New Passive Transfer of Immunity Standards Established
Over the past two years, I have had the privilege of working on a special project with many of the most respected minds in the country who focus on raising dairy calves.
Our purpose: to revisit the industry standard on how we measure the success or failure of passive transfer of immunity in calves. In recent years, there has been growing concern that the long-standing “pass or fail” standard of 10 g/L of serum IgG in young calves was: (a) too low, given our knowledge that much higher levels could be achieved; and (b) too limited in scope to truly motivate improvement in colostrum quality and delivery on U.S. dairy farms.
The NAHMS studies committee led by Dr. Lombard to reevaluate the success or failure of passive transfer of immunity in calves.
We know from a number of research studies that higher levels of serum IgG and serum total proteins (TP) are almost linearly predictive of calf health and survivability. The higher the number, the better the calves do. We also had evidence that colostrum management has improved considerably over the past several decades.
“We wanted to raise the bar in terms of on-farm colostrum management, because we believed in the merits of doing so.”
In the “National Dairy Heifer Evaluation Project” study conducted in 1991-92 by the National Animal Health Monitoring System (NAHMS), 41% of calves were shown to have failure of passive transfer of immunity because they did not meet the 10 g/L threshold for serum IgG. By 2014, just 13.7% of calves fell into that category in an updated NAHMS study.
Our committee was led by USDA veterinarian Dr. Jason Lombard, who also manages the NAHMS studies. As we dug into the issue, one of our initial discoveries was that the 10 g/L standard was established in the 1980s. It was based on very limited research, and factored only death loss, instead of also examining illness incidence. We knew we could do better, and set out to modernize the standards to more effectively reflect current industry practices and capabilities.
After thoughtful examination of data and careful deliberation, we arrived at a four-level evaluation system that classified serum IgG levels as Excellent, Good, Fair and Poor, and assigned herd-level target percentages to each category. We also converted IgG levels to common on-farm methods of evaluating immunity that serve as a proxy for measuring IgG: TP, and Brix percentages.
Following are the new standards recommended by the committee, which will be published in an article in the Journal of Dairy Science:
Table 1. Consensus recommendations on levels of passive immunity in dairy calves in the United States.
In Press: Journal of Dairy Science
One of our key priorities throughout the project was to ensure that the new standards were both realistic and achievable. We wanted to raise the bar in terms of on-farm colostrum management, because we believed in the merits of doing so. But we didn’t want to make the standards so high that they created the opposite intent by discouraging producers.
After consensus on the new standards was reached, Dr. Lombard and his colleagues performed an interesting exercise. They evaluated recent NAHMS data for more than 2,500 heifers nationwide, sorting their IgG levels according to our new herd-level target percentages for calves in each category. The outcome: Excellent – 35.5%; Good – 25.7%; Fair – 26.8%; and Poor – 12.0%. These results gave us confidence that the standards we proposed were well within the realm of realistic achievement on U.S. dairy farms, while still providing guidelines for improvement.
It was humbling and energizing to work collaboratively with so many knowledgeable individuals on this project. We come from many backgrounds – private and public researchers, university educators, management consultants, industry representatives, and practicing veterinarians. What we share is a common passion for healthy dairy calves and serving the U.S. dairy producers who raise them. I believe these new standards will serve our industry well for many years to come.
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