November 4, 2010
Knowing which cows are open gives a rancher alternatives: you can wean calves early to sell open cows at peak market prices, sort off thin cows to fatten
before selling, or sell open heifers when they will still bring top dollar.
Of course, another reason to preg check is to monitor the herd’s health and reproductive status. Finding more open cows than usual can signal a disease problem such as infectious bovine rhinotracheitis, bovine viral diarrhea (BVD) or sexually transmitted diseases that cause cows to abort.
Nutritional deficiencies in a herd can also show up as open cows, especially in two-year-olds that should have bred back for their second calves. Some producers also use pregnancy testing to determine when cows will calve, facilitating sorting them into early- and late-calving groups.
According to 2007-08 National Animal Health Monitoring System data, about 20% of beef cow-calf producers use pregnancy testing or palpation in their herds. However, the benefits of this practice are fairly simple to realize, says Les Anderson, University of Kentucky Extension beef specialist. Compare the roughly $5/head cost of a pregnancy exam with the $100-200/head cost of hay alone to feed an open cow through the winter, and pregnancy testing quickly pays for itself, he says.
Producers have several options for testing, including palpation, ultrasound and a blood test. Each method has advantages and disadvantages and what you choose may depend upon your individual operation.
Palpation – Rectal palpation is the traditional method. Indications of pregnancy can be detected as early as 35 days – and definitely by 45 days – by feeling the uterus, ovaries and uterine arteries through the rectal wall. The position of ovaries changes as pregnancy advances; the increasing weight of the uterus pulls them deeper into the abdominal cavity. After the fifth month, the weight and size of the fetus and its fluids cause the uterus to sink down and rest on the abdominal floor.
Experienced veterinarians can estimate stage of pregnancy (and approximate calving date) with fair accuracy between 30 and 100 days and after seven months. The mid-stage of pregnancy is a little harder to date, after the uterus drops out of reach.
Taking the bull out after a defined breeding season helps when it comes time to pregnancy test because it eliminates those questionable ones that may have just been bred but can’t be definitively determined by palpation.
Disadvantages to palpation include the fact that rough handling of the uterus in early pregnancy can lead to abortion. There’s also risk of injury to the cow, or spreading diseases such as BVD from one cow to another unless a new, clean palpation sleeve is used for each cow. Most practitioners don’t take time to change sleeves.
Ultrasound – Ultrasound can detect pregnancy earlier than palpation, sometimes as early as 13 days after breeding (but more commonly after 21 days), but is more expensive and requires equipment and electricity. It can provide more information than palpation, such as viability of the fetus, incidence of twins, and sex (between 55 and 90 days’ gestation).
Most ultrasound technologies still go into the cow’s rectum with a probe, but less manipulation of the uterus is needed to confirm an early pregnancy. There’s also less stress to the cow/fetus, and less wear and tear on the practitioner’s arm and wrist.
Jeff Hoffman, DVM, Salmon, ID, says the cost of ultrasound is about twice that of rectal palpation, but the improved accuracy is worth it to many producers. Ultrasound is used extensively in dairies, because diagnosis of reproductive issues is more accurate.
While ultrasound isn’t used as much in beef cattle, Hoffman says a Montana colleague is ultrasounding most of the larger beef herds in his region. The ranchers have corrals out on the range and he runs an inverter off his truck to power the ultrasound machine.
“One of my commercial producers had me ultrasound a bunch of older cows that had only been bred a short time. He wanted to see if they were pregnant before he culled them (keeping pregnant ones another year); at that stage of their pregnancy, ultrasound was more accurate than palpation,” Hoffman says.
One downside to checking early (with any method) is that some cows may abort or resorb a pregnancy before calving time. A cow that checked pregnant early on may end up open or very late instead.
Blood test – Several tests using progesterone measurements in blood and milk have been developed to confirm pregnancy. The most useful test to date is a blood test developed by University of Idaho DVM Garth Sasser. He discovered a protein produced by the placenta of ruminant animals that is detectable in blood, and founded a company called BioTracking. His blood test called BioPRYN (Pregnant Ruminant Yes/No) for cattle and other ruminants became commercially available in 2002. There are now 24 labs worldwide handling blood samples.
