Failure of Passive Transfer of Immunity

Passive Transfer of Immunity in Foals:
Assesment and Treatment of Failure of Passive Transfer

  by Robert N. Oglesby DVM

Introduction

Foals must have adequate amounts of good quality first milk, called colostrum, within 12 hours of birth to remain healthy. Unlike most newborns, foals are born without any antibodies (immunoglobulins) to fight infection. He gets these first antibodies from the colostrum and we call this process of the mare transferring antibodies to the foal, passive transfer. Though debate about what constitutes adequate levels of antibodies in the newborn after passive transrer, one thing is certain, without some passive transfer the foal will develop infections and die. This article discusses colostrum and passive transfer in greater detail, testing for passive transfer, and treatment for it. See also Feeding Orphan Foals.

Mechanisms of Passive Transfer

This concept of passive transfer is a bit foreign to many mare owners because the horse is the only specie they may have come into contact with where this is so important. Unlike most species, antibodies are not transferred from the mother to the baby while in the uterus. This is not the same as the baby is unable to make antibodies but when born he has not been exposed to any diseases so does not made any antibodies to them. Following exposure he can make them but by the time he does it will be too late and he will have succumbed to the disease. To tide the neonate over until he makes a set of antibodies to the pathogens in his environment he needs his dam”s antibodies to help ward off infection.

Several events and conditions have to occur for successful transfer. First the mare has to produce good quality colostrum with antibodies to the infectious organisms the foal is likely to encounter. Then the foal must consume the colostrum shortly after birth. The immunoglobulins are large protein molecules that would normally be digested to simple molecules. But for the first 12 hours following birth the foals digestive system is modified so as not to digest the antibodies and has large, at least on a molecular basis, holes in it so the antibodies can be absorbed and transferred to the blood system . These special conditions rapidly change following birth so there is a small window, less than 18 hours where this process can occur. Recently there has been a switch in emphasis on research into the the cause of the high incidence of neonatal septicemia in foals. While previously the umbilical cord was frequently implicated as the source of the infection it is now thought that perhaps this special condition of the neonates bowel may actually be the entry point for most of these infections.

Risk Factors for Passive Transfer Failure

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There are gestational and birth conditions which are associated with a higher incidence of failure of passive transfer but any marked deviation from a normal health last month of preganancy or in the behavior or health of the newborn foal should be considered a reason to suspect possible failure. So you should first be acquainted with the normal events of pregnancy, lactation, birth, and the first 24 hours of the neonates life, ...more. Specific early alerts to possible trouble with colostrum would be:
  • A history of poor nutrition or management of the mare.
  • Mare in thin or worse condition.
  • Grazing fescue pastures after day 300 of pregnancy.
  • Premature birth (less than 325 days) or a premature looking foal.
  • Milk leaking out before birth.
  • A small bag with thin watery fluid at birth
  • Foals slow to stand or that have trouble nursing within 2 hours of birth
  • The mare rejects the foal.

Assessing Colostrum Quality

Though the accuracy of visual assessment has not been judged you can get an idea of at least whether the mare is lactating and though if normal not a guarantee of succssful transfer it abnormal should be viewed with suspicion. You may find milking a mare difficult but it should be attempted with freshly washed hands. Many mares resent having their teats handled so this alone is not a dependable sign of problems and be careful not to get kicked or bit. Good quality colostrum varies considerably in color and consistency, from a clear, thick, yellow fluid to white milk similar to cows milk. There are several laboratory tests that can be performed to check the colostrum or foals immune status. The simplest test on the colostrum is to check its specific gravity with a hydrometer. A reading over 1.060 shows good antibody content.

There is a lot of variation in the above description so alone should not be considered a absolute sign of trouble, instead a sign that further investigation warranted. Lack of development of the bag or watery thin colostrum should be viewed with great suspicion but even good looking colostrum may occasionally be poor in antibody protection, for more information. Early or premature heavy bagging up is often a sign of twins, endometritis, or impending abortion and should cause further investigation, for more information.

Assessing the Foal

The most common reasons for failure of passiver transfer in not related to problems with the mare or quality of the colostrum but because of problems with the foal. Poor nursing because of weakness or inadequate absorption of the antibodies from the intestines because of poorly understood factors can result in failure of passive transfer. The most immediate nee the foal has is energy and the mare's milk is the best source. Without adequate energy intake foals will visibly weaken due to lack of energy in less than 12 hours. If the nutrient content is adequate, but the antibody level deficient or absortion poor foals usually begin getting infections in three to 14 days. Just as it is important to assess the mare and the colostrum it is important that you familiarize yourself with what is normal and you evaluate the foal for any signs of abnormal behavior ...more.

Measuring Transfer

Perhaps the first question is, "should every foal be checked?" In answering this question it is important to remember that once a foal develops a systemic infection they are very difficult and very expensive to treat. These tend to be mixed, resistant, toxin producing, blood infections.

More Information on

Presented at the 2006 Am Ass of Eq Pract:

Evaluation of Five Assays for the Diagnosis of Failure of Passive Transfer of Immunity in Foals

by Rachel Davis and Steeve Gigue` re, DVM, PhD, Diplomate ACVIM

IgG concentration in serum was assessed using zinc sulfate turbidity (Equi Z), glutaraldehyde coagulation (Gammacheck E), semiquantitative immunoassays (Midland 4 Quick Test Kit, Midland 8 Quick Test Kits the Idexx Snap test),and a quantitative immunoassay (DVM Stat). Two single radial immunodiffusion (RID) assays were used as reference methods..

Sensitivity:

Except the Midland 8 test all were considered sensitive enough for screening blood. A finding of adequate transfer meant that the foal was OK with a high degree of confidence. The Midland 8 test would identify some foals as adequate which had lower levels of antibodies. Specificity:

A finding of inadequate transfer was not accurate enough on all the tests except Snap test and the Midland 8 test to base treatment on in all conditions. The other tests would often identify foals as having inadequate transfer that really were OK.

