Immunity Mod 3—Development in the Fetus and Newborn

Read Chapter 21: Neonatal Care of Puppy, Kitten, and Foal from the textbook.

Definition: Tolerance refers to the immune system's ability to manage self-antigens.
Importance: Prevents autoimmune responses by distinguishing between self and non-self.
Mechanism: The immune system learns tolerance by destroying or suppressing B and T lymphocytes with receptors that recognize self-epitopes.
Crucial period: Exposure to antigens before birth enhances tolerance.
Example: Calf chimeras—mixing blood or embryonic cells in utero leads to tolerance to each other's antigens, as they accept the transfusion without an immune response.

Immune systems of domestic animals are well-developed pre-birth.
Susceptibility to infections is due to the unprimed immune response rather than an inability to respond.
Every microbial invasion requires a primary immune response due to the lack of memory cells.
Development Pattern:
- The thymus is the first lymphoid organ developing, followed by the spleen and lymph nodes.
- Significant antibody levels appear late in fetal life.
- Not all antigens stimulate fetal lymphoid tissue equally.
Most species can respond to immune stimuli by the second trimester.
Maternal infections can lead to birth defects or fetal death, exemplified by bovine viral diarrhea (BVD) infections based on gestational age:
- Days 50–100: Abortion of the fetus.
- Days 100–150: Congenital defects, especially CNS and ocular issues.
- Days 150–190: Immunotolerance to BVD, resulting in persistently infected carriers.
- Post Day 190: Fetus develops immune responses and remains healthy.

Colostrum: The yellow, milky fluid produced by the mammary gland around parturition, rich in immunoglobulins (IgG, IgA, IgE, IgM).

Suckling shortly after birth ensures low proteolytic activity in the digestive tract, allowing proteins to pass intact.
Absorption is maximal right after birth and diminishes significantly after 6 hours; negligible after 24 hours.
Successful Ig absorption raises serum levels to adult-equivalent amounts, providing temporary passive immunity.
Maintains local immunity in the gastrointestinal tract, reducing oral infections and diarrhea in newborns raised on colostrum.

Read Chapter 8: Preventative Health Programs—focus on the section regarding immunity and colostrum.

Read Chapter 20: Large Animal Medical Nursing—focus on neonatal care and diseases.

After birth, newborns encounter foreign antigens and exhibit a primary immunological response characterized by a prolonged lag and low antibody concentration, necessitating immunological support through passive immunity (transfer from mother).
The effectiveness of maternal antibody transfer is critically influenced by placental structure:
- Primates and rodents: Efficient antibody transfer (protection from infections).
- Carnivores: Limited (~5-10% transfer).
- Equine and ruminants: No placental transfer, thus immediate colostrum consumption is essential.

Insufficient Ingestion of Immunoglobulins:
- Low colostrum yield from the mother.
- Low Ig concentration in colostrum (first-time mothers or non-vaccinated dams).
- Poor suckling due to maternal behavior, udder conformation, or trauma to the newborn.
Insufficient Absorption:
- Delayed ingestion (>6 hours postpartum) reduces efficiency.
- Stress factors and neonatal health (pre- or post-mature infants) impact absorption efficacy.

Diagnosis is most reliable 24-48 hours post-birth by measuring immunoglobulin levels in serum:
- Use a refractometer to assess serum total protein: high levels indicate successful transfer.
- Zn sulfate or sodium sulfite turbidity tests.
- Serum electrophoresis identifies protein profiles based on size, charge, and shape.

Ig levels outcomes:
- >400 mg/dl IgG: Good passive transfer.
- 200–400 mg/dl: Monitor and treat at infection onset.
- <200 mg/dl (within 3 weeks): Immediate treatment necessary.
- If <15 hours old, administer oral colostrum (fresh/frozen); if older, use IV plasma infusion.

Ig levels outcomes summarized:
- Total protein >6.0 g/dl corresponds to ~1790 mg/dl IgG: Good.
- Total protein <5.0 g/dl (~890 mg/dl IgG): At risk; consider plasma treatment.

Ensure dams are appropriately vaccinated and nourished.
Select for optimal conformation (including mammary glands).
Minimize stress pre- and post-natal through excellent housing and care practices.
Provide each newborn with 5-10% body weight in colostrum within 6 hours of birth from an immunocompetent source.

Passive antibodies inhibit further antibody production, leading to a refractory period affecting subsequent vaccinations.
Variance in maternal antibody half-life influences immunity:
- For example, half-lives of maternal antibodies against canine distemper (8.4 days) and feline panleukopenia (9.5 days).

Maternal antibodies are transferred to the yolk pre-hatching, and chicks absorb these for 24 hours post-hatching, inhibiting successful vaccination for multiple days.
Monitoring vaccinations and proper husbandry is paramount to prevent diseases such as Gumboro (infectious bursal disease virus).

Passive immunity through maternal antibodies, facilitated by colostrum and placental transfer (where applicable), is crucial for newborn health.
Ensuring proper management before and after birthing helps enhance immunity and survival rates among newborns.
Different species exhibit diverse capabilities for passively acquiring immunity based on placental structure, underscoring the importance of immediate colostrum intake for equine and ruminants.