This article originally appeared in the Wisconsin Agriculturist

The importance of colostrum is no secret to dairy and livestock producers. Unlike many other species, the placenta of cattle prevents the transfer of antibodies from the dam to the calf in the uterus. Instead, calves must rely on colostrum, the cow’s first milk, to pass antibodies from dam to calf. Failure to receive and absorb immunoglobulins from colostrum results in what’s called Failure of Passive Transfer (FPT) of immunity. There are direct links between FPT and increased calfhood illness and mortality. It is a farm management and staff’s responsibility as stewards responsible for animal welfare to ensure all calves, regardless of if they are a dairy replacement heifer, bull, or beef x dairy crossbred calf, receive sufficient quantities and quality of colostrum on time.  

A newborn calf’s small intestine can absorb the immunoglobulins contained in colostrum for only a limited time. Absorption rates begin to decline just four hours following birth. By 24 hours after birth, the intestinal wall closes preventing the absorption of immunoglobulins from colostrum. That leads us to goal number one: calves should receive their first colostrum feeding within 4 hours of birth. A second colostrum feeding within 12 hours of birth is also advisable. 

What about amount? The general recommendation is to feed 10 to 15% of the calf’s birth weight. If we use back-of-the-envelope math one gallon of milk weighs 8.6 pounds. For an 80-pound calf that means approximately one gallon of colostrum is recommended. One gallon also equates to 4 quarts, which we commonly see as the recommended feeding amount. That said, know your calf weights. For smaller breeds, adjust down. For larger calves, we should be adjusting upward. 

Quality colostrum 

Colostrum quality is another factor. Visual assessment can tell us a little, but not everything. Colostrum should be thick in consistency and yellow in color. Watery, bloody, and manure-contaminated colostrum should be discarded. To truly know quality, it needs to be tested. Testing can be done with a Colostrometer or Brix Refractometer. Each tool has its pluses and minuses, as well as specific instructions for use. The take home, for now, is we want to feed high-quality colostrum, defined as greater than 50 g/L immunoglobulins measured with a Colostrometer, or 22% Brix or higher if measured with a refractometer. We have options to work around poorer quality colostrum. We can still feed it but with the addition of a colostrum supplement product. We can not feed it, and instead feed a colostrum replacement product or colostrum from another cow known to be high quality. 

Now for upping our game. Recent research (Lombard et. al., 2020) revealed that what we previously thought was satisfactory for Transfer of Passive Immunity (TPI) in calves was insufficient. The success, or failure, of TPI in calves can be tested by measuring serum IgG levels. This is a test that can be done on farm by collecting jugular blood samples from calves and testing the blood serum. Serum IgG tests give us valuable information on the effectiveness of our colostrum feeding protocols. Calves testing low for serum IgG are most likely either not receiving enough immunoglobulins from colostrum (quality and/or quantity issue) or not absorbing them (timing issue). Historically, serum IgG levels ≥10 were considered passing and <10 was considered failing.

The new standard utilizes four categories

• Excellent at ≥25 IgG
• Good at 18.0-24.9 IgG
• Fair at 10.0-17.9 IgG
• Poor at <10 IgG

What would have slipped by as just above passing a few years ago will now score you a letter grade “D.” Recent survey work by Extension Educators in Wisconsin found all of farms in the survey fed colostrum on time, but the amount and quality may have been too low in some cases. 

There is good news

We already know how to meet the new standards for TPI. It is by being vigilant in monitoring colostrum quality, quantity, and time of feeding for our newborn calves.  

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