ANSC20003 Chap.11 Immunity in the Foetus and the Newborn
Immunity in the Foetus and the Newborn
Built late, and needed immediately
Of the lymphoid organs the thymus arrives first, with the lymphoid organs, and B cells, and the antibody they make, turn up late. The adaptive side is therefore still unfinished at birth and early defence relies mainly on innate mechanisms, which makes passive transfer from the mother a survival requirement rather than an optimisation.
The milestones are species specific and consistently late relative to birth, and early microbial colonisation contributes to the maturation that follows.
The placenta decides how much rests on the first feed
Ruminants, horses and pigs transfer no antibody across the placenta, so colostrum supplies all systemic immunoglobulin.
Dogs and cats receive a small amount of prenatal IgG through a different placental structure and still require colostrum for full immunity. Primates transfer IgG fully before birth. Milk after colostrum is a different thing again: it is not taken up systemically and provides local protection in the intestinal tract, ceasing at weaning.
Colostrum therefore defends the circulation and milk defends the gut.
An absorptive window measured in hours
The newborn gut is only temporarily permeable to whole immunoglobulins. IgG is picked up by a receptor on the intestinal cells and ferried across whole into the circulation, and absorption is highest immediately after birth before dropping sharply within the first day.
Feeding colostrum speeds closure while delay extends it slightly.
Peak serum antibody is reached within about the first day and then declines over weeks, and maternal antibody influences immune development as well as providing immediate protection.
Three failure modes and one clock
Passive transfer fails through production, when the dam's colostrum is poor or insufficient; ingestion, when the newborn does not drink enough; or absorption, when the gut does not take up what was drunk.
Evaluation is timed for after absorption is complete, and several assays are available with different speed and accuracy trade-offs. Management follows the clock: oral colostrum works only within the first hours, and after that an intravenous route is required. Maternal antibody also blocks early vaccination, which is why schedules use several doses rather than one well-timed one.
What this chapter covers
- 01
Why adaptive immunity is immature at birth and what covers the gap
- 02
Species differences in prenatal transfer, and what each group depends on
- 03
Colostrum against milk, and the two compartments they defend
- 04
Receptor-mediated absorption of intact immunoglobulin, and gut closure
- 05
Production, ingestion and absorption failure, and where each is common
- 06
Timing the test for after absorption is complete, and the assays available
- 07
Maternal antibody interference with vaccination, and how schedules work around it
Choosing the route for a foal with low immunoglobulin at twenty hours
- 1Explain what the timing of the measurement means.
- 1Name the intervention and why it bypasses the problem.
- 1State the follow-up step and why it matters.
Key terms
- Colostrum
- The first mammary secretion after birth, rich in immunoglobulin, cytokines and live immune cells.
- Gut closure
- The loss of the newborn intestine's ability to absorb whole immunoglobulins, occurring within the first day of life.
- Lactogenic immunity
- Protection from antibody in milk, which is not absorbed systemically and acts locally in the intestinal tract.
- Failure of passive transfer
- A shortfall in maternally derived immunoglobulin in a newborn, arising from production, ingestion or absorption failure.
- Maternal antibody interference
- The suppression of a neonate's own antibody synthesis by antibody received from its dam, which blocks early vaccination.
Immunity in the Foetus and the Newborn FAQ
Why is colostrum more urgent for a calf than for a puppy?
Cattle transfer no antibody across the placenta, so a calf's entire systemic immunoglobulin comes from colostrum. Dogs receive a small amount of IgG before birth through a different placental structure, so a puppy is not born defenceless. The lecture is still explicit that colostrum remains essential for full immunity in dogs and cats.
What is the difference between colostrum and milk for a newborn?
Colostrum supplies immunoglobulin that is absorbed into the circulation and defends against systemic infection. Antibody in milk is not taken up systemically; it provides local protection in the intestinal tract against enteric pathogens and stops at weaning. They defend different compartments.
How do you decide which of the three failure modes has occurred?
By the history rather than by the value. Poor or insufficient colostrum from the dam points to production failure, a newborn that did not drink enough points to ingestion failure, and a newborn that drank adequately but has low serum immunoglobulin points to absorption failure. The last is common in foals even under good management.
Why is a newborn not simply vaccinated instead?
Maternal antibody from colostrum inhibits the neonate's own antibody synthesis, so a vaccine given while it is high does not take. Because the level at which blocking stops varies between individuals, the practical answer is a series of doses across a range of ages rather than one dose at a predicted time.
Exam move
Learn the species table cold, because almost every clinical decision in this chapter is a lookup into it, and practise running it backwards from a clinical problem to the row. Keep the timings exact: the absorptive window, when the evaluation is done, and when the oral route stops working, since all three appear in scenario questions.
For the three failure modes, rehearse assigning one from a short history, and be ready to name the intervention that matches the animal's age rather than the severity of the deficit.
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