Failed transfer of passive immunity: new guidelines, same message

By ACER Consulting Ltd.

Have you ever been told that colostrum management is the single most important practice in calves? I’m sure you might have and there is more and more research being completed that is showcasing just how true this is. A recent study highlights that we may need to reconsider our thresholds for what we define as failed transfer of passive immunity, which is an inability to reach appropriate levels of Immunoglobulin G (IgG) in the bloodstream of calves.

Why do we need to change the guidelines and what are they?

Traditionally, we have used a cut point of IgG in the blood of 10 g/L to define failed transfer of passive immunity. However, many recent studies have highlighted that to optimize protection against disease we need to achieve higher thresholds.

It was determined that we need to recategorize and target higher thresholds of IgG in the blood for passive transfer to prevent calf morbidity and mortality. This is highlighted below in the two figures where calves with excellent passive transfer (> 25 g/L of IgG) had significantly reduced levels of disease and mortality compared to the other groups. In addition, the two middle groups with good (18 to 24.9 g/L) and fair (10 to 17.9 g/L) passive transfer also had reduced levels of disease compared to the traditional < 10 g/L levels.  

What are the targets?

Based on the research that has been done, it has been suggested to categorize passive transfer into four categories: (1) Excellent, (2) Good, (3) Fair, and (4) Poor, based on levels of IgG and/or total protein in the blood, as outlined in the table below. The table also provides suggested targets on the percentage of calves that we should aim to have in each category. The final two columns of this table highlight the results from recent studies on how farms in Ontario and the United States have done in attaining these benchmarks.

In the Ontario study, 112 dairy farms were visited with blood samples collected from 846 calves, whereas the study completed in the United States visited 103 dairy operations with samples collected from 2360 calves. Both studies highlight that there are areas to improve with respect to colostrum management. It should be noted, however, that significant improvements in passive transfer have been made with previously more than 37 per cent of calves sampled on 113 dairy farms across Ontario being in the poor category. 

Category	Serum (IgG g/L)	Total Protein (g/dL)	% Brix	Target (% calves)	Current Ontario level (% calves)	Current USA level (% calves)
Excellent	> 25.0	> 6.2	> 9.4	> 40	32%	36%
Good	18.0 to 24.9	5.8 to 6.1	8.9 to 9.3	~ 30	17%	26%
Fair	10.0 to 17.9	5.1 to 5.7	8.1 to 8.8	~ 20	32%	27%
Poor	< 10.0	< 5.1	< 8.1	< 10	19%	12%

When and how frequently should we take samples?

Ideally, blood samples should be collected from calves that are between one to nine days of age to determine passive transfer status. The answer to determine how frequently samples need to be taken depends on your farm. Ideally, if you haven’t sampled calves in the past, it is important to establish an accurate baseline where samples from 12 calves or more are collected.

After establishing a baseline, if an opportunity for improvement is identified, it is worth monitoring the impact that changes made to colostrum management have. So, sampling another 12 calves after the management change can give you important insights. If after the baseline sampling your farm is meeting your targets, continue to monitor on a monthly or bi-monthly basis to ensure the levels of passive transfer are not changing.  

Take home messages

The thresholds for passive transfer have changed based on new research highlighting that higher targets for IgG are needed for optimal calf health and welfare. Having passive transfer data can really help in making informed management decisions. When not meeting the thresholds, focus on colostrum management including quantity of colostrum, quality of colostrum, cleanliness of colostrum, and quickness of colostrum feeding. Work with your veterinarian to develop a monitoring plan for transfer of passive immunity on your farm.

This project was funded by the Canadian Agriculture Partnership, a five-year federal-provincial-territorial initiative.