# Early Deficient Lactation Differentially Affects Neonatal Thymic Cortical Development and Humoral Immune Responses in Rats

## TL;DR

This study shows that poor lactation in rats due to low prolactin harms neonatal thymic development and immune responses.

## Contribution

The study introduces a novel rat model to investigate lactation deficiency's impact on neonatal immune development.

## Key findings

- Early hypoPRL in rats leads to increased pup mortality and reduced body weight and weight gain.
- Thymic development is impaired with reduced thymus weight and altered lymphocyte development.
- Deficient lactation compromises passive immune transfer, reducing OVA-specific immunoglobulin levels in pups.

## Abstract

Hypoprolactinemia (hypoPRL) disrupts lactation and compromises milk production. Although maternal milk is a critical source of nutrients and bioactive compounds for newborns, the consequences of deficient lactation based on reduced milk quantity on the offspring’s immune development remain incompletely understood. Therefore, this study aimed to elucidate how deficient lactation due to hypoPRL interferes with offspring immunity and development. Female Sprague Dawley (SD) and spontaneous hypoPRL Oncins France Colony A (OFA) rats were euthanized on day 2 of lactation to assess the impact of hypoPRL on serum, milk, and tissue samples. We demonstrated that early deficient lactation in the OFA model impaired maternal performance, leading to increased pup mortality during early lactation. OFA pups exhibited reduced body weight and weight gain, decreased cerebral weight and index, and an increased cephalization index. Thymic development was markedly altered, as evidenced by reduced thymus weight, area, and cortical extension. These structural changes were accompanied by increased thymic Rag 1 expression, suggesting altered lymphocyte development. In parallel, passive immune transfer was compromised, with reduced levels of OVA-specific immunoglobulin isotypes detected in pup serum, reflecting changes in milk-derived immune support. In summary, maternal hypoPRL during early lactation adversely affects offspring growth and thymic maturation with lasting consequences for neonatal immune maturation. This study provides a novel experimental framework to investigate the consequences of lactation deficiency with potential implications for understanding lactation insufficiency and its impact on neonatal immune exposure.