When is the best time to test calves for passive transfer of immunity? The answer: It depends.

Quantify immune protection in calvesMost studies suggest that you should wait until the calf is at least 24 hours old for blood sampling in order to capture peak blood serum total protein (BSTP) values, explains Sam Leadley, calf and heifer management specialist with Attica (N.Y.) Veterinary Associates. However, a few studies show less than 10 percent variation among BSTP values from blood samples taken at 24, 48 and 72 hours of age. Study results start to get more variable beyond three days of age.

So should you be concerned about when the blood samples are taken?

“If, on one hand, 90 percent of your values are already at 5.5 or above, don’t sweat the small stuff – continue your current sampling practices,” Leadley says. “If, on the other hand, 20 percent or more of your values are below 5.0, you may want to make an effort to collect the next 12 or 15 samples in the one- to three-day range just to be more certain you have valid values.”

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