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Why foals need antibodies

by Rosemary Sharpin

At birth, healthy foals have an immune system, fully developed, ready to protect them from disease-causing bacteria and viruses (pathogens).

When an animal first has contact with a foreign substance, the body prepares a range of protein molecules (called immuno-globulins or antibodies) to attach to any 'invader' or infectious agent and inactivate it.

Immuno-globulins come in five basic forms - IgG, IgA, IgD, IgE and IgM. Each has a different role in protecting the body. Each molecule of immuno-globulin is specific for one particular pathogen or foreign substance. IgG molecules are the predominant type in the blood and colostrum.

As newborn foals have had no contact with pathogens in utero, they have not prepared the basis of this arsenal of IgG antibody 'weapons' the immune system makes when an attack occurs. In short, the body of a newborn foal knows what to do with any 'invader' but has not done this before, so there is no IgG in their blood to fight infection.

From this state, it takes 3-6 weeks to develop strong antibodies to any particular disease-causing agent. In this period any new born is susceptible to infection.

Mother's 'milk' or more especially the first milk the mother makes, which is called colostrum, is needed by the foal to overcome this and to protect it from infections.

Colostrum is a rich mixture of essential nutrients. Vitamins, sugars and a range of important proteins, including a high concentration of antibodies (IgG) to infectious bacteria and viruses that the mother has been exposed to in her environment during pregnancy, which therefore may be an immediate problem for the foal.

So, the sooner a foal takes colostrum from its mother, the sooner it has immediate protection from any disease-causing organisms. This transfer of IgG from the mother to the newborn is called 'passive transfer' of immunity. Foals must receive the IgG in the first 6-12 hours of birth as it is only during this time that the specialised cells in their small intestine are able to absorb the IgG supplied in the colostrum.

Foals not suckling early will have low levels of IgG in their blood, called 'failure of passive transfer' (FPT). As a result, they are more likely to suffer from infections of the gut and lungs and also septic arthritis which may be life threatening .

This tendency to suffer life-threatening illness following FPT (failure to colostrum/IgG from the mother) means insurers will not accept the risk. Cover for 'All Risks of Mortality' will only be issued for the foal if a blood sample is taken and the level of IgG in the foal serum is shown to be 800mg/dl or more.

Even if a foal suckles, it may not get adequate levels of IgG. This can occur if the mare does not make milk or colostrum of any kind, lactates prior to the birth leaking colostrum to waste, or the colostrum does not have enough antibody in it.

Whether or not you wish to insure the foal, monitoring the blood level of IgG, particularly in the first 24 hours of a foal's life, can inform you if the foal is at risk and may enable treatment to be given before foal health is compromised.

Horse Concentration of IgG
Mare Plasma More than 1250mg/dl
Horse Colostrum (first milk) 4000-6000mg/dl depending on breed
New-born Foal Plasma 0mg/dl
Foal Plasma, after adequate suckling in first 3-6 hours after birth More than 800mg/dl