2009 Annual Report
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.
Progress has been made during the past year and work continues in the following areas:.
1)Evaluating the use of distillers dried grains, a byproduct of ethanol production from corn, in formulating diets fed to broiler chickens and determining the potential adaptability of commercial broilers developed for use in the United States to lower energy feeds containing less corn;.
2)Application of global (whole genome) and individual gene expression analysis to study the genetic basis for important metabolic adaptations occurring in response to the initiation of feeding during the first week after hatching, a crucial period of growth and development for broiler chickens;.
3)Understanding the impact of different feeding practices on expression of genes that regulate lipid synthesis in the liver of female broiler breeder chickens and the consequences for body fat accumulation and obesity-related health issues during production; and.
4)Investigating genetic mechanisms linking nutrient and energy sensing with the control of metabolic activity to maintain energy balance in poultry, particularly as they relate to lipid synthesis and fat accretion in broiler chickens. The progress made in each of these areas contributes to understanding the mechanisms that regulate feed intake and nutrient utilization in poultry during different phases of the production cycle.
Fat metabolism is activated in broiler chickens immediately after hatching. The first week post-hatch is a crucial period of growth and development for broiler chickens. How well the broiler chick transitions from utilizing nutrients provided from the egg contents (especially high fat yolk) to those provided from a high carbohydrate low fat feed consumed shortly after hatching determines not only its survival, but also its subsequent performance during the remainder of the production cycle. Since fat is an important energy source, it is vital that the newly hatched chick quickly develop the ability to regulate the production, utilization and storage of the requisite amount of fat required for optimal growth and development. Therefore, the goal of this work was to relate changes in the functioning of individual genes and gene networks with the metabolic adaptations that occur in response to initiation of feed consumption right after hatch in broiler chickens. To do this we utilized global gene expression analysis encompassing the entire chicken genome to evaluate unique gene functions in liver, a key organ involved in regulating fat metabolism in the chicken. Our analysis revealed that a variety of genes involved in fatty acid, cholesterol and carbohydrate metabolism were coordinately activated with the onset of feed consumption during the first week after hatching. Some of these genes had been previously identified and studied while others were found to be new candidates for further study. The results from this work will help define genetic mechanisms that regulate the post-hatch metabolic transition in broiler chicks and suggest possible nutritional and management approaches to optimize broiler performance during this critical time of production.
Management of female broiler breeder candidates. Broiler breeders are feed restricted to reduce the occurrence of reproductive problems associated with obesity. Skip-a-day feed restriction programs are commonly used in preference to everyday programs even though there is a potential for excess fat accumulation by using the skip-a-day regimen. A project was undertaken to determine the effects of certain feed management regimens on metabolism of the broiler breeder candidate. The regimens were.
Use of distillers dried grains by the modern broiler chicken. Ethanol production may exacerbate limited availability of corn normally used for broiler production. In addition, a by product of ethanol fermentation from corn yields a feed grade product (distillers dried grains with solubles, DDGS) of unknown nutritional quality. Formulating diets with DDGS results in lower energy feeds that may be inappropriate for American broilers which have been selected based on growth attained with much higher energy diets. We hypothesized that diets formulated with DDGS in appropriate proportions may cause birds to perform differently from those fed traditional diets formulated from a corn-soybean meal base. Birds were fed diets containing graded levels of crude protein in base diets formulated with DDGS or corn and soybean meal. Lipid metabolism was influenced by dietary DDGS, although there appeared to be an adaptation period prior to reaching final metabolic equilibrium. Thus, American broilers, like their European counterparts, are somewhat tolerant of deviations from the normal corn-soybean diets. Despite previous data that have shown that selection practices in the U.S. involving the use of simplified corn soybean meal diets resulted in birds that do not tolerate a wide range of dietary ingredients, this work clearly demonstrated that the modern broiler can tolerate and thrive on diets containing quantities of DDGS that were previously thought to inhibit growth. However, this is contingent on an accurate assessment of nutrient levels supplied by the DDGS used in broiler diet formulations.
1)restricted amount of feed given to birds on a daily basis (every day feeding) and.
2)twice the daily feed allocation but only given every other day (skip-a-day). Skip-a-day feeding increased the expression of certain genes implicated in the regulation of lipid metabolism. An increase in liver lipid content accompanied the increase in gene expression which could be deleterious to the long-term health of the birds. These results demonstrate potentially significant impacts of different feeding regimens, currently in use by poultry producers, on gene expression patterns that affect fat metabolism in breeder chickens.
Nutrient and energy sensing mechanisms regulate fat in the broiler chicken. Poultry producers face numerous challenges related to the regulation of energy balance in commercial lines of birds that have been intensively selected for rapid growth rate and enhanced meat yield. For example, modern broiler chickens do not adequately regulate energy intake and metabolic activity to achieve energy balance leading to excessive weight gain and fat accumulation characteristic of obesity. The objective of this study was to identify and characterize the relationship between nutrient and energy-sensing mechanisms and the regulation of fat synthesis in liver. We investigated changes in the expression and activities of different genes that encode.
1)an energy sensing enzyme that regulates metabolic activity,.
2)a nutrient (glucose)-responsive transcription factor that regulates gene function and.
3)metabolic enzymes involved in lipid synthesis in broiler chickens during altered energy states caused by fasting and refeeding at 3-weeks of age as well as in developing embryos and newly hatched chicks undergoing the transition from egg-based nutrition to post-hatch feeding. Our results identified and characterized the genetic basis governing energetic efficiency (i.e., balance of intake vs. usage) and determined potential regulatory mechanisms for fat accumulation in broiler chickens that function at different stages of the production cycle.
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Proszkowiec Weglarz, M., Richards, M.P. 2009. Expression and activity of the 5'-adenosine monophosphate-activated protein kinase pathway in selected tissues during chicken embryonic development. Poultry Science. 88(1):159-178.
Proszkowiec-Weglarz, M., Richards, M.P., Humphrey, B., Rosebrough, R.W., McMurtry, J.P. 2009. AMP-activated protein kinase and carbohydrate response element binding protein: A study of two potential regulatory factors in the hepatic lipogenic program of broiler chickens. Journal of Comparative Biochemistry and Physiology. 154(1):68-79.
Richards, M.P., McMurtry, J.P. 2009. The avian proglucagon system. General and Comparative Endocrinology. 163(1/2):39-46.
Rosebrough, R.W., Russell, B.A., Richards, M.P. 2009. Effects of Short Term Triiodothyronine administration to broiler chickens fed methimazole. Comparative Biochemistry and Physiology. 150:72-78.
Sethi, P.K., McMurtry, J.P., Pesti, G.M., Aggrey, S.E. 2008. Physiological responses to divergent selection for phytate phosphorus bioavailability in a randombred chicken population. Poultry Science. 87:2512-2516
Shiraishi, J., Yanagita, K., Nishikawa, F., Tahara, Y., Fujita, M., McMurtry, J.P., Bungo, T. A . 2009. Comparison of the Anorexic Effects of Chicken, Porcine, Human and Bovine Insulin on the Central Nervous System of Chicks. Journal of Poultry Science. 46:144-148.