Failure of Passive Transfer in Foals

Failure of passive transfer in foals. Learn the risk factors, consequences, clinical signs, treatment, and prevention.

Bringing a new foal into the world is exciting—but it can also be stressful when you’re constantly wondering if they’re getting the immunity they need to stay healthy. Failure of passive transfer (FPT) is one of those silent problems that can turn a normal newborn into a critical case overnight. Knowing how to recognize and prevent it can make all the difference in keeping your foal thriving from day one.

Failure of passive transfer (FPT) is inadequate ingestion or absorption of colostral antibodies (one in particular is immunoglobulin G; IgG) in the first 24 hours of life, resulting in insufficient IgG concentrations in the foal.

Foals are born with a naïve immune system. They rely heavily on the mare’s colostrum to provide passive immunity, through the transfer of antibodies (immunoglobulins). This passive immunity is crucial for protection against disease in the neonatal period.

The equine placenta type is diffuse epitheliochorial, which means there is no transplacental transfer of antibodies to the foal in utero. Therefore, ingestion and absorption of immunoglobulin G-rich colostrum is the only route of passive transfer of immunity in foals.

The foal’s gastrointestinal tract (GIT) features specialized cells capable of absorbing antibodies through a process known as pinocytosis. The time during which the GIT is considered “open”. However, the window of GIT absorptive capacity narrows progressively over the first 12 to 24 hours of life. The GIT is considered closed once it is incapable of absorbing antibodies.

Maximal absorptive capacity occurs immediately after birth and within the first 3 to 6 hours. Therefore, making the first 6 hours after birth the optimal time frame for the foal to ingest colostrum. By 20 hours after birth, absorption efficiency drops to just 1 percent, and by 24 hours, the GIT is incapable of antibody absorption.

Failure of passive transfer (FPT) significantly increases the risk of infectious diseases in neonatal foals, potentially culminating in sepsis and mortality. The foal will not show clinical signs with Inadequate serum IgG concentrations alone. However, once infection develops, characteristic clinical signs emerge. This includes weakness, fever, lack of nursing, spending more time lying down, diarrhea, and/or swollen joints. FPT is a well-established predisposing factor for bacterial infections manifesting within the first two weeks of life. Some of these diseases include septicemia, septic arthritis, pneumonia, and enteritis, each of which can rapidly escalate without timely intervention.

Fortunately, FPT is both preventable and treatable. Substantially mitigating the incidence of neonatal infections, though vigilant management remains essential. Effective strategies center on proactive education. Fostering awareness of FPT, identifying key risk factors (such as premature lactation or dystocia), implementing prophylactic measures like colostrum supplementation, and routinely testing IgG levels in every foal.

Failure of passive transfer in neonatal foals arises from several broad categories of contributing factors, each underscoring the delicate interplay between maternal colostrum production, foal nursing behavior, and intestinal absorption. These include:

• Inadequate colostrum quality: The mare produces colostrum with suboptimal IgG concentrations, compromising the foundational immune support available to the foal.
• Premature loss of colostrum: The mare leaks or expels colostrum prior to nursing (often due to premature lactation), rendering insufficient volumes accessible to the foal.
• Insufficient intake within the critical window: The foal fails to consume an adequate volume of colostrum during the narrow time frame, during intestinal absorption capacity.
• Impaired gastrointestinal absorption: The foal’s gastrointestinal tract does not effectively uptake colostral antibodies, potentially due to physiological immaturity or underlying dysfunction.
• Accelerated IgG degradation in compromised foals: Sick neonates experience heightened catabolism of circulating IgG.

A 12-hour-old colt being assessed for health and IgG concentration.

While any neonatal foal is susceptible to failure of passive transfer, routine evaluation of serum IgG levels at 12 to 24 hours of age is a cornerstone practice ensuring early detection and intervention. Certain scenarios, however, elevate the risk profile, warranting proactive identification and prophylactic treatment to provide passive immunity before infection occurs.

• High-risk situations encompass the following:
• Maternal factors compromising colostrum availability or quality: Including premature lactation (e.g., secondary to placentitis, twins, premature placental separation) or low IgG concentrations in colostrum, which can be assessed using a brix refractometer or a colostrometer.
• Dystocia or traumatic delivery: Prolonged or assisted births that delay nursing or result in an abnormal foal that does not nurse.
• Neonatal behavioral or neurological impairments: Such as dummy foal syndrome (neonatal maladjustment syndrome).
• Delayed or absent nursing: For any reason, including environmental stressors, maternal rejection, or neonatal factors, underscores the need for assisted feeding.
• Physical impediments to nursing: Foals unable to stand due to congenital limb deformities, such as flexural or angular contractures (e.g., contracted tendons).
• Perinatal illness or abnormality: Any foal presenting as weak, hypoxemic, or otherwise compromised at birth.
• Orphaned or rejected foals: Those necessitating immediate alternative colostrum sources like stored/banked frozen colostrum.

By recognizing that a foal is at risk of failure of passive transfer, a plan can be implemented. The goal in mind is to prevent FPT and infectious disease.  

