Recipient Organization
UNIVERSITY OF ARKANSAS
(N/A)
FAYETTEVILLE,AR 72703
Performing Department
Poultry Sciences
Non Technical Summary
Currently chicken makes up approximately 75 percent of the major domesticated animals in the world, with a 2011 US population of over 19 billion. This domination is clearly linked to the general rise in per capita consumption of poultry during the same time. By 2018, Americans consumed in excess of 109 lb. of poultry per capita; of which >93 lb. were chicken alone (National Chicken Council, 2018). The modern broiler-type chicken attains a 5.5 lb. body weight in 40-42 days of age with an overall feed efficiency of less than 1.8. Approximately 85-90% of this change in growth has been attributed to selection for growth, and has been achieved by reducing the market age to the same body weight by one day per year. With continued progress for further-processed products sector of the industry there has been a shift in market age to slaughter. This has resulted in the re-emergence of physiological and metabolic syndromes. The normal growth process involves the simultaneous deposition of neurological tissue during embryonic development. Post hatch bone, muscle, and fat each exhibit an individual pattern of accumulation. The age at which selection is applied can have a tremendous impact on response (Anthony, 2017). For example, selection at the point of inflection leaves some characters in their juvenile state, while accelerating the growth of the others. For modern selection programs there is a relatively large increase in the proportion of muscle mass in chickens selected for high body weight early post hatch as compared to late selection. Domestication, controlled reproduction and genetic improvement have improved broiler survival, however, producers continue to strive for more. The broiler industry has seen new challenges in the form of obesity, skeletal problems, muscle myopathies, ascites and maladaptation to stress. Reduced reproductive performance has been observed in broiler breeders in the form of erratic ovulation and defective egg syndrome. On the male side, reports suggest the ability of the broiler-breeder to fertilize eggs is declining at a rate of 0.5% per generation. These factors challenge poultry scientists to find temporary and permanent solutions to problems as they arise in an effort to maintain animal fitness and wellbeing. From a commercial poultry breeders perspective, there are ongoing concerns that the limits of selection for growth rate and egg production may be on the horizon. In response the industry will likely place increased emphasis on new sources of genetic variation, and appropriate biomarkers for the genetic improvement of fitness and welfare related traits. Progress through traditional methods of selection has been important for continued long-term economic sustainability of poultry. The development of new nontraditional methods of selection will be necessary for continued improvement in efficiency of production.
Animal Health Component
50%
Research Effort Categories
Basic
20%
Applied
50%
Developmental
30%
Goals / Objectives
OBJECTIVE: Genetic selection for traits of economic importance has often been at the expense of correlated traits such as reproductive efficiency, metabolic disorders and immunological fitness. Limited information is available to describe the genetics inter- relationships or interaction of genes and their subsequent effects on traits. Therefore, the overarching goal of this project is to develop research populations to define physiological, biochemical and gene expression consequences to genetic selection in poultry using both selected and commercial lines. The more specific objectives are:1). To determine the functional mechanisms of genetic changes as a result of selection.2). To determine the effect of genotype by environmental interaction on the biochemical and physiological mechanisms involved in the expression of productive phenotypes.3). Identify and evaluate individual loci on performance phenotypes and genetic background.
