A typical newborn calf requires at least 100 grams of immunoglobulin to achieve passive transfer of immunity. It’s easy to commit that number to memory. It’s another matter to actually make that number a reality for your calves.
The 100-gram goal is based on several factors explained in the four steps below. Use these steps as a refresher course or to show new employees the value of good colostrum management.
Determine the calf’s blood plasma volume.
In order to determine how much immunoglobulin G (IgG) a calf needs to absorb for passive transfer to occur, you first must determine the calf’s plasma volume, explains Lance Fox, technical service manager with Alpharma, Inc. When you use this rule-of-thumb: Plasma volume is equal to 9 percent of a calf’s bodyweight, it becomes a simple calculation. The following example uses a 41-kilogram calf (90 pounds):
41-kg calf x 9 % bodyweight = 3.7 liters of plasma volume
Calculate the calf’s Igg needs.
A calf must absorb 10 grams of IgG per liter of blood plasma to achieve passive transfer, Fox says.
Here’s how much IgG must be absorbed by the 90-pound calf from Step 1:
3.7 L of plasma volume x 10 g per L = 37 g of IgG that needs to be absorbed.
Don’t confuse this number with the amount of antibodies that you must feed — 100 grams or more —- to achieve passive transer. Due to absorption inefficiency, a calf only absorbs between 35 percent and 50 percent of the antibodies fed immediately after birth, Fox says. Absorption efficiency declines dramatically during the next few hours.
Test the cow’s colostrum.
An on-farm IgG test quickly tells you how much immunoglobulin the dam’s colostrum contains. If you don’t have such a test or are not using a colostrometer, use 50 grams of IgG per liter of colostrum — the amount produced by a typical Holstein cow. Save this information for the next step.
Will the calf achieve passive transfer?
This step takes what you’ve learned in Steps 1, 2 and 3 and ties it all together. The end result is that you will know whether or not the calf will achieve passive transfer of immunity based on the quality and quantity of colostrum fed.
To do that, examine the scenarios on the next page.
Example 1: Two quarts is a gamble
If you choose to feed only 2 liters, or roughly 2 quarts of colostrum at birth, passive transfer will be achieved only if colostrum quality is good and the calf absorbs a sufficient amount of IgG — and you won’t know that until you take a blood sample for serum total protein or serum IgG. That will become apparent as you work through the following calculation that uses high-quality colostrum and good absorption.
50 g IgG per L colostrum x 2 L fed = 100 g of IgG fed
100 g of IgG x 50 percent efficiency of absorption
= 50 g absorbed
This exceeds the 37 grams of IgG identified in Step 2, so the calf achieves passive transfer. However, if absorption is only 35 percent, passive transfer can fail.
100 g of IgG x 35 percent efficiency of absorption
= 35 g absorbed
An absorption efficiency of 50 percent is most likely to occur immediately after birth. So, expect only 35 percent absorption most of the time.
Example 2: Four quarts is best
Now, if you increase the volume fed to 4 liters, or roughly 4 quarts of colostrum, the calf is more likely to acquire sufficient immune protection.
50 g IgG per L colostrum x 4 L fed = 200 g of IgG fed
Even at only 35 percent absorption, the calf still absorbs enough immunoglobulin for passive transfer.
200 g of IgG fed x 35 percent efficiency of absorption = 70 g absorbed
This exceeds the 37 grams of IgG identified in Step 2, so the calf achieves passive transfer.
One caution: A larger volume of colostrum does not compensate for poor-quality colostrum. If the calf’s absorption efficiency is on the low end of the range, say 35 percent, you can still run into trouble. The following example, which uses colostrum containing only 25 grams of IgG per liter, illustrates just that.
25 g IgG per L colostrum x 4 L fed = 100 g of IgG fed
100 g of IgG fed x 35 percent efficiency of absorption = 35 g absorbed
That’s just shy of the 37 grams needed by a 90-pound calf, but why gamble? The calf’s immune status and subsequent health are on the line. Make it your goal to feed 4 quarts of high-quality colostrum immediately after birth.