SAEVA Proceedings 2016 | Page 199

  leucopaenia in older foals is a sign of severe illness. Leucocytosis is associated with infection (older foals), stress or exogenous steroids. Lymphopaenia (<1x109/l) at birth can be associated with EHV (and EAV), prematurity and sepsis. Thrombocytes – similar to adult levels. Thrombocytopaenia can be associated with immune-mediated disease – anti-platelet antibodies via colostrum or drug related. Biochemistry Proteins -Immunoglobulin G (IgG) As there is no transplacental transfer of IgG before birth, foals are born essentially agammaglobulinaemic. During the last few months of gestation, mares concentrate IgG, IgG(T), IgA and IgM in their colostrum. It is these essential immunoglobulins that will confer immunity until the foals own immune 
system is mature. The colostrum also contains complement and lactoferrin, proteins essential for immune function. Specialist enterocytes absorb the immunoglobulins by pinocytosis. These cells have a lifespan of a maximum of twenty-four hours. Maximum absorption occurs within eight hours of life. To obtain adequate transfer of immunity, the foal must ingest around 1 litre of good quality colostrum within the first six hours of life. Maternal IgG has a half-life of 20-23 days. Serum IgG concentrationsa are at their lowest at 1-2 months of age. Foals’ intestines are capable of absorbing IgG for their first 12 hours of life. Providing the mare makes colostrum of good quality in terms of IgG concentration, she does not ‘run milk’ before foaling and the foal sucks sufficient colostrum within the first 12 hours, the foal acquires good circulating IgG levels and therefore adequate passive immunity. In the author’s opinion, foals should have their serum IgG levels checked as a routine preventive medicine policy. Serum samples collected from foals after 12 hours of age should have IgG levels of more than 4g/l and ideally more than 8g/l. Levels of less than 4g/l indicate failure of transfer of colostral immunity and levels of 4-8 g/l indicate partial failure. Foals with levels below 4g/l are considered at risk for neonatal infections and should ideally be transfused with commercial hypermmune plasma and their serum IgG levels re-checked 24 hours later to make sure that IgG levels have risen to acceptable levels. None of the currently available ‘stable-side’ foal serum IgG tests are reliably accurate at the 0-4g/l end of the scale and they are all affected by the presence of inflammatory proteins, especially fibrinogen. IgG can be measured in colostrum immediately after parturition semiquantitatively, using a refractometer. If readings suggest an IgG level of less than 45 g/l, the foal should be considered for donor colostrum 15-­‐18  February  2016      East  London  Convention  Centre,  East  London,  South  Africa     198