Many producers try to time their spring or fall breeding seasons so the calves arrive at the optimum time. Brett Barham, University of Arkansas professor of animal science specializing in beef cattle breeding and genetics, noted while the official gestation period for cattle is 283 days, individual animals can vary by a week or two. “Typically, the calving season probably needs to be dictated around available forage for the cow while she’s at peak lactation,” Barham told Ozarks Farm & Neighbor. “We have spring calvers and fall calvers, and those calving seasons should be set up to have those calves about 30-60 days old during peak forage production.”
There are still a lot of ranchers in the Ozarks, Barham said, who don’t have a distinct calving season; he believes many of them would benefit from having a controlled calving season of 90 or even 60 days. “If the cows are in good shape where they’re actively cycling when you turn the bulls in, 60 days should be plenty of time to get 90-95 percent of those bred,” he said. Although there’s not much of an advantage of a 90-day season over 60 days from a pregnancy rate standpoint, Barham pointed out for cows that are questionable on their nutritional status, a longer calving season gives them one more estrus cycle to go through and an extra chance to get bred.
Some producers balk at moving to a controlled season for fear it will leave them with too many open cows, but Barham said the move can be a gradual one. “We’ve had a lot of success  working with producers over a 3-4 year period most of the time; some of them take 5 years to slowly bring that calving season down to a 90-day period, or shorter if that’s what their goal is, with very few open cows due to that process,” he said.
Many of those who already have a controlled season breed their cows in the summer so they’ll calve in March or April. “A lot of people with spring calvers don’t really want to calve in January and February because it’s a little cold for some people here,” Barham said, “even though a lot of people in Montana and places like that don’t have any problem calving in the cold weather.”
That may not be optimal, according to Eldon Cole, University of Missouri southwest region extension livestock specialist at Mt. Vernon, Mo. He told OFN that while February and March calving “is very risky weather-wise, we’ve found that those cows that are bred in early summer in this part of the country do settle easier and maintain that pregnancy better.” If you want the calves born in April, the cows have to be bred in much hotter weather, which Cole said is injurious to conception rates.
Many producers have turned to a fall calving season; Cole said one of the biggest reasons for that is calving weather – cows bred around Thanksgiving will deliver in late August or early September. “Normally, this is a pretty good time of the year to calve,” he said. “The cow has plenty of green grass to help her in her early milk production phase, when she starts to nurse that calf.”
Of course, that wasn’t the case for many producers this year due to the drought.  But the hope, Cole said, is that the rains will come. “Usually those cows that are calving this time of the year will be in good, fleshy condition,” he said. “They’re healthy and strong, and will start cycling back for rebreeding fairly soon.” It’s a critical decision for the producer when to turn the bull in again; if you breed the cows back in early fall, the calves will arrive in July, when the weather is dry and hot.
And the heat does play a factor in gestation. “The hotter the weather, the earlier calves tend to come,” he said. “As a result, with this year’s heat wave, people who thought they were going to get calves in September started getting them in mid-August.” In addition, producers can study gestation length EPDs, which will tell them which of two sires’ progeny will have the longer gestation length.
Producers may wish to manipulate this data when they make their breeding decisions. Cole pointed out people who show cattle may need their calves to be born by a certain date, and may try to adjust the breeding season and the potential for an early delivery accordingly. But you’re still gambling; chuckling, Cole observed, “Sometimes those cows don’t read what the book says they’re supposed to do when they calve, and they will calve several days off one way or the other. You can have cows that are all AI’d the same day, to the same bull, and yet may calve 14 days apart.”


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