section name header

Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Inadequate passive immunity in neonates evidenced by abnormally low concentrations of immunoglobulins in serum at >18 h of age. Normal, healthy foals that ingest an adequate volume of high-quality colostrum and absorb the immunoglobulins have serum IgG >1500 mg/dL (>15 g/L) and often >2000 mg/dL (>20 g/L)
  • IgG concentrations in serum <800 mg/dL (<8 g/L) represent FTPI. IgG concentrations in serum <400 mg/dL (<4 g/L) represent complete FTPI. IgG concentrations in serum of 400–800 mg/dL (4–8 g/L) represent partial FTPI

Pathophysiology!!navigator!!

  • Because of diffuse epitheliochorial placentation in mares, immunoglobulins do not cross the placenta during gestation
  • Foals are born immunologically competent but without significant concentrations of immunoglobulins in the blood. Humoral immunity is therefore dependent on absorption of colostral immunoglobulin. Autogenously produced gamma-globulins do not reach adult levels until about 4 months of age
  • Immunoglobulins are concentrated by selective secretion in the mare's udder during the last 2 weeks of gestation. Specialized epithelial cells in the foal's small intestine pass macromolecules via pinocytosis into local lacteals and, subsequently, into the blood. These cells are replaced by nonspecialized intestinal epithelial cells; maximal absorption occurs after birth, decreases in efficiency by 12 h, and is gone by 24 h
  • Foals require approximately 2 g/kg of IgG to achieve a serum IgG concentration of 2000 mg/dL (2 g/L)
  • Foals (45 kg) need to ingest >1.5 L of acceptable quality colostrum to have a reasonable expectation of serum IgG > 800 mg/dL (>8 g/L)

Systems Affected!!navigator!!

FTPI places the foal at risk of systemic illness associated with infectious, usually bacterial, disease, with localization in the lungs (pneumonia), gastrointestinal tract (diarrhea), or joints (septic arthritis).

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

  • FTPI has been reported to occur in 3–24% of otherwise normal Thoroughbreds, Standardbreds, and Arabians in the USA, UK, and Australia
  • Out of a large population of neonatal foals, 61% of hospitalized foals had FTPI in a recent study

Signalment!!navigator!!

Breed Predilections

N/A

Mean Age and Range

Affected foals are neonates, although signs of disease secondary to FTPI might not develop for days to weeks.

Predominant Sex

N/A

Signs!!navigator!!

General Comments

  • There are no clinical signs pathognomonic of FTPI because it is a measure of the strength of the immune system, not a pathologic process
  • Foals with FTPI are at increased risk of developing sepsis, pneumonia, septic arthritis, diarrhea, and omphalophlebitis, among other infectious diseases. The signs are typical of these diseases

Historical Findings

  • Foals born to mares >15 years of age are at increased risk
  • Premature lactation diminishes the quantity of colostrum
  • Mares kept on endophyte-infected tall fescue pasture or hay often fail to produce colostrum and milk
  • Foals must ingest an adequate amount of colostrum within 12–18 h of birth, preferably within 3 h, in order to absorb sufficient IgG. Foals that are slow to stand and nurse, or that are unable to stand and nurse, are unable to ingest colostrum

Physical Examination Findings

  • Normal unless they develop infectious disease
  • Many foals with partial FTPI kept in optimal conditions with environmental cleanliness and good farm management do not become sick

Causes!!navigator!!

  • Insufficient volume of colostrum, loss of colostrum through premature lactation, or colostrum that contains insufficient amounts of immunoglobulins
  • Colostrum with a specific gravity <1.060 (as measured with a colostrometer) has IgG concentration <3000 mg/dL (<30 g/L) and is associated with an increased risk of FTPI
  • Failure of the foal to nurse by 3–6 h after birth is associated with complete or partial FTPI; foals that fail to nurse by 12 h usually have complete FTPI

Risk Factors!!navigator!!

  • Illness or chronic debilitating disease in the mare during gestation, mares >15 years, mares that lactate prematurely, mares with poor mothering behavior
  • Foals born in cold, overcast climates have an increased incidence compared with foals born in climates with more total solar radiation
  • Premature foals and foals from prolonged gestation
  • Any foal that is weak or otherwise poorly adapted to extrauterine life

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

CBC/Biochemistry/Urinalysis!!navigator!!

Foals with serum total protein concentrations <4.0 g/dL are 2.5 times more likely to have FTPI. However, unlike the situation in calves, this is not a good screening test for FTPI in foals. A CBC should be evaluated in any foal with FTPI to evaluate for evidence of systemic disease.

Other Laboratory Tests!!navigator!!

  • Serum IgG is detectable at 6 h of age in foals that nursed by 2 h and is almost maximal at 12–16 h of age in these foals
  • The gold standard for measurement of serum IgG concentrations is the SRID. However, this test requires up to 24 h to complete and is therefore of minimal clinical utility. The turbidometric immunoassay is more rapid and correlates highly with the SRID
  • An ELISA kit (CITE Foal IgG Test Kit, IDEXX Laboratories, Westbrook, ME) uses serum, plasma, or whole blood and provides semiquantitative measurement of IgG. The test has approximate sensitivity and specificity of 53% and 100%, respectively
  • The zinc sulfate turbidity test has sensitivity and specificity of 97% and 57%, respectively, making a good screening test
  • The glutaraldehyde clot test has sensitivity and specificity of 100% and 59%, respectively, making it also a good screening test
  • The latex agglutination test (Foalcheck, Centaur, Overland Park, KS) estimates the amount of IgG from the degree of agglutination of serum or blood with latex beads coated with anti-equine IgG antibody. The test has low sensitivity and specificity (72% and 79%, respectively), so it is not recommended

Diagnostic Procedures!!navigator!!

