calf operator finds at 2:00 AM when he or she goes out to check the heifers. The downside of fall calving is the fact that these cows and heifers are not being fed from the truck or hay feeder.
In most years, they are getting plenty of nutrition from the standing forage in the pasture. Therefore, the rancher will have less influence on the time of day that the cow goes into labor. As has been documented many times, if the cows are fed late in the day, a higher percentage of calves will come during daylight hours.
Very precise records about the previous history of adult cows may give some help to that portion of the herd. Oregon State and Utah State universities conducted an interesting study to determine whether individual beef cows display a repeatable pattern of calving time from year to year. Cows in this study ranged from 3 to 7 years of age and the number of calvings per cow ranged from 2 to 5, resulting in 523 parturitions for 201 individual cows. This data was gathered in late winter/ spring calving seasons which began in late January and ended in late April. Cows were fed each day in late afternoon. Days were divided into six periods of four hours each. The percentage of cows calving within each period was: 6 AM-10 AM, 34.2 percent; 10 AM–2 PM, 21.2 percent; 2 PM–6 PM, 29.8 percent; 6 PM–10 PM, 8.4 percent; 10 PM–2 AM, 4.4 percent; and 2 AM–6 AM, 1.9 percent. By feeding late in the day, 85.2 percent of the calves came between 6 AM and 6 PM. Average time of day of calving was determined for each cow. The difference between the individual’s average and her calving time for each year was then calculated. The average difference for all cows was plus/minus 2.65 hours.
Statistical analysis confirmed the average difference was significantly less than three hours. These results indicated that for this herd of cows, which was fed in late afternoon, the time that calving will occur may be predicted within about two to three hours based on the average time of day that a cow had previously calved. — Glenn Selk, Oklahoma State University Extension Cattle Reproduction Specialist