Browsing by Subject "Amino acid transporter"

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Characterization of host and bacterial proteins in crossbred grower pigs at marginal lysine concentration
(2025) Kurz, Alina; Seifert, Jana
The current pork production strategies still result in high nitrogen emissions and thus harmful effects on the environment. The animals excrete about two-thirds of the protein in the diet unused, which increases nitrogen emissions and makes feeding the animals according to their needs expensive and inefficient. To minimize the negative aspects of pork production, it is important to reduce the use of proteins in feed while improving the protein efficiency of pigs. Improving protein efficiency requires a comprehensive understanding of physiological processes, particularly enzymatic activities, amino acid transporter capacities, the proteome, the metabolome and the microbiome. The aim of this work was therefore to identify animal- specific and quantitatively expressed proteins, enzymes, amino acid transporters and metabolites and to correlate these findings with protein turnover data. The study also examined whether the efficiency of protein utilization is influenced by these variables. A total of 48 male crossbred animals (German Landrace x Pietrain) were slaughtered in the 21st week of life for the present experiment. The animals were kept individually under the same conditions from the 75th day of life until the day of slaughter. A two-phase ad libitum feeding was carried out, with the change from phase 1 to phase 2 taking place in the 14th week of life. Since the genetic potential of protein utilization efficiency was to be estimated, the content of the first limiting amino acid lysine was 90 %, just below the GfE (2006) requirement limit in order to ensure a limiting factor for the protein approach. Thus, lysine was the limiting factor for protein retention and allowed animals to exploit their full genetic potential for protein utilization. After euthanizing, the animals were opened, and the stomach, small intestine and large intestine removed. Mucosal samples were taken from the sections of the pars nonglandularis, cardiac gland zone and pars pylorica, as well as digesta samples from the stomach. In addition, digesta and mucosal samples were collected from the duodenum, jejunum, ileum, colon, and cecum. The proteome in all samples was analyzed. The metabolome and enzyme activities were determined in all digesta samples. In addition, amino acid transporter expression was examined in all small intestinal mucosal samples. The activity of the enzymes trypsin, chymotrypsin, carboxypeptidase A and carboxypeptidase B were examined in the digesta samples from all sections. The highest activities were found in the small intestine, the lowest activities in the stomach and large intestine. The trypsin and chymotrypsin activity was highest in the jejunum, whereas the activities of the carboxypeptidases were highest in the duodenum. In addition, individual animal differences in enzyme activities could be identified. In addition, the expression rate of various amino acid transporters was examined in the present work. In the duodenum the transporter SLC1A5 showed the highest expression rate, in the jejunum the transporters SLC5A1 and SLC6A19. In the ileum, the rates of the transporters SLC1A1, SLC7A1 and SLC7A9 were at the highest level. The identification of the host proteome revealed different protein patterns in the examined sections of the gastrointestinal tract. In particular, host proteins were identified in the mucosa samples, with the exception of those from the ileum and cecum. The high number of host proteins in the mucosa samples, which are associated with cellular processes and metabolism, underlines its role in physiological digestive processes. In addition, the examined host proteins could be assigned to numerous KEGG pathways, thus creating a deeper understanding of physiological and metabolic pathways. The study of the bacterial proteome allowed not only categorization into different metabolic pathways, but also identification of the active microbiome in the different sections. For example, it was shown that Firmicutes dominate in the stomach and small intestine, whereas Bacteroidetes are mainly found in the large intestine. This highlights the different roles of the sections examined, with Firmicutes being primarily responsible for breaking down proteins and carbohydrates and Bacteroidetes playing a central role in the fermentation of undigested proteins and carbohydrates in the large intestine. Additionally, the increased presence of Tenericutes in the mucosal samples indicated a possible specialization of this family to the conditions in the mucosal environment, where they interact with host cells and contribute to metabolic processes. The identification of numerous unclassified bacterial groups also shows how complex the composition of the microbiome is and that further research must be carried out in order to be able to fully identify connections. The examination of the various metabolites in the digesta samples from the gastrointestinal tract showed clear differences in the detection rate. While the fatty acids acetate, butyrate, valerate, isobutyrate and propionate were found primarily in the sections of the large intestine, lactate, isovalerate and the amino acids showed a higher occurrence in the sections of the small intestine. This is in line with the scientific knowledge that fatty acids are primarily formed during microbial fermentation in the large intestine and should therefore occur in higher quantities here. Overall, the results of the present work showed that, in addition to physiological differences between the sections of the gastrointestinal tract, there also appear to be significant animal- specific differences in all parameters examined. These differences can have an influence on the efficiency of the animals, but it is still important to find out which factors cause these differences. Since the feeding, husbandry concept and experimental design were chosen in such a way that there is as little variation and discrepancy between the animals as possible, a genetic influence on the efficiency of the animals cannot be ruled out. If the animals' genetic potential to use nitrogen efficiently becomes apparent, a further foundation stone has been laid for making pork production tailored to needs and conserving resources and the environment.