Project Methods
Objective 1: To determine the functional mechanisms of genetic changes as a result of selection.Growth-Body Weight: Selection program has been established to determine the effect ofSelection for body weight (BW) or BW gain (BWG) on patterns of growth in quail. Japanese quail lines H10, H17, H28, and H40 have been selected for high rate of growth at 10, 17, 28, or 40 days of age respectively. Line HL has been selected for high growth rate between days 10-17 of age, and low BWG between 17 and 28 d of age. Line LH has been selected for a low rate of growth between 10 to 17 d of age, and a high rate of growth between 17 to 28 d of age. All lines have been selected for 35 generations and distinct patterns of growth. The Ohio State University and University of Georgia both have Japanese quail lines divergently selected for high and low 4-wk BW (HW and LW). These quail lines have been selected for high 4-week body weight for 60 and 100 generations respectively. The weight selected quail lines from these institutions have been combined at the University of Arkansas to produce a heavy random bred population, which will be used for future selection projects. Most recently this heavy random population served as the genetic base for a series of selection studies designed to investigate various methods of selecting for feed conversion including traditional and residual feed intake. This new population will continue to be maintained and routine measurements of selected and correlated traits will be made. The lines are available for use in collaborative studies.Susceptibility and resistance to rous sarcoma: Two Leghorn type populations that have exhibited resistance and susceptibility to Rous sarcoma tumor virus. Gyles et al. (1967) first reported on the development of these two lines (Arkansas Progressor and Arkansas Regressor). The Regressor line typically regressed induced. Rous sarcomas but the Progressor develops a fatal tumor. Since the two lines have been developed, various aspects of their immune system have been investigated. The lines have been characterized and fixed for various MHC blood groups.Ascites: We have developed divergent lines for susceptibility to ascites as induced by hypobaric hypoxia (Anthony and Balog, 2003). The base population for these lines was a commercial elite line that had experienced one generation of relaxed selection. This line is currently maintained with the ascites selected lines. Line selection was accomplished through family selection where sibs were selected based on performance at 9000 feet altitude. Lines are in their 22nd generation of selection and progeny are available for use for cooperatives studies. Current ascites incidence has led to the selection of the resistant line at simulated 12,000 ft. while the susceptible line is now selected at 8000 ft.Muscle: In an effort to determine the genetic component for the breast muscle condition Pale Soft and Exudative (PSE) and Dark Firm and Dry (DFD), we started research lines based on the selection for muscle color using a Minnolta Colorimeter. The trait measured (L-value) was found to be highly correlated with muscle pH and thus associated with tenderness issues often associated with PSE and DFD. We are currently in Generation 14 of this selection study and are now looking at correlated traits and how environment interacts to influence the PSE and DFD condition.Hyperplasia: Many researchers have attempted to identify genetic marker designed to influence the degree of muscle hyperplasia in developing embryos and early post hatch chicks.The hypothesis is simple in that the more muscle nuclei available the greater the opportunity of protein production and thus greater muscle mass later in life. With this in mind, research broiler lines have been divergently selected for 4-day percentage breast yield. This has been identified as an age where maximal muscle has been contributed through hyperplasia. These lines are going into generation 7 and will be explored for direct and correlated responses to selection.Objective 2: to determines the effect of genotype by environment interaction on biochemical and physiological mechanisms involved in the expression of production phenotypes.For all of the research lines described above, we have found that environmental conditions can play an important role in their selected trait response. A major component of my research program therefore, is in the study of dietary and environmental factors on nutrient utilization, requirements, oxidative stress, reproductive and immunological responses among commercial and selected strains of poultry. The questions asked include: What is the impact of genetic selection for economic traits on health, efficiency of nutrient utilization and reproductive performance of domestic poultry? What are the physiological responses to diverse environmental stressors among lines of selected birds?In many cases, our work has debunked myths put into the literature by researchers who have "identified" environmental triggers for a trait response.OBJECTIVE 3: Identify and evaluate individual loci on performance phenotypes and genetic background.The goal of quantitative traits loci (QTL), SNP and microarray studies are to identify genes that affect traits of economic importance. The ultimate goal is to evaluate identified genes for their contribution towards a phenotype. It is essential to work with randomly mating unselected populations with well-defined phenotypes. Random bred lines established by a research team include:Arkansas Relaxed Broiler Line: Previously selected pedigree elite line that has undergone 22 generations of random mating. This line served as the base population for the previously described ascites lines.Arkansas Random bred Broiler Line: This population represents a composite of 6 female and 7 male commercial parent stock available at 1996. They have been random-mated for 9 generations using 24 sire families with 3 dams per sire. The growth and reproductive performance of this random bred line is consistent with industry standards. This line served as the base population for the Muscle quality and 4-day percentage breast yield lines.Giant Jungle Fowl: Random bred population from Siapan that has been maintained in a random bred fashion since the 1940's. This line has served the base population for the Rous Sarcoma lines initiated by Dr. Roy Gyles.Random Bred Quail populations: We currently have 3 random bred Japanese quail lines that have come from different origins. Japanese quail are used for selection studies since they have short generation intervals, easy to handle and are economical to maintain.