Liu, Kuan-Ling2021-01-232021-01-232019-08-01vt_gsexam:21745http://hdl.handle.net/10919/102025In the broiler industry, chicks are often deprived of feed and water up to 48 h posthatch. This delayed access to feed (DAF) has been found to inhibit small intestinal development, compromising growth of the chick. To further understand the impact of DAF on small intestines at the molecular level, many developmental genes that regulate intestinal development were investigated. The objective of this study was to determine the effect of DAF on early posthatch broiler small intestinal morphology, which includes villus height (VH) and crypt depth (CD), and to quantify changes in regulatory genes, such as Olfactomedin 4 (Olfm4), Marker of Ki-67 (Ki-67), Peptide Transporter 1 (PepT1), and Mucin 2 (Muc2), in response to DAF. The Olfm4 mRNA can clearly identify stem cells in the intestinal crypt, which allows VH and CD to be measured, while Ki-67 marks the proliferating cells. The peptide transporter PepT1 is located on intestinal epithelial cells and plays a critical role in transporting di- and tripeptides. Muc2, which is secreted from goblet cells, forms mucus that lines the intestinal epithelial cells acting as a layer of protective coating. Cobb 500 chicks, hatching within a 12 h window, were randomly allocated into three experimental groups: control with no feed delay (ND), 24 h feed delay (D24), and 36 h feed delay (D36). Quantification of Olfm4, Ki-67, PepT1, and Muc2 mRNA abundance were investigated by quantitative PCR, in duodenum, jejunum, and ileum at 0 h, 24 h, 36 h, 72 h, 120 h, and 168 h posthatch. Additionally, localization of cells expressing each gene was visualized using in-situ hybridization at all listed times except 168 h posthatch. Statistical analysis was performed using JMP Pro 14, and significant differences between treatments within a collection day were determined by t-test and one-way ANOVA (P < 0.05). In the ND group, duodenal CD at 0 h was greatest compared to all other time points. With DAF, the duodenal VH of D36 chicks was lower at 36 h (P < 0.001) and 72 h (P = 0.002) compared to ND chicks. In the jejunum and ileum, the VH of D36 chicks was lower at 120 h (P = 0.005) and 72 h (P = 0.03), respectively, compared to ND chicks. In contrast, the VH of D24 chicks at 24 h was greater than ND (P = 0.004) in the jejunum. There was no difference between treatments by 168 h in all intestinal segments. The CD was also lower in DAF groups compared to ND but only in the jejunum and ileum. In contrast, duodenal CD was greater in D24 chicks at 24 h (P = 0.039) and in D36 chicks at 36 h (P < 0.0001) compared to ND chicks, but the difference was no longer significant by 72 h. The VH/CD ratio was lower in all three segments, except the ileum displayed a greater VH/CD ratio in D24 and D36 chicks at 24 h and 36 h, respectively, compared to ND chicks. The mRNA abundance of Olfm4 and Ki-67 was greater in DAF groups upon refeeding, but not until 120 h. The PepT1 mRNA abundance was greater in DAF groups while the abundance of Muc2 mRNA was lower. This difference in mRNA abundance level was more prominent in the duodenum and jejunum. From the analysis of number and distribution of goblet cells found in the upper half and lower half of the villi, expressed as a ratio (VU/VL), a greater ratio was observed in delayed groups compared to ND. In summary, while DAF resulted in altered small intestinal morphology with an effect more pronounced in D36 than D24 chicks, upon refeeding, some genes important to intestinal development were upregulated as a response to the treatment.ETDIn Copyrightintestinal morphologyolfactomedin 4Ki-67peptide transporter 1mucin 2Thesis