Clinical aspects of passive immunity in foals.

The research article discusses the passive immunity in foals, focusing on how it is obtained, how it functions, and when foals develop the competency to actively produce their own immunity cells.

Transfer of Passive Immunity

• The article first discusses how passive immunity is transferred from a mare (mother horse) to a foal. This process includes the creation of colostrum, which are immune proteins, by the mare in late gestation that are then fed to the foal shortly after birth.
• A healthy mare will have a period of colostrum secretion that is short-lived and levels that drop off after 24 hours. The article highlights early onset lactation in mares as a common problem that reduces the effectiveness of the transferred immunity.

Absorption of Colostral Proteins

• The paper then goes on to explain the absorption process that happens when the foal ingests the colostrum. Special cells in the foal’s small intestine pick up these proteins and move them into the systemic bloodstream.
• This mechanism is highly effective just after birth, but it loses its efficiency quickly and stops entirely within 24 hours. The same absorption process also picks up other proteins in the milk, but these do not serve immunological purposes and are quickly excreted.

Immune Development in Foals

• In healthy foals, the window of susceptibility to infections narrows rapidly due to the quick acquisition of the passive immunity. Foals attain adult horse levels of specific antibodies within 12-18 hours of birth.
• However, the passive immunity only lasts for up to six months, and for a period before its expiration, the antibody level may not be sufficiently protective.
• A foal begins developing active immunity at around two weeks of age, but it is a slow process. Only by the end of the first month do their antibody levels start to reach protective amounts, which then continue to rise over the next few months, approximately levelling with adult horses by the third month.