Failure of Passive Transfer

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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.

    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 – the foal receives no colostrum – or it can be partial – the foal received poor quality colostrum. Colostrum is the first milk that the mare makes. She begins making it about one month before the foal is to be born.

    During the process of producing this milk, antibodies from the mare's blood are selectively filtered and concentrated into the mammary tissue of the udder. It is generally thicker in nature and yellow tinged compared to regular mare's milk. Specific antibodies called immunoglobulins are found in the milk. The predominant immunoglobulin is IgG, followed by IgM. A batch of colostrum is only made once per pregnancy and disappears in the first couple days as the foal suckles.

    The importance of the foal receiving colostrum centers around the fact that the foal is born essentially devoid of his own protective immunoglobulins. This occurs in many of our domestic species because of placental differences and thickness. In the human placenta there is only one layer of tissue separating the maternal blood supply from the fetal blood supply. Immunoglobulins, which are large molecules, can easily cross this distance. In contrast, the mare's placental has six layers of tissue separating the maternal blood flow from the fetal blood flow. The immunoglobulins are unable to penetrate these layers. Without protective immunoglobulins the newborn foal is highly susceptible to infection from even normal environmental bacteria.

    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. The foal's intestine is "open" to absorb the large immunoglobulins for a limited amount of time. The intestinal tract begins to lose this ability around 12 hours of age and it is usually totally gone by 24 hours of age. Foals greater than one day of age are unable to absorb immunoglobulins from even the richest colostrum.

    Colostral "richness" in terms of the amount of immunoglobulins present varies from mare to mare and at 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 colostrum quality. Mares over 15 years of age have been reported to have a decreased quality of colostrum.

    Risk factors for failure of passive transfer of colostral immunoglobulins include prematurity or postmaturity. Because the mare only makes colostrum once, any leakage of milk from the mare before the foal is born should be taken as a matter of grave concern. In premature lactation the mare may never build up good concentrated colostrum or she may lose the best portion of the colostrum, diluting the rest out with normal milk that is practically devoid of immunoglobulins. If the mare rejects the foal or is aggressive toward him, the foal may also be deprived of colostrum. Other risk factors include problems that may occur in the foal to prevent him from nursing. If the foal is weak at birth or has limb deformities that prevent him from standing, the foal may also not receive adequate colostrum.

    The immunoglobulin level can be measured on the farm by the specific gravity of the colostrum. There is an instrument called a colostrometer, which simply measures the specific gravity of 5 mls of colostrum in a column of distilled water. The density of the colostrum is directly proportional to the amount of immunoglobulins present. A specific gravity of 1.060 is considered adequate for foal protection. Specific gravities over 1.080 are considered excellent. It is handy to have a way of measuring colostrum quality on breeding farms. Knowledge of which mares may have poor colostrum may help predict which foals are at risk for total or partial failure of passive transfer.

    Colostrum from mare's that have excellent specific gravities can be used to feed her own foal or saved for another foal that needs colostrum such as an orphan or a foal from a mare that leaked her colostrum out. In these mares you can allow her foal to nurse one teat while you milk the other. It is safe to save about 1 cup of this high specific gravity colostrum without depriving her own foal of the needed antibodies. The milked colostrum should be strained through a piece of cloth, such as gauze, to eliminate large dirt particles. It can then be placed into plastic containers or freezer bags and placed into the freezer. The container should be labeled with the name of the mare, the date and the specific gravity. It will remain good up to 1 year in the freezer.

    Some people feel that lack of colostrum is not the only cause of infection in foals. The fact that the intestine is "open" to absorb colostrum in the first hours after birth also means that it may be "open" to absorb more bacteria during this time. The act of eating hastens the closure of the intestine, therefore, receiving colostrum early not only provides immunoglobulins, it decreases the amount of time that bacteria can be absorbed. Some people advocate milking the mare immediately after the birth of the foal and bottle feeding him before he stands to expedite the process of intestinal absorption of colostrums and closure of the gut to harmful bacteria.

    The veterinary care of the foal with complete or partial failure of passive transfer begins with identifying the potential risk factors and performing a physical examination of the foal. If the foal is less than 12 hours of age and has not nursed then it is assumed that the foal has FPT and is in need of immediate colostrum. If a colostrometer is available then the mare's colostrum should be checked for quality. If a colostrometer is not available then the appearance of the colostrum is helpful. It should be thick, yellowish and sticky when it dries on your fingers. The mare should be milked out and the foal should be administered the colostrum by bottle. In weak foals or foals that don't have a suckle reflex, the colostrum should be administered by the veterinarian by stomach tube. Just syringing it into the foal's mouth is not adequate, and may result in aspiration (inhalation) of the milk. If the colostrum is not of good quality then another source of colostrum should be sought.

    The volume of colostrum needed obviously varies with the amount of immunoglobulins present in the 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.

