“We generally discover problems at pregnancy diagnosis, and try to resolve it for the following year,” says Ahmed Tibary, DVM and Washington State University professor of theriogenology. The overall pregnancy rate might be adequate, but if cows are calving late, something must have happened during the first cycle, he says. 

When there’s a poor pregnancy rate or spread-out calving season, cows should be closely monitored the next breeding season to confirm that breeding activity is occurring or if females are returning to estrus after being bred.

“In one herd, we checked cows halfway through the breeding season to see how many bred in the first cycle. After a 21-day breeding period, we determined pregnancy rate 30 days later by either ultrasound or a blood test to check for pregnancy-specific protein B (PSPB),” Tibary says.

“The blood test works well on heifers, but cows must be more than 90 days post-calving when tested. If they’re bred and tested too soon after calving, there may be some PSPB still in their bloodstream from the previous pregnancy,” he says.

To determine the cause, Tibary looks at the cows, all herd records and historical data to illuminate changes in nutrition or other factors.

“The challenge in investigating poor calving rates is that we’re usually looking back and trying to figure out what might have happened months ago. Were the cows not cycling soon enough (nutritional problem), or did they get bred and lose the pregnancy? If that’s the case, we want to figure out if it was infectious, or due to heat/humidity or some other stress,” he says.

Without information on the cows’ body condition at that time, or nutritional level or mineral status, it’s hard to determine what happened, he says. You could compare pregnancy status to previous breeding/calving seasons, which also necessitates good records.

“You can also look at groups of cows – whether you have the same pregnancy rate/loss in heifers, first-calf cows, or older cows that have had two or more calves,” Tibary says.

Heather Smith Thomas is a rancher and freelance writer based in Salmon, ID.