In conclusion it seems like you should be using only the Snap test to screen and base treatment upon.
On the other hand a mare and foal with a picture perfect foaling and no indication of problems is unlikely to develop septic infections, let's peg the incidence somewhere less than 5% for the population with no risk factors. If the problem of failure of passive transfer is caught in the first 24 hours before infection develops it can be corrected with a transfusion. You must decide if spending the extra 50 to 100 dollars for the test is worthwhile. One way to answer this is to ask yourself, "Would I spend 500 to a 1000 dollars on treating a sick foal with a fair to guarded prognosis?" If so the test makes good economic sense. Imporatant: anytime there are risk factors present the chance of failure and subsequent infection goes up so it would be strongly recommend you test, as long as the cost of the transfusion is within your budget.

What constitutes adequate immune transfer is not clear cut. We measure transfer by checking the immunoglobulin concentration of the foal?s blood 18 to 24 hours following birth. There are a number of field test kits to measure this but you have to be careful as the accuracy of the tests vary, see insert on left. Results are usually expressed in milligrams per deciliter (mg/dl). Concentrations below 400 mg/dl are considered failure of passive transfer while above 800 mg/dl is considered a good transfer. In between is considered to partial failure. However there are surveys that have found foals below 400 that remained healthy and problem free while those above 800 develop infections so the results should be interpreted in light of other factors. Concentrations around 400 may be considered adequate if all other conditions and physical findings are good. This includes a healthy mare, a healthy foal, normal placenta and a clean nonstressful environment. On the other hand concentrations under 800 should be considered inadequate if there are signs of stress or illness in the foal. To summarize:
  • 0 - 400 mg/dl = Failure of Passive Transfer
  • 400 - 800 mg/dl = Partial Failure of Transfer
  • 800 - Up = Successful Transfer

Treatment

If problems are identified in the first 12 hours oral therapy can be attempted

If you know from the start that the mare has inadequate colostrum, early oral treatment with frozen colostrum is possible. A foal's ability to absorb the antibodies from the milk is time dependent with the first few hours being the best. After 12 hours the foal's ability to absorb the colostrum is severely impaired and gone by 24 hours.

Banking Colostrum

Frozen colostrum from other mares on the farm is the best choice. 250 ml (one cup) of colostrum can be harvested from normal mares, if the IgG is good. The colostrum can be harvested just after birth but before nursing. The easiest way to evaluate the colostrum is with a hydrometer (Equine Colostrometer, Jorgensen Labortories, Loveland, Colorado) and values above 1.060 are suitable for banking. If values are below this level there is concern that banking may deprive the donor mare's foal of an adequate amount of IgG.

In the past it has been recommended that banked colostrum be obtained after the foal has nursed to ensure the foals health. But in the case of a deficient mare this practice still deprives the foal. Veterinarians at the Uni. of Fla. looked closely at his question and found the recommended regimen above both, protected the newborn, while insuring the quality of the banked colostrum. The collected colostrum can be kept frozen for up to one year. An average foal will require two liters of colostrum divided into four feedings given an hour and a half apart. Blood levels of antibodies should be checked next day to insure adequate transfer. Reference: Colostrum Feeding of Foals and Colostrum Banking Ruth E. Massey, DVM; Michelle M. LeBlanc, DVM; and Elisabeth F. Klapstein, BS. Authors' addresses: Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610. From the 1991 Am. Ass. of Eq Pract Proceedings.

Feeding Equine Serum and Bovine Colostrum

If the deficiency is discovered in the first six to 12 hours postpartum and banked equine colostrum is not available either equine serum or bovine colostrum can be substituted. Because equine serum is low in antibodies compared to colostrum three to 4 liters is required. This should be fed in 500 ml portions every one to two hours. In one project foals were fed bovine colostrum at the same rate of 400 ml every two hours for the first 20 hours with good results. Reference: Absorption of bovine colostral immunoglobulins G and M in newborn foals. Authors: Jean-Pierre Lavoie, DMV; Michael S. Spensley, DVM; Bradford P. Smith, DVM; Judy Mihalyi, BS. From: Am J Vet Res Year: 1989 Volume: 50 Number: 9 Page: 1598
Following oral administration it is imperative to check the success of the transfer by checking the antibody levels in the blood 12 hours later. Low levels at this time indicates the need for IV infusion.

IV Infusion of Equine Serum Will be Necessary After 12 Hours has Passed.

If you suspect or find low levels after the first 12 hours of birth IV treatment is warranted. The foals gut will only absorb the antibodies intact for a short period after birth with the maximal absorption occurring in the first six hours. Serum can be collected from donor horses using human transfusion supplies. The donor should be screened for compatibility with other horse blood, but this is rarely possible given the time constraints. Fortunately transfusion reactions are infrequent in horses if you avoid the foal's mare's blood. Geldings would be safest as they will not have had as much chance at exposure to foreign blood types. Three liters is usually enough for an average size foal but you should recheck the foal several hours after transfusion to be sure.

There are commercial frozen equine plasma or serum. The recommendations on the product should be followed as concentration varies from product to product. An average size foal should receive about 10 grams of IgG if he is healthy and twice that if he is ill. Below are some of the products available:
  • Hi Gamm-Equi., Lake Immunogencies Inc, 1-800-648-9990
  • Polymune, Veterinary Dynamics, Inc., 1-800-645-9743
  • Sera Inc., 913 / 541 - 1307

    Fax: 913/541-1712
  • Diagnon Corp., 3 0 1 / 2 5 1 - 0 6 3 3

    Fax: 301/251-1260

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