Based on Darwin’s theory of adaptive evolution and Mendel’s fundamental laws of heritability, breeding and genetic selection for increased growth rate and meat yield has dramatically advanced the production efficiency of poultry during the last 50 years, and this trend is expected to continue well into the future.
Now, the period of embryonic and neonatal development is approaching 50% of the productive life of modern broilers, turkeys, and ducks. Although genetic selection does dictate how maternal and paternal genes that are inherited by their progeny, we are becoming more aware that nutrition and management may influence how those inherited genes are expressed. Epigenetics is the rising science of programming gene expression during critical developmental periods, which subsequently allow an animal to metabolically or physiologically adapt to specific dietary or environmental conditions. In poultry, epigenetic programming can occur during two critical periods: during the period of gametogenesis when breeding stock are adolescents, and during egg formation when egg nutrients are consumed by the embryo via amniotic fluid prior to hatch and yolk through to the first few days after hatch. Adaptive conditioning can be advanced further by nutritional or physiological imprinting during the first days after hatch. This paper discusses implications of nutritional and physiological stress of breeders on the epigenetic response of progeny, and how it can be modified by perinatal nutrition, including amniotic fluid supplementation by in ovo feeding and early feeding technologies. Epigenetic and adaptive conditioning of neonatal nutrition will also be discussed in the context of a “programmed nutrition” strategy to increase production efficiency and meat quality. As new molecular biology tools to measure gene expression become increasing affordable and robust, the study of epigenetic programming by perinatal nutrition will become an increasingly popular field of research. Moreover, emerging perinatal nutrition technologies for hatcheries will likely make programmed nutrition a commercial reality in the future as genetic selection for performance efficiency continues.
Modern agriculture constantly strives to maximize biological performance of food production in an effort to optimize economic efficiency, profit potential, and sustainability. Commercial poultry production is among the most efficient and progressively successful of all food production sectors. What factors does it take for continued success in efficient poultry production? It takes the right genetics, combined with optimum health and management practices, and an optimized nutrition and feeding program. Efficiency and sustainability depends on the ability of a poultry production company to achieve competitive production indicators, including average daily gain, days to market weight, feed (caloric) conversion, livability, flock uniformity, and processing yields. However, profitability largely depends on how well a poultry production company meets consumer demand. Consumers want wholesome, safe, and affordable food. They want poultry products that look good, and are enjoyable to eat. Moreover, the most affluent consumers also want to buy their food from companies that excel in environmental stewardship and animal welfare. After proper management of commercial genetic stock, nutrition and feed is the most variable component of economic efficiency and profitability, as it represents 70 to 80% of live production costs.
Genetic selection is continually changing the “playing field” of production potential for the poultry industry; but it is the expression of this genetic potential that drives growth performance, health, and ultimately the profitability of poultry production. Growth performance and meat yield has improved linearly by about 1% each year, and 85% of this improvement is attributed to genetic selection of broilers and turkeys. One may argue that nutritional advancements have not kept pace with genetic selection as metabolic disorders and apparent nutritional deficiencies continue to arise, which mandate diet formulation constraints to be updated. However, the time has come to close this pace gap as we learn to harness the power of perinatal nutritional imprinting and adaptive conditioning to program the expression of genes associated with socioeconomically important traits.
The ancient Greek philosopher, Aristotle, theorized an individual’s traits are acquired from their parents and contact with their environment. In simple terms, Aristotle’s theory of developmental destiny means that all life on this planet is programmed to succeed in its given environment. Just a generation before Mendel’s time, Jean Lamark was a proponent of the inheritance of acquired characteristics. The so-called Lamarckism theory emphasized the use and disuse of organs as the significant factor in determining the characteristics of an individual, and it postulates that any alterations in the individual could be transmitted to the offspring through the gametes. Despite many attempts, this inheritance of acquired characteristics has never been experimentally verified. Furthermore, many of Lamarck’s examples, such as the long neck of the giraffe, can be more satisfactorily explained by means of natural selection.
