Newborn foals are born immunocompetent but with-out circulating immunoglobulins.1 It is crucial thatthe newborn foal receives immunoglobulins from themare’s colostrum to prevent infectious disease dur-ing the first few months of life. Healthy foals in-gesting good-quality colostrum will typically haveimmunoglobulin G (IgG) levels �800 mg/dl at 24 h oflife, which is considered adequate passive transfer ofimmunity.2 Failure of passive transfer (FPT) iscommonly defined as an IgG level �400 mg/dl after24 h of age.2 Partial failure of passive transfer(PFPT) is defined as an IgG level between 400 and800 mg/dl at 24 h of age.2
The incidence of FPT in foals is 10 –20%, and theincidence of PFPT in foals 17–19%.3–7 Risk fac-tors for FPT include ingestion of colostrum with alow level of immunoglobulin, failure to ingest asufficient quantity of colostrum, and failure toabsorb colostral immunoglobulins from the gastro-intestinal tract.2
Success of passive transfer should be measuredearly in life so that it is possible to intervene if
needed. An ideal screening test would be fast,quantitative, accurate, and inexpensive. Screeningtests available for evaluation of passive transfer aresingle radial immunodiffusion (SRID),1,8,9 glutaral-dehyde coagulation,9,10 zinc sulfate turbidity,8,11,12
latex agglutination,9,13,14 enzyme immunoas-say,15,16 turbidimetric assay (TIA),11,13,17,18 and se-rum total protein.1
The TIA is an excellent technique for screeningfoals for FPT. The TIA uses antibodies directedagainst an antigen to form immune complexes,which, in this case, is equine IgG.19 The amount ofanti-equine IgG antibody in the assay is constant,and therefore, the number of immune complexesthat form is proportional to the concentration ofantigen (equine IgG) in the foal blood sample. ATIA can yield quantitative results by evaluation ofthe turbidity of a test sample using a calibratedspectrophotometer.
The objective of this paper is to describe the use ofa new quantitative turbidimetric immunoassaya formeasuring concentrations of serum or plasma IgG inneonatal foals in veterinary practice.
AAEP PROCEEDINGS � Vol. 55 � 2009 45
MEDICINE—FOAL
NOTES
2. Materials and Methods
EquipmentApplication of this assay requires (1) a calibratedspectrophotometer and software,b (2) pipetter,c and(3) a test kitd (Fig. 1). The spectrophotometer usedfor this assay was originally designed to estimatesperm concentrations and was later adapted for es-timation of IgG. Consequently, this devise may al-ready be available at many breeding farms andveterinary clinics.
Accuracy of the AssayThe turbidimetric immunoassay has a high correla-tion to the single radial immunodiffusion test, whichis considered the gold standard for IgG determina-tion.18 At an IgG concentration of 400 mg/dl, TIAsensitivity was �90%, specificity was 99.1%, posi-tive predictive value was 98.1%, and negative pre-dictive value was 96.4%.18 At an IgG concentrationof 800 mg/dl, TIA sensitivity was �90%, specificitywas 70.5%, positive predictive value was 71.5%, andnegative predictive value was 91.1%.18 The assayreports values up to 2000 mg/dl. Samples withhigher IgG levels are reported as �2000 mg/dl.
How to Implement the Assay Into Your PracticeA blood sample should be collected for analysis ofadequate passive transfer as part of a foal wellnessexamination that is performed when the foal is12–24 h old. Almost all tests used to evaluate foalIgG concentrations are able to give satisfactory re-sults when the values are �800 mg/dl. However,the TIA stands out by being able to quantitativelydifferentiate IgG concentrations �800 mg/dl. TheTIA allows practitioners to make fast, accurate, andinformed decisions about how to treat FPT andPFPT.
3. Results
The turbidimetric immunoassay is used at our clinicto measure foal IgG levels at 12 and/or 24 h of life.The measurement of a foal’s IgG level at 12 h of ageallows for the ability to supplement with frozen-thawed colostrum through a bottle or nasogastrictube. This has decreased the need for administra-tion of IV hyperimmune plasma to foals for FPT orPFPT. Any foal at 12 h of age with an IgG concen-tration �400 mg/dl is routinely administered frozen-thawed colostrum or an equine IgG producte bynasogastric tube. Foals with an IgG level between400 and 800 mg/dl are also often administered fro-zen-thawed colostrum or an equine IgG product bynasogastric tube.
The use of the turbidimetric immunoassay in ourclinic has helped to improve the care for the newbornfoal by being able to accurately diagnose and treatFPT. A comparison of the results of TIA and SRIDtests is seen in Table 1. A foal born at our clinicwas examined at 12 h of age during a routine well-ness exam. From the TIA, it was observed that thefoal had PFPT (472 mg/dl). Frozen equine co-lostrum and an equine IgG producte were adminis-tered by nasogastric tube. A second blood samplecollected at 24 h of age showed a blood IgG value of871 mg/dl. All blood samples were subsequentlysubmitted for SRID test.
