Failure of Passive Transfer

Failure of passive transfer (FPT) is defined as the failure of the foal to receive adequate colostrum from his dam. Failure of passive transfer can be complete where the foal receives no colostrum, or it can be partial where the foal received poor quality colostrum. Colostrum is the first milk that the mare makes. It contains protective antibodies for the foal.

When a foal is born he is essentially devoid of immunoglobulins (antibodies). It is only through ingestion and absorbing the immunoglobulins in colostrum that foals are protected against bacteria in the environment. Without protective immunoglobulins the newborn foal is highly susceptible to infection from environmental bacteria that would ordinarily not affect adult horses.

The timing at which the foal should ingest the colostrum and can absorb the immunoglobulins is crucial.

It is truly a race against the bacteria and the clock to protect the newborn foal from a life-threatening bacteria infection called sepsis. The foal needs to suckle the colostrum within 2 to 3 hours after birth. Any longer period without suckling endangers the foal both immunologically and nutritionally.

Colostral richness, in terms of the amount of immunoglobulins present, varies from mare to mare, and between different times of the year. Mares foaling in the spring and summer generally have a higher concentration of immunoglobulins than mares foaling in the winter. Sunny regions as opposed to overcast areas of the country appear to improve colostral quality. Older mares (over 15 years of age) have been reported to have a decreased quality of colostrum compared to younger cohorts.

Risk Factors

Prematurity (born at less than 320 days of gestation)

Postmaturity of the foals (greater than 360 days of gestation)

Leakage of milk from the mare before the foal is born (premature lactation)

Mare rejection of the foal or aggression toward him may also result in deprivation of colostrum

Other risk factors include problems that may occur in the foal to prevent it from nursing, such as weakness or limb deformities.

Foals with failure of passive transfer are more likely to develop septicemia, a life threatening bacterial infection. Septicemia can manifest as pneumonia, infected joints (septic arthritis), diarrhea and meningitis.

Diagnosis

The veterinary care of the foal with complete or partial failure of passive transfer begins with identifying the potential risk factors, performing a physical examination of the foal and conducting various blood tests. Treatment of failure of passive transfer depends on the foal's age. Specific tests include:

Measure immunoglobulin (IgG) levels in colostrum before the foal suckles.

Measure immunoglobulin (IgG) levels in high-risk foals at 12 hours of age. Adequate passive transfer is considered over 800 mg/dl of immunoglobulins (IgG). Complete FPT is defined as an IgG level under 200 mg/dl. Partial FPT is defined as measurements in the foal between 200 and 800 mg/dl IgG.

Measure immunoglobulin (IgG) levels in normal foals within 24 hours of birth.

Treatment

If the foal is less than 12 hours of age and has not nursed, then it is assumed that the foal has FPT and that it is in need of immediate colostrum.

For the average 100 pound foal approximately 32 ounces of adequate quality colostrum is needed. This amount can be divided into 3 equal feedings, given hourly for 3 feedings.

After 12 hours of age the foal's ability to absorb immunoglobulins is decreased and it is absent at 24 hours of age. In these cases it is important to provide the foal with immunoglobulins from another route. The only way to increase immunoglobulin levels after 24 hours of age is to administer plasma, the immunoglobulin-containing portion of blood, to the foals intravenously. It can also be given to the younger high-risk foal with complete or partial FPT as a supplement to colostrum administration.

Prevention

Not all foals with complete or partial failure of passive transfer will develop a life threatening infection. However, it has been shown that virtually all foals that develop life-threatening infections have at least partial failure of passive transfer. So making sure your foal gets good quality colostrum is the most important prevention.

Another way to decrease the chance of infection (septicemia) in the newborn foal, is to keep a clean foaling environment, especially when partial or complete failure of passive transfer is suspected. In fact, one study of a large well-managed breeding farm in Kentucky reported that foals with FPT did not have a higher rate of infection, in contrast to the common theory that all foals with FPT succumb to infection. What distinguished this farm was likely the immaculate sanitation of the stalls, and a policy that all foalings are attended by experienced foaling personnel. Foaling stalls were cleaned multiple times a day and freshly bedded. Foaling attendants made sure all foals stood and nursed within 2 to 3 hours of birth.
You can also decrease the amount of bacteria that the foal is exposed to by cleaning the stall and the mare immediately after the foal is born. Because the normal foal will suckle the walls, the mare's flank or her shoulder before finding the udder, cleaning the mare thoroughly may help. This has been shown to reduce the rate of transfer of Salmonella to foals, in one study. Special attention should be paid to cleaning the mare's udder, vulva and rear legs.