Immunoglobulins cannot traverse the placenta in cattle, so calves are born without any innate immune protection. To that end,
feeding of colostrum has received research attention, and a few important outcomes have surfaced. First, the quality of colostrum
fed to the calf should deliver IgG to attain a blood concentration of at least 10 mg/ml. This is equivalent to 1000 mg/dl.
Surveys comparing quality of colostrum indicate that we can expect Holsteins to produce colostrum with IgG content averaging
48 g/L. The range will be expected to vary between 20 and 100 g/L (BAMN, 2001).
In heat-stressed calves, absorption of IgG may not be adequate, so blood concentrations should be assayed periodically. The
current recommendation within the industry is to feed 4 L of colostrum within 30-60 minutes following birth. Feeding can
be with a bottle or esophageal feeder, but it is essential that the calf gets fed 4 L to receive optimal passive immunity.
Death rates are higher in calves with blood concentrations below the 10 mg/ml range. Unfortunately, about 40 % of calves receiving
colostrum are at risk because because their blood values fall below the threshold of 10 mg/ml (BAMN, 2001).
In past recommendations, it was suggested that colostrum be pooled, particularly from older cows with broader exposure to
pathogens, so a wide range of protection could be conveyed to calves not receiving sufficient volume/quality of colostrum
from their dams. With the knowledge that a primary vehicle of Johne's transmission is feeding colostrum from an infected/shedding
animal, pooling of colostrum is now discouraged. It is a good practice to keep some colostrum from older cows for deprived
calves, but batches should be segregated so "trace-back" is possible if a cow is ever suspect for Johne's.
On large dairies, it is becoming commonplace to pasteurize colostrums to kill the Johne's bacterium. This is the ideal situation.
There are also several powdered colostrums on the market, and USDA ensures that the quality conveys the 10 mg/ml concentration
to fed calves when product is reconstituted with water.
Since accelerated raising of heifers has been evaluated experimentally, research has extended that to intensive feeding of
calves prior to weaning, which obviously touches on management practices with colostrum, milk and milk replacers. Drackley
(2007) summarized where the industry currently stands with those practices. What is becoming clear is that feeding of 4 L
of high quality colostrum can have a profound effect on lactational performance of those animals as cows more than two years
later! To put that into context, we need to consider that the bovine mammary gland is not fully differentiated until birth
of the first calf. Therefore, there is a wide window in which we may be able to positively (or negatively) affect productive
potential of an animal commencing in utero and continuing out to approximately two years of age.