4. Conclusion
The turbidimetric immunoassay is a rapid, quanti-tative, and accurate technique to evaluate foal IgGlevels. The use of the turbidimetric immunoassayin our clinic has led to a higher level of care fornewborn foals through early detection and more sen-sitive monitoring of FPT or PFPT.
Fig. 1. Equipment necessary to perform the turbidimetric immunoassay.
46 2009 � Vol. 55 � AAEP PROCEEDINGS
MEDICINE—FOAL
References and Footnotes1. Davis R, Giguere S. Evaluation of five commercially avail-
able assays and measurement of serum total protein concen-tration via refractometry for the diagnosis of failure ofpassive transfer of immunity in foals. J Am Vet Med Assoc2005;227:1640–1645.
2. Barrington GM, Johnson JR. Immunologic disorders.In: Smith BP, ed. Large animal internal medicine, 4th ed.Philadelphia: Mosby, 2008;1667–1671.
3. Clabough DL, Levine JF, Grant GL, et al. Factors associ-ated with failure of passive transfer of colostral antibodies inStandardbred foals. J Vet Int Med 1991;5:335–340.
4. Erhard MH, Luft C, Remler HP, et al. Assessment of colos-tral transfer and systemic availability of immunoglobulin Gin newborn foals using a newly developed enzyme-linkedimmunosorbent assay (ELISA) system. J Anim PhysiolAnim Nutr (Berl) 2001;85:164–173.
5. LeBlanc MM, McLaurin BI, Boswell R. Relationshipsamong serum immunoglobulin concentration in foals, colos-tral specific gravity, and colostral immunoglobulin concentra-tion. J Am Vet Med Assoc 1986;189:57–60.
6. Perryman LE, McGuire TC. Evaluation for immune systemfailures in horses and ponies. J Am Vet Med Assoc 1980;176:1374–1377.
7. Tyler-McGowan CM, Hodgson JL, Hodgson DR. Failure ofpassive transfer in foals: incidence and outcome on fourstuds in New South Wales. Aust Vet J 1997;75:56–59.
8. Rumbaugh GE, Ardans AA, Ginno D, et al. Measurement ofneonatal equine immunoglobulins for assessment of colostralimmunoglobulin transfer: comparison of single radial im-munodiffusion with the zinc sulfate turbidity test, serumelectrophoresis, refractometry for total serum protein, andthe sodium sulfite precipitation test. J Am Vet Med Assoc1978;172:321–325.
9. Clabough DL, Conboy HS, Roberts MC. Comparison of fourscreening techniques for the diagnosis of equine neonatalhypoglobulinemia. J Am Vet Med Assoc 1989;194:1717–720.
10. Beetson SA, Hilbert BJ, Mills JN. The use of the glutaral-dehyde coagulation test for detection of hypogammaglobuli-naemia in neonatal foals. Aust Vet J 1985;62:279–281.
11. Bauer JE, Brooks TP. Immunoturbidimetric quantificationof serum immunoglobulin G concentration in foals. Am JVet Res 1990;51:1211–1214.
12. LeBlanc MM, Hurtgen JP, Lyle S. A modified zinc sulfateturbidity test for the detection of immune status in newlyborn foals. J Equine Vet Sci 1990;10:36–39.
13. Kent JE, Blackmore DJ. Measurement of IgG in equineblood by immunoturbidimetry and latex agglutination.Equine Vet J 1985;17:125–129.
14. Morris DD, Meirs DA, Merryman GS. Passive transfer fail-ure in horses: incidence and causative factors on a breedingfarm. Am J Vet Res 1985;46:2294–2299.
15. McClure JT, Miller J, DeLuca JL. Comparison of twoELISA screening tests and a non-commercial glutaraldehydecoagulation screening test for the detection of failure of pas-sive transfer in neonatal foals, in Proceedings. 49th AnnualAmerican Association of Equine Practitioners Convention2003;301–305.
16. Pusterla N, Pusterla JB, Spier SJ, et al. Evaluation of theSNAP foal IgG test for the semiquantitative measurement ofimmunoglobulin G in foals. Vet Rec 2002;151:258–260.
17. Etzel LR, Strohbehn RE, McVicker JK. Development of anautomated turbidimetric immunoassay for quantification ofbovine serum immunoglobulin G. Am J Vet Res 1997;58:1201–1205.
18. McCue PM. Evaluation of a turbidimetric immunoassay formeasurement of plasma IgG concentration in foals. Am JVet Res 2007;68:1005–1009.