The academic discipline of genetics has followed Mendel’s basic concepts for over a century, and it was reinforced by the discovery and sequencing of DNA. Genetics describes the inheritance of information on the basis of DNA sequence. As the DNA sequence fragments were scientifically associated with certain biological traits, genomic scientists began to realize the importance of the gene expression. It was not until the recent introduction of molecular biological tools that the science of epigenetics and conditional imprinting has emerged. We can now study gene expression by mRNA up-regulation, proteomics and metabolonics. Now, many molecular geneticists agree that gene expression in response to environmental cues can be passed on to future generations. The old Greek philosophers and Jean Larmarck may have been right after all; they just did not have the scientific tools to prove it. There is now growing evidence that nutrition and environmental stimuli of parent stock and their progeny during the perinatal period may literally program how an animal’s genes are expressed as an adaptive response to increase the chances of survival. This new science of “gene expression programming” is Epigenetics; it is the inheritance of information on the basis of gene expression, or inherited adaptation.
What is epigenetic or adaptive conditioning?
Epigenetics literally means “on genes”, and refers to all modifications to genes other than changes in the DNA sequence itself. DNA within each cell is wrapped around proteins called histones. Both the DNA and histones are covered with chemical tags, to form what is called the epigenome. These chemical tags react to signals to the outside world, such as diet and stress. Some parts of the epigenome are wrapped and unreadable, and other parts are relaxed and readable for expression. Epigenetic imprinting of genes occurs most often by differential methylation of DNA at the promoter regions of specific genes that can permanently modulate an organism’s adaptive response to adverse stimuli during critical periods of development. Particularly, early-life programming can turn on “Thrifty” genes that permanently reprogram normal physiological responses to survive environmental stressors, including moderate nutrient deficiency, and thus increase the chances of passing on their genes to the next generation. Evidence for epigenetic programming is demonstrated by swarming locusts: the swarming phenotype is environmentally influenced by drought conditions and the trait is passed onto the next generation until the population finds better conditions. Trans-generational epigenetic or adaptive conditioning may explain some of the blessings and curses observed as a result of our system of commercial poultry production. Consider how we manage the weight of broiler or turkey breeders before and during egg production: this is during the critical epigenetic period of gametogenesis. Broiler breeder nutrition and feeding management likely has an important epigenetic effect on progeny. Consider how we manage and incubate commercial hatching eggs: this is during the critical epigenetic period of de novo methylation of somatic cells in the embryo. Environmental conditions (i.e. temperature and oxygen concentration) in the incubator may program epigenetic responses that affect subsequent metabolism. Consider how we manage chicks during the first few days after hatch. Feeding behavior, nutrition, and brooding conditions can affect metabolism and the development of breast muscle, the skeleton, and immune system.
In Ovo feeding jump-starts perinatal development
Phenotypic characteristics that are programmed or imprinted to succeed in it’s given environment and diet happen most effectively when the animal is young, and it is the first few meals that usually make the difference. For example, all honeybees are genetically similar, but what predestines a bee to become a worker or a queen is what the larvae are fed. Likewise, poultry may be programmed to succeed with the desired phenotypic traits by nutritional modification during the perinatal period: the 3 days before hatch and the 3 days after hatch. The chick’s first meal occurs when it imbibes the amnion prior to hatch, and so this is the first opportunity for nutritional programming. By in ovo feeding, nutrient balance and key metabolic co-factors of the amnion meal can be modified and influence subsequent phenotypic traits of economic importance for the poultry industry.
The benefits of in ovo feeding on early growth and development of broilers and turkeys have been demonstrated by several experiments in our laboratory. In ovo feeding has increased hatchling weights by 3% to 7% (P<.05) over controls, and this advantage is often sustained at least until 14 days post-hatch. The degree of response to in ovo feeding may depend upon genetics, breeder hen age, egg size, and incubation conditions (i.e. the epigenotype). Above all, IOF solution formulation has the most profound effect on the neonate. Positive effects have been observed with IOF solutions containing NaCl, sucrose, maltose, and dextrin, β-hydroxy-β-methyl butyrate, egg white protein, and carbohydrate, Arginine, zinc-methionine, butyric acid, IGF-1, and L-glutamine. In addition to the increased body weights typically observed at hatch, the positive effects of in ovo feeding may include increased hatchability; advanced morphometic development of the intestinal tract and mucin barrier; enhanced expression of genes for brush boarder enzymes (sucrase-isomaltase, leucine aminopeptidase) and their biological activities, along with enhanced expression of nutrient transporters, SGLT-1, PEPT-1, and NaK ATPase (increased liver glycogen status; enhanced feed intake initiation behavior; increased breast muscle size at hatch, breast muscle growth and meat yield, and improved skeletal development). In ovo feeding clearly advances the digestive capacity, energy status, and development of critical tissues of the neonate by about 2 days at the time of hatch. Using scanning electron microscopy, Bohórquez et al. (2008) observed that in ovo feeding significantly increased functional maturity and mucus secretion of goblet cells of villi of ileum and ceca of turkey poults. Associated with these goblet cells was the colonization of lactobacilli. Therefore, in ovo feeding may help improve the colonization resistance of enteric pathogens of neonatal chicks and poults. Based on the rapidly growing number of peer-reviewed publications from around the world, in ovo feeding consistently shows promising benefits, especially if applications can be done without compromising hatchability. In ovo feeding offers promise of sustaining the progress in production efficiency and welfare of commercial poultry. Although selection for fast growth rate and meat yield may favor the modern broiler to become a more altricial, proper early nutrition and in ovo feeding may help these birds adapt to a carbohydrate-based diet and metabolism typical of a precocial bird at hatch. Our original research on in ovo feeding has established a new science of neonatal nutrition that many other scientists are now pursuing. As a result, we are all gaining greater understanding of the developmental transition from embryo to a juvenile bird. Now more work on in ovo feeding application technology and hatchery logistics must be done before in ovo feeding can be widely adopted for commercial practice.
