by: Heather Smith Thomas

Most beef producers routinely have their cows checked for pregnancy after the breeding season. This is an effective tool to help determine which cows to keep and which ones to sell. Jeff Hoffman, a veterinarian near Salmon, Idaho, says the biggest reason to know which cows are open is that it's a major cost to feed them through winter, and this feed cost is a waste of money if they are not going to have a calf. You may want to sell them in early fall when prices are good, and in some cases (if they are too thin to bring a good price), you may choose to fatten them and sell them later in the winter for more money.

“The other major reason to pregnancy test is that finding more than a typical number of open cows can alert you to a disease problem,” he says. There are a number of diseases, including trichomoniasis, vibriosis, IBR, BVD, etc. that may cause cows to lose their pregnancies. Typically the sexually transmitted diseases like trich and vibrio cause early abortion and the cow returns to heat, ending up open or calving very late. If bulls are left with the cows all summer, some of these cows may become pregnant again. Finding out that you have a bunch of open or late cows is a little bit after the fact, but at least you'll know there's a problem and can take measures to correct it.

“Nutritional deficiencies in the herd may also show up as open cows, especially in the younger cattle and mainly in the second calvers. Most people feed their yearling heifers adequately and they breed up fairly well—but they are not raising a calf,” says Hoffman. The two year olds with calves at side are still growing, plus trying to feed their calf. That's the age group that may end up with a high percentage open.

Part of the reason is nutritional deficiency and part may be due to management. “Some people shoot themselves in the foot; they overfeed and pamper the replacement heifers (as weanlings and yearlings) to make sure they will breed, then after their first calf they don't get any special treatment and lose weight—and don't rebreed.” This is the age group that has the hardest job, and the one group that the ranch might give a little leeway if they didn't breed up as early, especially if they're raising big calves.

“The yearling heifers, by contrast, should have a short breeding season (45 days, the equivalent of two heat cycles). If they don't breed up right away, they ought to be sold,” he says. This is the age to sort and cull, regarding fertility and efficiency. If they are slow to breed at this age, they are not the kind you want to keep.

“Even though you've spent the time and money getting a replacement heifer to that age, she should not be given any slack in this area.” Pregnancy testing these heifers soon after a relatively short breeding season is helpful because you should never keep a yearling that's a slow breeder—and you can then sell the open ones early in the summer when the market for them is best. “One advantage to pulling the bull out after a defined breeding season is that this eliminates the wiggle factor and you aren't tempted to keep a heifer that bred late,” he says.

If you are trying to determine when they were bred, preg-checking is never 100 percent accurate. “There's enough individual variation among cows to make it difficult. A cow can calve up to two weeks early, or late. An example that illustrates this was a study some years ago, published in BEEF magazine, where they were talking about length of calving season. In this study, 100 heifers were synchronized and bred on one day. Even though they were all bred the same day, their calving season was a month long,” he says. Gestation length can vary that much, with some calves arriving two weeks ahead of their due date and some two weeks late.

“Personally I've noticed when ultrasounding cattle, that I'm not as accurate in my palpation (in determining stage of gestation) as I thought. There's enough variation in cows, when palpating rectally, that you can be fooled. Some are farther along than what they feel like (when assessing the size of the uterus, amount of fluid, etc.) and some that are little shorter,” he says. Taking the bull out after a defined breeding season also helps when it comes time to pregnancy test because it eliminates those questionable ones that might be borderline.

Studies have shown that accuracy in checking by palpation decreases in later months of gestation. “Early in pregnancy the veterinarian can determine pregnancy by the size of the uterus. As the cow gets a little farther along you can actually bump the fetus within the uterus. When she get out around 100 to 110 days of gestation, the uterus has dropped down farther below the pelvic rim and you can't reach the entire uterus. At this point you start going by the size of the buttons (cotyledons). As a back up you can assess the diameter of the uterine arteries. When you get past about four months, then you do a lot of the aging mainly by the size of the cotyledons, assessing the size of the arteries as a back-up. There will be some tiny changes, so it is easy to be a couple weeks off in your estimation of the length of pregnancy,” says Hoffman.

He feels the ideal time to preg-check by palpation is somewhere between two to four months of gestation, for best accuracy in determining how far along the cow might be. “Some of this is personal preference. A month of gestation is still fairly easy to determine, but as a rule the two to four months is a better window,” he explains.

Ultrasound is another option for checking. “It's more accurate, especially as far as dating when the cow was bred and when she should calve. If you are going to ultrasound, you can do it even earlier, like in the 30 to 60 day range, and be very accurate. This is a big advantage to some people, especially if the cattle are handy and not out on summer range. You can diagnose pregnancy earlier, and send the open ones to market sooner,” he says. With ultrasound, you can actually see the embryo or fetus. “You can pick up signs of pregnancy at 21 days or even a little earlier” he says.

“The cost of ultrasound is about twice that of rectal palpation, but the improved accuracy is worth it, to many producers. Ultrasound is getting to be the standard method in dairies, not only because of better accuracy, but also because you can diagnose other things (ovarian problems and other reproductive issues). In beef cattle, ultrasound hasn't caught on as much yet, but in some places more producers are using it. I have a friend in Montana who is ultrasounding most of the larger beef herds in his region. They have corrals out on the range pastures and he runs an inverter off his truck to power the ultrasound machine.”

Some ranchers are doing it because of the timing—to detect open cows early for marketing purposes. At the same time you have better accuracy and know you are not selling a pregnant cow that was diagnosed open. “Ultrasound isn't 100 percent accurate, but is more accurate than palpation, especially when checking cows early. By the time a cow is five or six months along the odds of calling her open when palpating are small, compared to checking her at 30 days,” says Hoffman.

The advantages to ultrasound include earlier accurate diagnosis, and the ability to see the sex of the fetus. This is helpful in some purebred operations, especially if they want to sell a group of cows or heifers that will all have bull calves, or all have replacement heifers, for instance.

“In our region I've only done a few beef herds. One producer had me ultrasound a bunch of older cows that had only been bred for a short time. He wanted to make sure they were pregnant before he sold them, and at that stage of their pregnancy ultrasound would be more accurate than palpation,” says Hoffman.

He likes to pregnancy test his own cow herd about 75 days after turning in the bulls. “Anything I have a question on, which is usually less than 10 percent of the herd, I run back through and check with ultrasound. I leave my bulls with the cows for ease of management (rather than take them out at the end of breeding season), but by preg-checking after they should all be settled, I can sell any open or late cows when the timing is best (marketwise). One downside to early preg-checking is that it is possible to have some early abortions, and a cow you thought was pregnant may end up open. And, if you leave the bull with the cows this may mean some of those cows will breed back to be late calvers.”

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