Any dairy producer will tell you that when it's comes to getting a dairy cow pregnant, sooner is better than later. The sooner she's bred, the sooner she'll calve and the less time she'll spend out of the milk production cycle.
But ironically, when it comes to confirming that the cow is pregnant, later may be better than sooner, according to research by Paul Fricke, University of Wisconsin-Madison extension dairy specialist.
It's hard to be patient, Fricke acknowledges. After all, the whole idea behind today's timed artificial insemination approach, in which farmers use treatments to synchronize cows' ovulations, is to get breeding on a reliable schedule. If a cow doesn't get pregnant on schedule, farmers want to know as soon as possible so they can repeat the synchronization and insemination protocol.
The problem, says Fricke, is that positive results from pregnancy tests done early in gestation can be deceptive. One reason is that some tests can yield false positives early in gestation. But even more important, early gestation is when there's the greatest chance of a cow suffering a pregnancy loss.
So the earlier you check, the greater the chance that the cow that tested as pregnant won't stay that way. And because of that early positive diagnosis, it may take you longer to discover the pregnancy loss and get the cow back into the breeding lineup, which means a longer interval out of the milk line.
Fricke cites one study showing that eleven percent of cows suffer pregnancy losses between 28 and 42 days after insemination. That drops to 6 percent between 42 and 56 days and to 2 percent at 56 to 98 days.
"Your diagnosis of a cow being pregnant at 19 days is confounded by early pregnancy loss," Fricke says. "That diminishes the benefit of early pregnancy detection. The magnitude of the pregnancy loss is greater the earlier post breeding you make a positive diagnosis."
And Fricke's studies suggest that there's little incentive to check that early anyway. He's found that fertility is better when a resyschronization of ovulation is started 33 days following insemination than if it's done at 19 to 26 days.
"When you add this up, you get the counterintuitive notion that you can improve reproductive efficiency by waiting to preg check 32 to 39 days after insemination rather than checking at 26 or 27 days," Fricke says.
"Based on what we see, the need for a non-pregnancy diagnosis before 32 to 39 days following timed artificial insemination is questionable," Fricke says.
Research is underway on several strategies for improving pregnancy diagnosis methods.
Studies are showing that B-Mode ultrasonography is less invasive than transrectal palpation by hand and gathers a great deal more information. Imagery can provide information about ovarian health, twins, and fetal sex.
Work is also being done on pregnancy-associated glycoproteins, which can be detected in the cows' bloodstream as early as 30 days after insemination.
Research is also being done on new strategies to resynchronize cows that fail to conceive after a previous insemination. The results should help shorten the interval between timed inseminations and improve conception rates.
In the meantime, says Fricke, while the new approaches are being tested, the best advice for dairy producers is to wait a bit on pregnancy checks. And for those who can't wait, Fricke suggests that a cow animal diagnosed as pregnant early in gestation be scheduled for retesting later on.