For most beef producers, the final days of the last trimester of pregnancy for their cow herd is here. For some early-bird producers, calves are already bucking and jumping. Winters like this one are great and temporarily lay to rest all the discussion of when to calve. Often producers question when a particular cow is due. Most producers have a handy calving table that projects the calving date of the cow based on the day she was bred. For example, the "IRM Pocket Reference" guide shows a cow bred May 21 is due on calve on March 1. In recent years, the North Dakota State University Dickinson Research Extension Center has targeted March 1 as the start of the calving season. Do the cows begin calving on March 1? Unfortunately, the cows do not read tables. Basically, a cow will calve when she and her calf decide the time is right. We've all seen the old cow that gets up, lays down, gets up, lays down, walks over to the corner, walks back, lays down, twitches her tail and calves two weeks later. Or the cow with no udder that calves in what seems to be minutes and successfully producers a normal, well fed, day-old calf. A current trend is to advertise cows for sale with predicted calving dates. These dates were projected based on ultrasound measurements and are used to imply the cows or heifers should calf over a period of seven to 10 days. Establishing the age of a developing fetus with ultrasound is very accurate, but gestational age and calving date have little in common. At the center, ultrasound records help us sort cows based on 21-day reproductive cycles. No attempt is made to actually guess which day a cow is going to calve. In reviewing cow records, center research specialist Keith Helmuth complied all the cows with absolute breeding dates and sire of calf. In other words, 462 cows were artificially inseminated, and conceived to the unit of semen she was inseminated with. Because of the different breeds used, the parentage of the calf is not questionable. No DNA test or judge was needed to identify the father. Of these 462 cows, the average gestation length was 282.5 days. Of the 462 cows, only 87 actually calved on the expected date. These cows were expected to calve 283 days after breeding, on March 1st. In reality, the first live calf arrived February 11, then one on the 13th and one on the 16th. Three calves arrived on February 17, three on the 19th , one on the 20th, three on the 21st, nine on the 22nd, eight on the 23rd, and a rush on the 24th produced 17 calves. The calving crew is starting to sweat. On the 25th, 19 calves were born, 36 on the 26th, 38 on the 27th, 39 on the 28th and finally on the due date of March 1, 87 calves were born. More sweat, despite the cold weather. On March 2, 53 cows calve, on the 3rd, 25 calves, on the 4th, 16 calves, on the 5th, 22 calves, on the 6th, 20 calves, on the 7th, 15 calves, and on the 8th, only four calves. Just as there appeared to be a let up, on the 9th, 15 calves were born, on the 10th, 12 calves, and on the 11th, one calf. Finally, a slowdown, and the season finished with two calves on the 12th, three calves on the 13th, four calves on the 14th, and one calf each on the 15th, 16th and 17th. The last two calves were born on the 19th of March. All 462 cows conceived on the same day, but the calving season lasted 32 days. Approximately 80 percent calved within an 11-day window, 95 percent in a 19 day window, and 98 percent within a 28-day window.
If you want to bet me you know when your cow is going to calve, I'll bet you she won't calve on the day she's due. Cows don't calve in a seven to 10-day window, no matter who thinks they should. Happy calving. May you find all your ear tags! (Kris Ringwall is a North Dakota State University Extension Beef Specialist, Director of the NDSU Dickinson Research Center and Executive Director of the North Dakota Beef Cattle Improvement Association. He authors the Cow Herd Appraisal Performance System computer program that incorporates and analyses data collection from conception through consumption. He can be reached at 701-483-2045)
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