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Veterinarian View | May/June 2024

What is Failure of Passive Transfer?

contributed article by Dr. Vince Collison, Collison Embryo and Veterinary Services,

Rockwell City, Iowa

When we talk about passive transfer in calves there are two parts. The first part is the transfer of antibodies from the mother’s colostrum across the calf’s inner gut surface into its blood system. The primary antibodies in colostrum are the IgG variety that circulate in the blood to cause protection from various infections.

The second part is that it is a passive immunity. By this, we mean that since the antibodies come from the mother’s colostrum and are not actively made by the calf’s own immune system, it is a passive form of immunity. So, a calf is essentially born without any immunity and depends on this passive transfer of antibodies to protect itself from exposure to infection early in life.

In order to acquire levels of antibodies that are protective, it is essential that the colostrum has high levels of antibodies and is consumed quickly after birth in large amounts. So, not only is there a quality component to colostrum, but also a quantity component that is probably even more important.

Failure of Passive Transfer

When we talk about the failure of passive transfer (FPT) in calves, these are calves that are older than 24 hours with levels of antibodies in their system that are not high enough to be protective. After 24 hours of age, they can no longer acquire antibodies into the blood system through the milk. To reach protective levels in the calf’s system, they probably need to ingest at least 200 grams of IgG through the colostrum.

What Situations Cause Failure of Passive Transfer?

Listed are some of the common causes:

1) Poor milking cows. This can be a cow that is getting too old or just doesn’t milk well enough to provide the volume of colostrum needed to reach levels of immunity.

2) Bad udders. Often these cows have teats that are enlarged and ballooned out. When the teat becomes that enlarged, it is hard for the calf to make a connection without intervention.

3) Poor mothers. Cows that are too nervous to mother their calf or they just don’t care about the calf. In these situations, you can have calves with failure of passive transfer unless there is some intervention.

4) Cold weather. If calves get chilled out, the cold stress can make it hard for them to absorb colostrum effectively. Warming a calf up prior to giving colostrum would be a benefit.

5) Delayed assistance. Waiting too long to give supplemental colostrum or assist a calf with nursing. The ideal time to get the most antibody absorption from colostrum is in the first two hours. The gut will start shutting down over the next 24 hours, so colostrum ingested at 12 hours is probably not going to be as effective as when it’s given at two hours after birth.

6) Poor colostrum quality in the dam. This can be caused by various factors. A cow that is getting too old. Buying new bred heifers that have not had time to acclimate to their new herd. Not getting the cows vaccinated pre-calving against specific disease issues for the herd. Not meeting the nutritional needs of the dam pre-calving. Extended severe weather stress prior to calving.

7) Separation. Separating calves from their dams in the first 24 hours. If you use calving pens to get cow/calf pairs bonded in the first 24 hours, they need to stay together. If you turn the cow out to drink or eat for any period of time, you are restricting the time the calf can nurse the cow. It’s pretty easy to turn a cow out with the intentions for them to eat or drink for an hour, but that can easily turn into three to four hours if you get busy with other things.

Testing for FPT

If we suspect a failure of passive transfer, the calf’s blood serum can be checked with a BRIX refractometer. The BRIX refractometer measures the dissolved solids in a solution. It gives a reading as a percentage by mass of the solution. It is used to measure the amount of sugar in the solution in the brewing industry and can be used to estimate the amount of IgG in serum. There is a refractometer that can measure total serum protein, but the BRIX refractometer is cheaper and can also be used effectively.

Levels of IgG at less than 10 grams/liter in serum can be considered a failure of passive transfer. If levels of IgG are in the 10 to 24 grams/liter range, adequate passive transfer has occurred. If levels of IgG are at 25 grams/liter or higher, then excellent passive transfer has occurred.

To correlate this to a BRIX refractometer percentage, a reading of 8 percent on a BRIX is about the equivalent of 10.1 grams/liter of IgG and would indicate a successful passive transfer. Levels of 8 to 9.4 percent on the BRIX would correlate to the adequate range of passive transfer at 10 to 24 grams/liter of IgG. Any reading on the BRIX at 9.5 percent or higher would correspond to excellent passive transfer at 25 grams/liter or higher of IgG. If you are getting a reading of less that 8 percent on the BRIX refractometer, the levels of IgG are probably less than 10 grams/liter and would indicate a failure of passive transfer.

Passive Transfer

While the calf can and will develop their own active immunity, that takes time and their immune system is not equipped to handle challenges from various infections without adequate passive transfer. While you can vaccinate new calves for various things, it can never replace the effectiveness of passive transfer of antibodies through the colostrum.

This is why management of passive transfer is so important for calf health and getting off to a good start. The passive transfer is what keeps the calf healthy until they develop their own active immunity.

The goal should be to get a calf that is up and nursing within the first 15 to 30 minutes of being born. If this occurs and everything is right with the cow’s nutrition status, the calf should be on its way to achieving a normal passive transfer of antibodies. If there are any issues that are preventing this from occurring, it would be better to error on the side of intervention earlier than later, as passive transfer is a race against time to achieve adequate levels of IgG in the system.

Dr. Vince Collison is co-owner of Collison Embryo and Veterinary Services PAC

in Rockwell City, Iowa.

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