Potential of post-hatch nutrition on nutritional imprinting
The first few days post-hatch is the second part of the perinatal period that can imprint production traits by adaptive conditioning of gene expression. Chicks can be imprinted to enhance their tolerance to immunological, environmental, or oxidative stress. Nutritional programming during the perinatal period can also influence energy and mineral utilization or requirement, while other bioactive dietary components may “program” enteric microflora colonization that affect gut health and food safety. For example, Yan et al. (2005) reported that conditioning broilers fed a diet low in calcium and phosphorus for 90 hours post-hatch improves intestinal calcium and phosphorus absorption at 32 days of age, and increases the expression of the gene for the mineral transporter protein throughout the life of the bird. Angel and Ashwell (2008) demonstrated that broilers fed a moderately deficient conditioning diet for the first 90 hour post-hatch were more tolerant to a P-deficient grower and finisher diet, but they were also heavier, had better feed conversion, and they had higher tibia ash and P retention. The work of Angel and Ash-well demonstrate that epigenetic imprinting and nutritional adaptation to low dietary Ca and P is indeed possible and likely for other minerals as well. Based on the concepts of epigenetics, imprinting, and adaptive conditioning presented above, several experiments has been done to test various nutritional programming strategies at the Alltech University of Kentucky Nutrition Research Alliance Coldstream Farm and Alltech’s Center for Animal Nutrigenomics and Applied Animal Nutrition. By evaluating the expression patterns of key functional gene groups, dietary amounts of nutrients that affect homeostatic balance were discovered to depend on the form of the nutrient, levels of and interactions among nutrients, and the timing of administration. Feeding chicks a specifically-formulated diet during the first 72 hours post-hatch has been developed to “condition” the gut for better nutrient utilization and program metabolism that ultimately affects production efficiency, carcass composition, and meat quality. Chicks that have been fed the appropriate conditioning diet, followed by a complementary growing and finishing diet, have improved growth performance and feed efficiency through to market age, and over 70% higher calcium and phosphorus digestion than controls. A programmed nutrition strategy can literally change the nutrient requirement and production efficiency, and may yield a response greater than any single feed additive on the market. Not only can programmed nutrition increase production efficiency that is so important to poultry producers, there is evidence that it improves the meat quality consumers demand, which yields greater potential profits from the poultry products produced. Broilers that have been raised on a programmed nutrition strategy have reduced carcass fat and produce breast meat that has more appealing color, less drip losses during storage, improved oxidative stability, and lower cooking losses.
Although feeding broilers a special nutritional conditioning diet for just 72 hours after hatch presents great opportunities, it is logistically difficult to accomplish in practice using current production systems. Moreover, variation in the time and stress exposure between hatch-pull and placement will affect the effectiveness of the 3-day nutritional conditioning period. However, recent hatch-brood technology offers a practical means to deliver specially formulated diets during the first 2 or 3 days post-hatch in the controlled environment of a hatchery. The hatchery of the future will be a place that will do much more than simply hatch and vaccinate chicks: it will also be the place where the chicks will be conditioned better tolerate the challenges of life, and be programmed for optimum nutrient efficiency. Nutritional science is no longer a matter of supplying minimally required nutrients in the ideal balance to achieve desired production and welfare goals.
From the The Proceedings of XXV World’s Poultry Congres