Immune System Background

The immune system has 2 divisions – an innate system that responds in a non-specific way to challenges and an acquired or adaptive immune system.

The adaptive/acquired/specific immune system responds after natural infection or vaccination to components of pathogens that are called antigens – substances that cause the body to produce antibodies.

The body’s response to antigens is a complex process that results in developed B and T cells (2 types of leukocytes, a class of white blood cells) that remember specific pathogens and help either prevent reinfection or mount a rapid response to reinfection.  It  takes 10 to 20 days for an initial response by the adaptive immune system – this is why colds tend to last 10 to 14 days.

Antigen stimulated B cells become either plasma cells that produce antibodies currently or memory cells that can survive for many years. Antibodies circulate in body fluids and fight infection by binding to the same pathogens that originally stimulated their production.  When antibodies bind pathogens, they can keep them from entering cells,  can activate  substances such as complement to kill bacteria and can recruit other pathogen fighting cells.

Passive Transfer and its Failure

Passive transfer is usually referred to as the process of receiving antibodies from the mother to protect the newborn early in life – especially during the first weeks before the newborn can make its own antibodies.

Humans newborns receive antibodies from the mother via the placenta. Farm mammals have different types of placentas that prevent such a transfer. For them, passive transfer is via the antibodies and other substances produced in colostrum, or first milk.

Blood transfusions containing antibodies are another form of passive transfer.

Failure of Passive Transfer and Its Consequences

When there is failure of passive transfer (“FPT”), there is a greater risk of illness and death.  Calves with FPT are twice as likely to die (J Vet Intern Med 14:569-77).  FPT is also associated with lower long term milk production.

FPT remains common.  19% of all calves tested on 394 US farms s (J Dairy Sci 2009 92:3973-80) had FTP and 41% of farms had a least one calf with FPT.  FPT was most common in herds of 25 to 74 cows.  Farms that did not monitor serum proteins (IgGs) were more than 13 times more likely to have FPT.  Prolonged dystocia calves with delayed veterinary assistance were 2.6 times more likely to have FPT.

Measuring Passive transfer

While there are many different types of antibodies or immunoglobulins, the most important for evaluating passive transfer is IgG (Immunoglobulin Class G).

Calf serum IgG levels of 10 mg/ml at 1 to 7 days of birth are generally considered protective (BAMN1 2001 & Vet Intern Med 10:304-7).

Historically measurement at 24 hours was set as a standardized time for measurement to make  for herd health statistics comparable.  The gold standard for accurate measurement is radial immunodiffusion (“RID”), a test that takes 24 to 48 hours to produce a result and is relatively expensive.  By the time a an RID test result was received it was too late for any intervention.

Easier to use earlier tests could make intervention possible.

How long can IgGs be Absorbed?

Intestinal “closure” is said to occur when such IgGs and other protective molecules  can no longer be absorbed.  Closure occurs, on average, at 24 hours, with a standard deviation of 4 hours (J Dairy Sci 62:1632-8). Closure is earlier in animals fed earlier and delayed when initial feeding is delayed.  When colostrum is fed at birth, closure averages around 21-22 hours.  If colostrum feeding is delayed, closure can be delayed to about 30 hours, sometimes more(Ibid).  One study found hypoxic calves to have closure delayed as long as 40 hours (J Dairy Sci 74:1953-6).

Delays in closure offer an opportunity to improve outcomes, if IgG levels can be tested before closure occurs and while absorption is still possible.

With early colostrum feeding the rate of absorption is fastest in the first 4-8 hours after birth and then decreases.  From 12 – 20 hours absorption is half the rate as during the first 8 hours (Ibid) and the rate continues to decrease (J Dairy Sci 62:1632-8).

With delayed feeding, the time for rapid absorption can be at a later time (J Dairy Sci 74:1953-6). Respiratory or metabolic acidosis due to prolonged calving can delay absorption in the first 18 hours postpartum but those animals typically have increased absorption after a 2nd colostrum feeding.

Serum IgG levels continue to rise after intestinal closure

IgG absorbed by enterocytes enter the lymphatic system first and only later are distributed into the bloodstream and can be measured.  An average curve with an intestinal closure of 24 hours will usually show a serum IgG peak at about 32 hours after birth (J Dairy Sci 62:1632-8).

Factors Affecting IgG Absorption from Colostrum

Serum IgG levels in the calf are related to quantity and quality of colostrum, when the colostrum is fed and the rate a calf can absorb the protective substances in it.

Studies of absorption have led to a recommendation that more than 100 g. of colostral IgG be fed early in life. Studies of quality have led to a further recommendation that this is best accomplished by feeding 4 liters of colostrum to decrease the risk of FPT (J Vet Intern Med 14:469-77).

Timing of colostrum and testing for IgG

A study in Jerseys found that 4 liters or 2 liters of high quality (84 g/L) colostrum or 4 liters of low quality (31 g/L) colostrum fed at birth all generated of IgG over 15 mg/ml when tested at 12 hours.  2 liters of low quality colostrum fed at birth resulting in IgG levels of ~7.7 mg/ml at 12 hours (J Dairy Sci. 2009 88:296-302).

The 2 groups that received only 2 liters of colostrum at birth were fed a further 2 liters of the same quality colostrum at 12 hours. Both of these groups had average IgG levels at 24 hours that were 50% higher than at 12 hours.  In both groups IgG levels increased ~50% from 12 to 24 hours, largely protecting the low quality group.

Are Jerseys and Holsteins comparable?

A study colostral IgG by breed found that the average concentration in Holsteins to be ~56g/L (J Dairy Sci 64:1727-30). This was lower than other breeds, but 80% higher than the low quality (31 g/L) colostrum concentration used in the Jersey study described above.

 Can colostrum be easily tested at 12 hours after birth?

At least one company has introduced an instrument based test, which may be best suited to use by veterinarians.

The ZBx test is a simple test that requires one drop of whole blood or serum with all the reagents contained within the cartridge.  No instrument is required and results are ready within 15 minutes.

1Bovine Alliance on Management and Nutrition