# Dynamic Changes in the Crop Milk and Salivary Microbiota of Breeding Pigeons During the Raising Brooding Period

## TL;DR

This study tracks changes in the microbiota of pigeon crop milk and saliva during the brooding period, revealing how these microbial communities evolve and may influence squab health.

## Contribution

The study reveals temporal dynamics and functional roles of crop milk and salivary microbiota in pigeons during brooding, offering new insights for poultry health.

## Key findings

- α diversity in crop milk and salivary microbiota increased over time during the brooding period.
- Ligilactobacillus was the most abundant genus in crop milk, while saliva contained more potentially pathogenic bacteria.
- A significant negative correlation was found between Ligilactobacillus in crop milk and Psittacicella in saliva.

## Abstract

As an important poultry species and model bird, pigeons rely on crop milk as the sole source of nutrition for squabs during early development, while saliva plays a crucial role in parental feeding behaviors such as regurgitation. However, the current understanding of the composition, origin, succession patterns, and potential functional roles of the microbial communities in pigeon crop milk and saliva throughout the reproductive cycle (particularly during the brooding period) remains limited. This study tracked the dynamic changes in the microbial communities of crop milk and saliva during the brooding period, revealing their temporal succession patterns. Our findings provide essential baseline data for understanding the potential roles of crop milk microbiota in the colonization of squab gut microbiota, development of the immune system, and nutrient digestion/absorption. Furthermore, these results may offer new insights for poultry health management and probiotic development.

The microbiota within crop milk not only participates in the physiological regulation of parent pigeons but also promotes the healthy growth of squabs. Consequently, microbial sequencing of both crop milk and the saliva through which it passes is essential to elucidate microbial changes in both compartments during the raising brooding period. This study sampled crop milk and saliva of Mimas at three distinct time points corresponding to Days 1, 4, and 7 of raising brooding, and collected samples from three pairs of healthy breeding pigeons with similar body weights at each time point. The results demonstrated that α diversity increased in both the crop milk and salivary microbiota over time, surpassing the levels observed at the initial secretion stage. Compared to R1, the Simpson index of the salivary microbiome was significantly higher at R7 (p < 0.05). Ligilactobacillus constituted the most abundant genus in crop milk, whereas saliva harbored a greater diversity of potentially pathogenic bacteria. Phylogenetic analysis revealed a close evolutionary relationship between Ligilactobacillus and Enterococcus in crop milk, suggesting potential functional synergy. Furthermore, functional prediction indicated that ABC transporter-related genes presented the lowest expression in the crop milk microbiota during its peak secretion period. Notably, Pearson correlation analysis revealed a significant negative correlation between Ligilactobacillus abundance in crop milk and Psittacicella abundance in saliva. In summary, the crop milk and salivary microbiota exhibit distinct temporal dynamics, and their specific microbial compositions and functions can provide new research directions for the healthy breeding of squabs.