According to marketing manager Jeremy Howard, the advantages of the blood test over palpation include being able to detect pregnancy sooner. Plus, the blood test is cheaper than ultrasound, more accurate than rectal palpation, and can be done more quickly and easily. Samples are taken from a vein under the tail, which he says is less invasive and traumatic for the animal than palpation. Plus, there’s no risk for spreading disease from one cow to the next, as can happen with rectal palpation.
Blood sampling is also faster than other methods, and ranchers can take samples themselves. Samples are labeled with the cows’ numbers and shipped to a lab, with results sent back by phone, fax or e-mail.
“For the blood test, all you need is a syringe and needle; cost is $2.40/sample,” Howard says. “We can also do our BVD test from those samples for an additional $3.65, if a rancher wants both tests done at the same time.”
More beef producers are testing heifers 30 days after pulling the bull or after synchronizing and artificial insemination (AI). Any open heifers can then be sold before they’re too old to get top beef prices.
The blood test is a great tool if you wait two weeks after AI breeding before putting a cleanup bull with cows. The test reveals which females conceived to AI and which were bred later to the cleanup bull. Breeders using embryo transfer can check recipient cows quickly to determine which are pregnant, and have another chance to use the ones that didn’t take.
Feedlot heifers can be checked upon arrival to see if they’re pregnant. The test is also useful in sale barns, to market cows more efficiently. For instance, after using the blood tests, one auction owner found that 34-40% of cows being called open by a veterinarian doing palpation were actually pregnant – especially the ones that had been bred during the two months prior to checking them. Knowing they are pregnant, he can sell them as bred cows rather than open culls.
Disadvantages of the blood test include having to wait for results (which may take 2-3 days) compared to knowing immediately, and an inability to accurately determine the stage of pregnancy. Ranchers who just work cows one time and split off the open ones to sell won’t find it useful, but operators who have access to the cows more than once – as when giving calves preweaning vaccinations – can process the cows after they know which ones are open.
Heather Smith Thomas is a Salmon, ID-based rancher and freelance writer.
Getting the feel
Here are the stages of pregnancy as detected by palpation.
70 days – The enlarging uterus is readily felt. The amnion sac feels like a solid oval ball (about 2¼ in. in diameter) floating within it.
90 days – The uterus is usually still resting up near the pelvic brim, with the pregnant horn about 3½ in. wide and the nonpregnant horn about 2 in. wide. The fetus can sometimes be felt in the pregnant horn.
110 days (3½ months) – The enlarging uterus has dropped below the pelvic brim (the cervix lies at the brim) and there is fluid distention in the lower part of the uterus.
4-5½ months – It is possible to feel the fetus in about half the cases.
5½-7½ months – It’s more difficult to reach the uterus, but if so, you may be able to touch the fetus’ head or flexed limbs that lie just beyond the pelvic brim.
7½ months to birth – It’s often easier to feel the fetus because it’s grown so much that the front legs are closer to the pelvis. If you can’t reach the uterus, you may be able to feel large cotyledons or a strong vibrating pulse in the enlarged uterine arteries.
Seeing a cow in heat is usually a clue she’s open, but it’s not a dependable way to determine pregnancy. Some open cows don’t cycle if they’re lactating or have a cystic ovary, and some pregnant cows will continue to show heat.
Old-timers used a few other ways to determine pregnancy. Some say you can feel the fetus by about the fifth or sixth month by putting your hand against the cow’s lower flank and making a quick upward and inward push. If she’s pregnant, the fetus should bounce back against your hand.
Another method sometimes used was to milk a little from the cow just after the calf is weaned and put a drop of milk into a glass of water. Proponents of this method claim that if the drop goes all the way to the bottom without spreading out, the cow is pregnant; if the milk droplet spreads out, she’s open.
One other thing noticed by many stockmen is that after you work the herd in the fall and wean the calves, many of the open cows that weren’t cycling during lactation will come into heat shortly after you pull their calves off.
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