If you want to make sure that you get calves on the ground, pay attention to body score, when you calve, and vaccinations.
That was the message from Cheryl Waldner, a professor in large-animal clinical sciences at the Western College of Veterinary Medicine at the University of Saskatchewan.
“You need to get the cattle cycling at the start of the breeding season and we need to get conception rates to ensure herd fertility,” Waldner said during a recent Beef Cattle Research Council webinar.
Normal open rates in a herd are about six per cent, according to data from the Western Canadian Cow-Calf survey, which covered 64,000 breeding females, she said. But there was a lot of variation — ranging from about two per cent to 12.5 per cent (or more) for individual herds. For heifers (which tend to have higher open rates), the average was 8.5 per cent, but ranged anywhere from zero to 24 per cent in some herds.
So what can you do to beat those average numbers?
“When you breed in May or June, you get slightly lower open rates than herds that start breeding in July or later,” said Waldner.
However, the difference isn’t huge, and she advises caution before moving breeding dates.
“If you start to breed calves in the last weekend in February or March, keep in mind that we are pushing cows a little harder if they are being asked to get pregnant in the summer breeding season,” she said.
Pasture management and nutrition are important considerations during this time.
“It’s not enough just to get cows pregnant,” she said. “We need to make sure that cows carry calves to term and deliver a healthy calf.”
The survey didn’t find abortions to be an issue — the typical herd had less than one per cent of abortions for both calves and heifers. And there was no correlation between late-season breeding and abortions.
“Abortion rates are low and they’re not particularly seasonally dependent. That’s good news,” said Waldner.
Stillbirths are generally about 1.8 per cent for cows, and 2.7 per cent for heifers, with the risk lower for cows bred in June, July and August versus those bred earlier. As well, cows bred in May and June had slightly lower pregnancy rates. Droughts also had an impact on stillbirths, and this was seen particularly in research done in 2001 and 2002.
Improving the odds
Body condition score is a key factor in open rates.
The scoring system used in Western Canada runs from 1 (thin) to 5 (heavy), with most cattle falling in the 2 to 4 range. Those with a 2 (visible short ribs) had open rates 3.5 to 4.3 times higher than those with a 3 (short ribs that can be felt with hand pressure).
“The surprising thing for me was that when we looked at cows that are 3.5 — on the heavier side — they were more likely to be pregnant than cows that were a 3,” said Waldner. “Cows that were 3s were 1.2 times more likely to be open than cows that were 3.5.”
Cows with a score of 2.5 also experienced a dip in pregnancy rates but there wasn’t a huge decline in pregnancy rates with cows that were a 4 or 4.5.
Body condition score is also linked to abortions.
Those with a score of less than 3 were 1.6 times more likely to abort while cows with a body condition score of 2 or less pre-calving were three times more likely to have a stillborn calf. Those with a 2.5 score were 1.5 times more likely to have a stillbirth than 3s. (However, thinner cows — 2s or less — are likely to need a hard pull during their calving.)
Copper levels affected pregnancy rates, especially in two- to three-year-old cows. Of 2,000 cows sampled in 2014, 43 per cent were found to be copper deficient, and 88 per cent of herds had at least one deficient cow.
It also pays to vaccinate.
Vaccinating for bovine viral diarrhea, campylobacter, and infectious bovine rhinotracheitis can also improve pregnancy rates, and prevent abortions, said Waldner.
Cows vaccinated for BVD and IVR also got pregnant a week earlier than cows that weren’t. Those on community pastures and not vaccinated were three times more likely to be open and two times more likely to abort.
Visit the Beef Cattle Research Council’s website on body condition scoring to learn more.