|QU, YANG - US Department Of Agriculture (USDA)|
Submitted to: British Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2021
Publication Date: 1/10/2022
Citation: Miska, K.B., Schreier, L.L., Kahl, S., Russell, B.A., Qu, Y., Proszkowiec-Wegla, M.K. 2022. Expression of genes associated with nutrient uptake in intestines of chickens with different growth potentials show temporal changes but are not correlated with growth. British Poultry Science. 63(2):179-193. https://doi.org/10.1080/00071668.2021.1966753.
Interpretive Summary: In the past 60 years the growth of broiler chickens which are used for meat production has been artificially selected by poultry producers. This has resulted in birds which grow very quickly and achieve market weight in less than two months. During the 1950s a typical chicken was used for both egg production and meat, grew slowly, and was much smaller at market weight. The popularity of slow growing meat chickens is increasing with the consumer because there is a growing perception that slow growing chickens are healthier and produce better tasting meat. The purpose of our study was to compare growth parameters in six breeds of chickens that have different growth characteristics and determine whether the molecules in the gut that are responsible for moving nutrients into and out of the intestines are present in different amounts. Three lines of fast growing chickens, two of medium growth, and one of slow growth were used in this study. Chickens were sampled at several time points between embryonic day 19 (before hatch) and day 35 after hatch. The growth parameters showed that all six breeds of chickens grew as expected. The molecular data gathered from this study implied that the expression of the molecules that are responsible for import and export of nutrients in the intestines does not correlate with growth patterns. However, we observed that molecules which import nutrients into the intestine increase for the first two weeks of life followed by a plateau. On the other hand, most of the molecules which function in exporting nutrients out of the intestine and into the blood stream tended to decrease over first two weeks followed by a plateau. The large intestine of the chicken called the ceca also expressed these molecules but in much smaller fashion, since the bulk of nutrient transport take place in the small intestine. The data gathered in this study suggests that patterns of expression of molecules which function in transport of nutrients is hard wired in chickens when comparing birds with very large differences in growth patterns.
Technical Abstract: Over the last 60 years broiler chickens have been selected for rapid growth while maintaining a low feed conversion ratio (FCR). Today’s broilers can attain FCR of approximately 1.5 while undergoing rapid weight gain, making them more efficient. This study was designed to compare expression of genes that encode proteins located at either the brush border (BB) or basolateral (BL) surface of the gut epithelium among fast and slow growing broiler strains. Gene expression changes between fast and slow growing broilers may reflect differences in uptake of nutrients. Six strains of chicks with different growth capacities were used: Ross 708, Hubbard H1 (HH1), Cobb500, Longnecker’s Heritage (LHR), Red-Bro, and the Athens Canadian Randombred Control (ACRBC). Fertile eggs were hatched, and birds were raised in floor pens and sampled at embryonic day 19, day of hatch, and days (d) 7, 14, 21, 28 and 35 post-hatch (PH). At each sampling a portion of the duodenum, jejunum, ileum, and ceca were snap frozen for RNA isolation. Performance parameters indicated that Ross 708, HH1, and Cobb500 had the greatest body weights (BW), reaching 2,172 g, 2,320 g, and 2137 g, respectively, at d35 PH. Red Bro and LHR birds attained BWs of 1,308 g and 1,436 g, while ACRBCs weighed only 421 g at d35 PH. Quantitative RT-PCR was performed on 13 genes which encode proteins associated with nutrient processing and uptake. Analysis was carried out using SigmaPlot 14 (ANOVA) of eight genes which encode proteins associated with the BB of the gut epithelium, including: Aminopeptidase N (APN), four amino acid transporters, (ATBo,+, BoAT, bo,+AT, EAAT3) a di- and tri- peptide transporter (PepT1), and two sugar transporters (GLUT5 and SGLT1). Additionally, analysis of five genes which encode proteins associated with the BL gut epithelium: four amino acid transporters (CAT1, CAT2, LAT1, and '+LAT1), and a single sugar transporter (GLUT2) was carried out. The results indicate that while strain specific differences in gene expression were noted they did not associate with growth rate. In most cases, genes encoding BB associated proteins increased in expression over time (P < 0.05) in the duodenum, jejunum, and ileum, while in the ceca the expression decreased. On the other hand, mRNA BL associated proteins decreased (P < 0.05) in expression over time in all gut segments with exception of GLUT2 which increased in expression in the small intestine. The temporal changes in gene expression were very consistent among bird strains. In conclusion, temporal and strain differences in gene expression were noted, however, differences may not be associated with growth efficiency.