Producers often want more information than whether a cow is pregnant, but it’s important for the diagnosis to be correct
Open cows are expensive to keep, and never more than during a year of feed shortages.
It adds importance to pregnancy checking, along with the fact that an abundance of open cows can indicate disease in the herd that should be addressed.
Pregnancy testing methods include palpation, ultrasound and blood tests. Rectal palpation is the traditional method still used by many veterinarians. Clues that a cow is pregnant can be detected as early as 30 days and definitely by 45 days of gestation. Changes can be felt in the uterus, ovaries and uterine arteries through the rectal wall.
Experienced veterinarians can estimate stage of pregnancy with fair accuracy but it’s more difficult in late gestation because there’s more variability in size of the cotyledons and fetus.
Many veterinarians now use ultrasound, which can reveal sex of the calf if checked in early pregnancy and can assess viability of the fetus.
Trans-rectal ultrasound can show the embryo or fetus as early as 26 days. A traditional arm-in rectal probe can be used but the newer extension-arm probe eliminates the need to put an arm into the cow.
Dr. Don Driedger of Driedger Veterinary Services in Lloydminster, Alta., does a lot of pregnancy testing in commercial herds and some purebred herds.
Purebred breeders often want more information than whether a cow is pregnant, including sex of the fetus and how long it has been bred, to determine if it conceived from artificial insemination or from a cleanup bull.
In general, any cattle producer benefits from knowing which cows are open.
“It enables producers to have an inventory of how many cows they will be feeding, going into winter, and know how much hay they will need,” says Driedger.
“My clients, on average, have about 200 cows. At $5 per head for the preg checking, that’s $1,000. If we find seven to 10 percent open, and those cows can be sold, in just one month of feeding hay this saves about 30 big bales of hay at $60 per bale, or about $1,800.”
Accuracy is important.
“If a veterinarian makes a mistake and the producer sells a pregnant cow (thought to be open), this is costly for the producer. Ultrasound can be more accurate than palpating and a person is less apt to make that mistake,” Driedger says.
“But I use ultrasound mainly for my own benefit. It has enabled me to continue preg-checking because I don’t wear out so quickly. Extension-arm ultrasound is also quicker because I don’t have to ‘visualize’ with my hand. I see it with my eyes.”
Many veterinarians use ultrasound. The first method was arm-in trans-rectal but now many use extension-arm models.
Dr. Andrew Bronson came to Alberta after graduating from veterinary school in 1982 and went into beef practice. By age 45, multiple strain injuries took a toll on his arm and shoulder after palpating cows all day.
He bought an aluminum extension-arm ultrasound unit and then he and a partner developed their own version called ReproScan.
Use of ultrasound equipment is easier to learn than palpation, he says, and at certain stages of gestation, it more accurately determines age of the fetus.
“Then as the cow gets farther along in the pregnancy, ultrasound is not as accurate as palpation for someone who’s done a lot of palpations. But the ultrasound is probably more accurate for the inexperienced person because it’s easier,” says Bronson.
Ultrasound does a good job of aging a fetus at 30 to 120 days. Both palpation and ultrasound become less accurate in advanced pregnancy. There are also variations in fetal size influenced by genetics and nutrition.
“If you put the extension arm in there, however, and see large cotyledons and maybe a hoof, you can say it’s at least six months along. When palpating, if you are good at this, you can get a feel for the weight of the uterus, size of uterine arteries, etc. and all these things can provide helpful information,” Bronson says.
“Palpation is a difficult skill to learn. It’s hard for young veterinarians to gain experience quickly enough to become good. It’s easier to learn ultrasound. Extension-arm ultrasound makes it even easier and there are now portable units.”
Bronson is retired but still trains people to use ultrasound. Most are veterinarians, but producers with large cow herds also want to learn.
“There’s a lot of value in being able to get cows checked when and where they want to do it. It’s often better to check sooner than later, but many producers are trying to extend their grazing seasons and some are mixed farmers and don’t want to bring their cows home from pasture just to pregnancy test them.”
Bronson talked last fall with those at a large British Columbia ranch that has more than 1,000 cows.
“They have corrals in various locations out on the mountains where their cattle graze. They might be able to preg check at weaning time and just leave the cows out there to graze but pick out the culls to sell before they lose weight.”
Clients must know that when cows are checked in early pregnancy, a few will lose those pregnancies. A cow deemed pregnant at 30 to 45 days may not be pregnant later. Then the client may think the vet made a mistake.
Driedger usually checks cows in commercial herds when they come home from pasture. The fetus is bigger by then and may have dropped beyond the cow’s pelvic rim.
“It’s hard to go in deep enough with ultrasound, so in these instances I may also check with my hand to know if there’s a calf down there. These cows will be some of the first-calving cows in the herd.
“I think it’s good to have a veterinarian who has the ability to use both palpation and ultrasound,” he says, because there is less chance of error.
Bronson says there isn’t much profit margin on ranches, especially in a dry year.
“A three-cycle breeding season is plenty long enough. When the cows are preg-checked, you need a certain cut-off date. Anything that is not 90 days pregnant should be culled because those calves will be born late.”
Any cow that is old or potentially on the cull list should be fetal-aged to know if she should be kept or sold.
Some veterinarians encourage clients to learn how to ultrasound because there’s a shortage of veterinarians in rural large-animal practices.
“They teach some of their clients how to do it and recheck the open ones for them until they get really good at it,” says Bronson.
Some ranchers do blood tests for a yes or no pregnancy diagnosis, which is an option for those with only a few cows or who live far from a veterinary service.