The treatment of FPT in foals depends on several factors. For the purpose of this blog, only the treatment methods of supplying immunoglobulins (IgG; antibodies) will be covered.  

Equine colostrum is the optimal and primary treatment. Colostrum has many benefits (local and systemic) and is a less expensive means of treatment.

If FPT can be predicted, administer colostrum during the optimal time of GIT absorption capacity. Colostrum can be obtained by milking the mare or thawing out stored frozen high-quality colostrum. Administer the colostrum to the foal via a nasogastric tube (your veterinarian will perform this).

You can bottle feed colostrum using a small lamb’s nipple. Only attempt bottle feeding if the foal has a strong suckle and is not weak. Place the bottle in a position that mimics the mare’s udder position. This way, the foal has its head and neck in a normal position. This might help reduce the risk of aspiration of milk. Weak or premature foals are at risk of aspiration pneumonia if bottle-fed.

Example bottle-feeding regime: Give 4-6 oz of colostrum divided into 2 feedings every hour for 6-8 hours. The ability to administer this volume of colostrum will depend on the foal’s mentation, energy level, ability to swallow, and strength of suckle reflex. Never force the foal to drink colostrum, or you will likely cause aspiration pneumonia.

If equine colostrum is not available, concentrated equine serum products such as Seramune Oral can be used. This product is not a reliable means of increasing the foal’s IgG levels to normal values (>800mg/dl). The most likely reason is the challenge of administering a high enough dose to the foal. This product should not replace equine colostrum or plasma. However, it could provide some level of antibody protection until the foal is evaluated by the veterinarian.

A plasma transfusion being performed in a 12-hour-old colt to treat failure of passive transfer.

Equine plasma is the treatment of choice in a foal that is over 12 hours old. There are exceptions to this as every foal situation is different. Discuss with your veterinarian for the best course of action. Over 12 hours of age, the foal’s gastrointestinal tract has significantly reduced capacity to absorb immunoglobulins (IgG). If colostrum is available, it may be administered orally in additional to intravenous plasma to provide localized gastrointestinal benefits.

Equine plasma has a high concentration of IgG and must be administered by a veterinarian. IgG levels should be reassessed at 24 hours to confirm adequate levels in the foal. If IgG levels remain insufficient, additional plasma transfusions may be performed.

This is the same colt, 48 hours of age, IgG concentrations corrected to normal levels, and the colt was in good health.

Effective management, informed decision-making, and robust support from farm staff and veterinary professionals are essential to reduce the risk of Failure of Passive Transfer in neonatal foals. The following practices promote optimal health outcomes:

1. Risk Assessment and Preparation: Identify foals at risk of FPT and ensure a supply of high-quality colostrum is readily available.
2. Monitoring Foaling: Observe the foaling process closely to confirm that the foal nurses within two hours of birth and exhibits a strong suckle reflex.
3. Colostrum Administration: For foals deprived of colostrum, administer high-quality colostrum within 4–6 hours of birth, ideally within 3 hours, to maximize immunoglobulin absorption.
4. Veterinary Evaluation: Arrange for a veterinarian to perform a neonatal examination and assess IgG levels at 12 hours of age. If a foal appears weak or is not nursing, seek immediate veterinary evaluation.
5. Colostrum Quality Assessment: Evaluate the mare’s colostrum quality using a Brix refractometer or equine colostrometer. A Brix reading of 20–30% indicates adequate colostrum quality, while a reading above 30% signifies excellent quality. For an equine colostrometer, a specific gravity greater than 1.060 is considered adequate.

By implementing these proactive measures, farm managers and veterinarians can significantly reduce the incidence of FPT and support the health and development of neonatal foals.

-Failure of passive transfer (FPT) is inadequate ingestion or absorption of colostral antibodies (one in particular is immunoglobulin G; IgG) in the first 24 hours of life, resulting in insufficient IgG concentrations in the foal.

-Idea time to administer colostrum- within 3 hours of birth– This is when maximal gastrointestinal tract absorptive capacity of immunoglobulins occurs.

-FPT significantly increases the risk of infectious disease in neonatal foals in the first 2 weeks of life and can lead to death.

-Clinical signs include weakness, fever, lack of nursing, spending more time lying down, diarrhea, and/or swollen joints.

-Foals at risk of FPT are foals separated from their dam and/or deprived of colostrum for any reason, foals abnormal since birth, or foals born to dystocia (this is not an exclusive list).

-Treatment- equine colostrum or equine plasma.

-Prevention- effective management, IgG checks at 12 hours of birth (can be sooner at 8 hours of birth), prophylactically administer high-quality colostrum to foals predicted to be at risk of FPT.

Smith B.P., Van Metre D.C., Pusterla N. (2020). Large Animal Internal Medicine. 6th ed. Elsevier. pp. 1734-1738.

Madigan J.E. (2013). Manual of Equine Neonatal Medicine. 4th ed. Live Oak Publishing. pp. 29-35.

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