Dynamic changes in protein concentrations of keratins in crop milk and related gene expression in pigeon crops during different incubation and chick rearing stages.

1. The objective of this study was to examine the keratin composition of crop milk, the variation of epithelial thickness and keratin () gene expression in samples from young pigeon during incubation and chick rearing.2. Crop milk was collected from 1-, 3- and 5-day-old squab crops for keratin content analysis. Results showed that accounted for the highest proportion of all detected keratins.3. In total, 42 pairs of adult pigeons were allocated to seven groups according to different stages to collect crop samples. Gene expression studies showed that the gene expression was maximised at rearing Day 15 (15) and R1 in males and females, respectively. gene level was the greatest at R15 in females, whereas it peaked at incubation Day 4 (I4) in males. The and gene levels were inhibited at the peak period of crop milk formation in comparison with I4. In females, expression peaked at I10, whereas it was the greatest at R25 in males. and gene expression was the highest at I10 in females, while and were minimised at I17 and R7 in males, respectively. Gene expressions of and in males and in females were maximised at R1. The and gene levels in females peaked at R7. and expressions in males and females reached a maximum value at R25 and I17, respectively.4. The epithelial thickness of male and female crops reached their greatest levels at R1 and had the highest correlation with .5. These results emphasised the importance of keratinisation in crop milk formation, and different keratins probably play various roles during this period. The K19 was probably a marker for pigeon crop epithelium development. The sex of the parent pigeon affected keratin gene expression profiles.