1a. Objectives (from AD-416):
The long-term objectives of this project are to develop an improved understanding of the genes involved in controlling feed intake and the efficiency of nutrient utilization and to determine how specific dietary nutrients affect the expression of genes (mRNAs) and gene products (peptides and proteins including those with important post-translational modifications) involved in regulating these processes in poultry. Over the next 5 years we will focus on the following two objectives: Objective 1: Identify and determine the role of specific genes and gene products that influence feeding behavior and nutrient metabolism in young growing broilers, turkey poults, and broiler breeders. Sub-objective 1.A. Determine the effects of the transition of newly hatched chicks and turkey poults from a high-fat nutrient source (yolk) to a high-carbohydrate diet on gene expression patterns in key tissues. Sub-objective 1.B. Determine the effects of feed withdrawal and refeeding on patterns of gene expression and gene product levels in young growing broiler chickens and turkey poults and in the replacement phase of broiler breeder production. Sub-objective 1.C. Determine the effects of genetic selection of chickens for high (HWS) and low (LWS) body weight phenotypes on the expression of genes and gene products that regulate feed intake and metabolic pathway activity. Objective 2: Determine the effects of varying levels of specific dietary nutrients (e.g., protein/amino acids and carbohydrate) and metabolic hormones on the expression of key genes and physiological mechanisms that regulate feed intake and nutrient utilization in young growing broilers and turkey poults. Sub-objective 2.A. Determine the effects of different levels of dietary protein, amino acids and carbohydrate on patterns of gene expression and gene product levels during phase feeding of broiler chickens. Sub-objective 2.B. Determine the effects of administration of specific nutrients and metabolic agents/hormones on physiological mechanisms involved in the regulation of feed intake and nutrient utilization in young growing broilers and turkey poults.
1b. Approach (from AD-416):
This project addresses the need to understand regulatory mechanisms of feed intake and nutrient utilization in poultry species through identification and study of individual genes and gene products involved in these complex and economically important production traits. The first objective will investigate genes controlling feed intake and nutrient utilization and to determine how their expression is affected during the critical adaptation to feeding initiation occurring during early post-hatch development of broiler chickens and turkeys. The consequences of feed restriction and refeeding on expression of genes and gene products involved in key control points for feed intake and metabolic activity at different ages and stages of poultry production will be determined. Two genetic lines of chickens, selected for high and low body weight, will be studied to compare and contrast changes in gene and gene product expression and plasma metabolite and metabolic hormone patterns characteristic of these two phenotypes and to determine how such changes may relate to the marked differences in feed intake and metabolism exhibited by both lines. A second objective will determine the effects of feeding broilers varying levels of crude protein, individual amino acids or carbohydrate on the expression of genes and gene products that play important roles in growth and energy balance and to correlate gene expression and endocrine profiles with changes in whole body parameters such a fat accretion, meat yield and skeletal growth in broilers during the different phases of the production cycle. Broiler chickens and turkey poults from hatch to 4 weeks of age will be administered substances known to affect nutrient levels, endocrine profiles, metabolic activity and feed intake to determine relationships between these parameters and peripheral tissue and central nervous system regulatory mechanisms. Expression of candidate genes will be assayed in chicken and turkey tissue samples using reverse transcription polymerase chain reaction assays. Total RNA from broiler liver, hypothalamus, breast muscle and duodenum tissues sampled at hatch (day 0) and on day 7 post-hatch will be subjected to in-depth replicated microarray screening to determine changes in gene expression related to the initiation of feeding. Plasma samples will be analyzed for metabolite/nutrient levels and a series of metabolic hormones. Tissues will be analyzed for enzyme activities, in vitro lipogenic activity, nutrient-sensing transcription factors, and activity of specific kinase pathways. Information on metabolic and endocrine profiles will then be correlated with changes in gene expression with particular emphasis on those genes whose expression is responsive to nutrient and/or hormonal signaling. This functional genomics approach will yield new information about genes encoding important regulatory factors such as hormones, neuropeptides, receptors, transporters, enzymes and transcription factors that together form a complex and interrelated series of neural, endocrine and metabolic pathway networks working in concert to control feed intake and nutrient utilization in poultry.
3. Progress Report:
During FY2013, progress was made towards both objectives. For Objective 1, the timing for the gene expression of factors involved in the breakdown of proteins into amino acids and the subsequent transport of amino acids from the intestine to the blood stream and vice versa was examined during chicken embryo development. Prior to day 15, only amino acid transporters that move amino acids between intestinal cells and the embryonic blood supply were expressed. This suggests that during early embryo development, the primary movement of amino acids is from the blood to intestine for the growth of the intestinal tract. By day 15, genes for amino acid transporters that take up nutrients from dietary components were detected. This suggests that the embryonic gut is ready to process and absorb amino acids approximately 6 days before hatch. While different regions of the gut have distinct nutrient uptake efficiencies, the expression of amino acid transporters did not differ between the unique functional regions of the embryonic gut. This included a region at the beginning of the large intestine called the cecum, which is not thought to play a role in amino acid absorption; results from this study are the first to suggest otherwise. Throughout embryonic development, high levels of amino acid transporter expression were seen in the liver, which in the embryo carries out most metabolic functions. Additional experiments are ongoing to determine the expression of the amino acid transporters in the gut of chickens collected at hatch and subsequent to feeding through post-hatch day 21. During this time the chicks adjust from the yolk’s high fat diet to a corn/soybean meal diet high in protein and carbohydrates. Progress has also been made toward Objective 2 to determine how the bacteria in the gut is established under normal rearing conditions. Contents of the gut as well as scrapings of the gut lining have been collected from newly hatched broiler chicks up to 21 day old birds. Microbial DNA has been extracted and qualitative/quantitative analysis of the bacterial populations and the population profile variability with age will be examined.
Miska, K.B., Kim, S., Fetterer, R.H., Dalloul, R., Jenkins, M.C. 2013. Macrophage Migration Inhibitory Factor (MIF) of the protozoan parasite Eimeria influences the components of the immune system of its host, the chicken. Parasitology Research. 112:1935-1944.