A calf is born with little or no antibodies. It gets them from two sources - the calf generates them itself (this can take weeks and leaves the calf exposed to infection) or it gets them "passively" by absorbing antibodies in its mother's colostrum.

Late in her pregnancy, the cow selectively concentrates antibodies into colostrum. This is a one-time event. If the colostrum is lost, it's not remade. The antibodies present are determined by her disease and vaccination history.

The ability of the calf to absorb IgG molecules (immunoglobulin type G molecules - the most important antibody) across the gut is a one-time event for the newborn calf. The gut closes in about 24 hours.

If the calf doesn't get colostrum and absorption doesn't occur, closure will be delayed a bit, but it will still occur, severely curtailing the calf's ability to absorb adequate IgG into the blood. The sooner the calf gets colostrum, the higher the passive transfer.

The Role Of Passive Transfer Passive transfer of colostral immunoglobulin to the calf is critical for calf health. Studies show that calves with inadequate serum IgG concentrations at 24 hours of age are 3.2 to 9.5 times more likely to become sick and 5.4 times more likely to die before weaning.

But, the impact on production and profitability goes beyond the obvious costs of sickness and death. Studies also show that sickness during the first 28 days of life can cut expected weaning weight by 35 lbs.

There's a high awareness among producers of the importance of colostrum. Even so, a great number of herds have inadequate passive transfer ofIgG. One research project reported that 11% of 70 beef calves did not have adequate levels of passive transfer.

Another project found 21% of 48 calves of first-calf heifers and 23% of 263 mature cows had levels of IgG too low to ensure adequate disease protection. In an unpublished study in two separate years, a 208-head sample of 1,000 calves from a well-managed, commercial cow-calf ranch found 30% of the calves with low IgG levels. It's clear a large percentage of calves are not achieving adequate passive transfer.

Factors Affecting Passive Transfer There's a long list of factors affecting the success of passive transfer. The two most important are age of calf at consumption and mass of IgG consumed.

The goal is to ensure the calf consumes 200-400 grams of IgG. This can be done using a variety of thumb rules. These include:

* Feeding 10% of the calf's body weight (3.2 qt. in a 70-lb. calf);

* 25 cc/lb. calf body weight (1.75 qt. in a 70-lb. calf);

* Or feeding 2 qt. within the first 12 hours of life.

The level of IgG concentration and the volume of colostrum vary greatly between females. Reports of average IgG concentration range from 75 to 150 grams/qt. and colostrum volumes range from 2.4 to 3.1 qt. Some cows easily provide enough IgG in just a single quart. Others can't deliver enough IgG in their total volume of colostrum.

One option for high-risk calves less than 24 hours old is to administer them supplemental colostrum. The first choice would be colostrum from the calf's dam. The second choice would be colostrum from a herdmate of the dam. The least preferable would be colostrum from outside the herd, such as dairy colostrum.

Controlled, independent studies on colostrum substitutes have been few and limited in size. Perhaps as a result, the effectiveness of substitutes hasn't thus far been shown. Based on available information, it's difficult for us to justify the cost of colostrum substitutes.

After gut closure occurs at about 24 hours, therapeutic options are limited. In a study of a few colostrum-deprived dairy calves, treatment with intravenous or intraperitoneal plasma failed to provide serum IgG concentrations or clinical protection equivalent to colostrum feeding. This is another area that needs more research before we can recommend it as anything but a desperate intervention.

Don't Forget Environment This discussion wouldn't be complete without mention of environmental effects on passive protection. Minimizing disease challenge is critical to preventing disease.

Herds with good colostrum management can still have excess levels of calf sickness if they calve in filthy conditions. By optimizing the calving environment it's possible to remove the negative impact of high rates of failed passive transfer, such as in groups of first-calf heifers. This can be a critical control point for herd managers.

Calves that don't get enough colostrum are at risk of poorer health and growth performance. Strategies to reduce this risk include: culling dams with mastitis, improving udder conformation, reducing the number of young or thin cows, and minimizing the number of cows that experience dystocia or have weak calves and twins.

In addition, producers must monitor cattle to ensure that the calves suckle and to provide appropriate attention; i.e., make sure calves receive approximately 2 qt. of colostrum within the first 12 hours of life.