    Other oral fluids should not be given before the colostrum administration because it will tend to "close" the intestine to immunoglobulin absorption sooner.

    The veterinarian can measure the amount of immunoglobulin absorption in foals by a simple blood test called a CITE test. The CITE test is a semi-quantitative test that will give a range of immunoglobulin levels in the foals blood. Adequate passive transfer is considered over 800 mg/dl of immunoglobulins. Complete FPT is considered less than 200 mg/dl. Partial FPT is anywhere in between. The advantage of this test is that it can be done on the farm and the results are known within 20 minutes. This allows the treatment for FPT to begin immediately if needed. Though waiting a day for the results in a normal foal is usually safe, it is not acceptable in a high-risk foal. A high-risk foal would be a foal that may not have received adequate colostrum for whatever reason.

    There are other tests that can be used to measure foal immunoglobulin levels. They include the zinc sulfate precipitation test, an agglutination test and an immunodiffusion test. All are adequate but the precipitation test takes 1 hour and the immunodiffusion test requires 12 to 24 hours before it can be read. The precipitation and the agglutination test are not as quantifiable as the CITE test.

    A high risk foal should have his immunoglobulin levels determined around 12 hours of age. It is important that the foal have at least 400 mg/dl at this time to provide him with some protection against the environmental bacteria. This allows time for the majority of absorption even though the foal will continue to absorb immunoglobulins for up to 24 hours. In a non- high-risk foal, it is usually safe to wait for 24 hours to test the level of immunoglobulin.

    If a foal has complete or partial failure of passive transfer at 12 hours of age you can still administer good quality colostrum and expect some absorption to take place. However after 12 hours of age the absorption 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.

    Your veterinarian can purchase frozen hyperimmune plasma or use a blood donor on the farm to harvest plasma. The commercially available plasma has the benefits that it can be stored for a year, it is from universal donors (that lack antibodies that would react with the foal's red blood cells) and that its immunoglobulin levels is higher than normal horses. It is also easier to administer, requiring only thawing in warm water. One should be careful not to thaw in a microwave or with boiling water. Too much heat will denature the immunoglobulins.

    Harvesting plasma from a local donor is more labor intensive. Two to four liters of blood must be collected from the donor horse. This blood must sit for 1 to 2 hours allowing the red blood cells to settle out. The plasma must be siphoned off sterilely. It is difficult to collect the plasma without some red cell contamination. Red cell contamination could result in sensitizing the foal to certain blood types, which may cause a problem if the animal ever needs a blood transfusion in the future. If the foal is a filly and bred later in life it is possible that she would develop colostral immunoglobulins against her own foal's blood.

    Generally an intravenous catheter is placed in a foal for the administration of the plasma. Plasma should be run through a filtered IV line in order to take out any fibrin another component of blood. The rate of plasma administration should not exceed 1 liter/hour. The foal should be monitored for any side effects. These might include trembling and an increase in heart rate. The rate of plasma administration should be slowed down until these side effects stop. The amount of plasma needed depends on the starting level of immunoglobulins that the foal has and the quality of the plasma. Generally 1 to 1.5 liters of high quality plasma is needed to bring a complete FPT foal up to adequate levels. A partial FPT may only require 0.5 liters of high quality plasma.

    At the present time, the quality of commercial plasma is not regulated by the FDA or USDA, as is the quality of approved drugs or vaccines. Quality can vary considerably without the consumer knowing. However, there are currently guidelines being established for regulations of these products, and greater consumer confidence can be expected once these regulations are put in place, in the next couple years.

    Follow-up

    The foal with failure of passive transfer should have his immunoglobulins re-checked after receiving a plasma transfusion to ensure that it has reached 800 mg/dl. Foals with septicemia as a result of their failure of passive transfer may require more plasma than non-infected foals. It appears that the immunoglobulins in these foals are used up more quickly in fighting the infections. Rechecking the immunoglobulins in these foals 4 to 5 days later may be important. Additional plasma may need to be administered.

    Colostral immunoglobulins begin to disintegrate as soon as they are absorbed. In normal foals they disappear from the blood stream around 2 to 3 months of age. As they disappear, the foal begins to make his own immunoglobulins. The foal reaches adult levels of immunoglobulins around 4 to 5 months of age.

    The foal with failure of passive transfer should have his immunoglobulins re-checked after receiving a plasma transfusion to ensure that it has reached 800 mg/dl. Foals with septicemia as a result of their failure of passive transfer may require more plasma than non-infected foals. It appears that the immunoglobulins in these foals are used up more quickly in fighting the infections. Rechecking the immunoglobulins in these foals 4 to 5 days later may be important. Additional plasma may need to be administered.

    Colostral immunoglobulins begin to disintegrate as soon as they are absorbed. In normal foals they disappear from the blood stream around 2 to 3 months of age. As they disappear, the foal begins to make his own immunoglobulins. The foal reaches adult levels of immunoglobulins around 4 to 5 months of age.

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