Based upon the presence of signs of disease.

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

  • Raise the serum IgG concentration to at least 800 mg/dL (8 g/L) for a foal that has any risk factors for sepsis
  • Foals with serum IgG 400–800 mg/dL (4–8 g/L) may not require plasma transfusion if they are on a well-managed farm and are at low risk of sepsis

Appropriate Health Care!!navigator!!

  • Colostrum and plasma can be given in the field, but if signs of septicemia or other systemic illness are apparent referral is recommended
  • Any neonatal foal with FTPI should be maintained in sanitary environmental conditions

Nursing Care!!navigator!!

  • Foals <12 h of age—oral administration of colostrum with a specific gravity >1.060 is the preferred treatment. 2–4 L of colostrum administered in 500 mL increments every 1–2 h during the first 6–8 h of life is desirable. Administration of bovine colostrum results in equine-specific passive immunity that is less than optimal and is not recommended
  • In foals >12 h, adequate absorption for optimal IgG concentrations is unlikely and serum or plasma should be administered IV
  • Concentrated equine serum and lyophilized equine immunoglobulins are not recommended
  • Plasma—use of commercial frozen plasma is preferred. Fresh plasma can also be harvested from the mare or another horse with neither lysins nor agglutinins to equine RBC antigens
  • Plasma should be transfused at a rate of 40 mL/kg to foals with serum IgG <400 mg/dL and at a rate of 20 mL/kg to foals with serum IgG of 400–800 mg/dL. Generally, a 45 kg foal with IgG <400 mg/dL will require 2 L of plasma, and a foal with serum IgG of >400 mg/dL but <800 mg/dL will require 1 L of plasma. Most commercially available hyperimmune plasma products contain an IgG concentration of 1500–2500 mg/dL (15–25 g/L). Measurement of serum IgG should be performed after transfusion (as soon as 30–90 min post transfusion) to confirm that adequate IgG concentrations have been achieved
  • Administer IV plasma through an inline filter. Thaw frozen plasma slowly in a water bath at 39–45°C (102–113°F), and warm to at least 20°C before administration. The initial plasma or serum infusion should be slow and the foal observed for adverse reactions. Subsequently, the infusion may be given at 20–30 mL/kg/h

Client Education!!navigator!!

Treatment of FTPI should be pursued as there is evidence of higher rates of nonsurvival in foals with any degree of FTPI compared with those with adequate IgG concentrations.

Medications ⬆ ⬇

Outline

MEDICATIONS

Contraindications!!navigator!!

  • No contraindications to commercially available, fresh-frozen plasma
  • Use of fresh plasma from horses with agglutinins or lysins to equine RBC carries a risk for neonatal isoerythrolysis

Precautions!!navigator!!

  • Frozen plasma thawed at too high a temperature or in a microwave oven contains denatured proteins that can subsequently cause severe reactions during transfusion
  • If adverse reactions occur during administration of plasma or serum products, discontinue the infusion until signs abate, and then continue the infusion at a slower rate. If adverse reactions continue, terminate the infusion

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Foals with sepsis appear to have a reduced half-life of exogenous IgG and may need multiple transfusions to maintain serum concentrations above 800 mg/dL (8 g/L).

Prevention/Avoidance!!navigator!!

  • Ensure that newborn foals are able to stand and nurse within 2–3 h of birth. If unable to nurse on own, supplement with at least 1.5 L good quality colostrum via bottle or nasogastric tube (in 500 mL increments)
  • If the mare has dripped milk prior to delivery or has been exposed to fescue, the foal should receive a good quality colostrum or plasma transfusion shortly after birth

Possible Complications!!navigator!!

Foals with FTPI should be monitored for signs of sepsis.

Expected Course and Prognosis!!navigator!!

  • Foals with uncomplicated FTPI have an excellent prognosis with appropriate treatment
  • Complications with sepsis will lower the prognosis

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Diseases!!navigator!!

  • Neonatal sepsis
  • Perinatal asphyxia syndrome

Pregnancy/Fertility/Breeding!!navigator!!

Ensure pregnant mares are on an appropriate vaccination schedule.

Abbreviations!!navigator!!

  • ELISA = enzyme-linked immunosorbent assay
  • FTPI = Failure of transfer of passive immunity
  • IgG = Immunoglobulin G
  • RBC = red blood cell
  • SRID = single radial immunodiffusion assay

Internet Resources

Case File: Failure of Passive Transfer in a Foal. http://csu-cvmbs.colostate.edu/Documents/equine-medicine-surgery-case-study-2013-01-ERL.pdf

Suggested Reading ⬆ ⬇

Giguère S, Polkes AC. Immunologic disorders in neonatal foals. Vet Clin North Am Equine Pract 2005;21(2):241–272.

Liepman R, Dembek K, Slovis N, et al. Validation of IgG cut-off values and their association with survival in neonatal foals. Equine Vet J 2015;47(5):526–530.

Author(s) ⬆

Author: Rachel S. Liepman

Consulting Editor: Margaret C. Mudge

Acknowledgment: The author and editor acknowledge the prior contribution of Kenneth W. Hinchcliff.