Role of Riboflavin in Poultry Nutrition

Role of Riboflavin in Poultry Nutrition: Comparison

Please note this is a comparison between Version 1 by Yauheni Shastak and Version 2 by Lindsay Dong.

Riboflavin, an essential B-vitamin, plays a crucial role in poultry metabolism, impacting energy production, growth, and immune regulation. Its role in redox reactions and energy metabolism is vital for optimal growth and development. Riboflavin is essential for adenosine triphosphate (ATP) production and the conversion of tryptophan into niacin. Deficiency can lead to skeletal deformities, impaired growth, and compromised immune function. Dietary riboflavin supplementation is necessary due to variable bioavailability in plant-derived sources. The vitamin is absorbed through specialized transport proteins, and its cellular uptake is facilitated by specific receptors. Riboflavin’s role in protein synthesis and its antioxidant properties influence poultry growth and defense against oxidative stress. Its impact on reproductive performance, hatchability, and overall poultry health underscores its significance in poultry nutrition.

riboflavin
vitamin B2
supplementation
poultry

1. Introduction

In the ever-evolving landscape of poultry farming, the critical role of nutrition in maximizing productivity and promoting avian health has gained significant attention. Domestic fowl, specifically chickens, turkeys, geese, and ducks, hold a paramount position in the global animal protein industry, meeting the rising demand for affordable and nutritious protein sources. Forecasts indicate that by 2031, approximately 47% of the protein sourced from meat will stem from poultry, overshadowing pig, sheep, and bovine meat consumption [1]. Within the intricate web of micronutrients necessary for poultry well-being, the B-vitamins, a group of water-soluble compounds, play a vital role in various physiological processes ^[2][3][2,3]. Among these, riboflavin, also known as vitamin B₂, emerges as a pivotal player in maintaining metabolic equilibrium, ensuring optimal growth and safeguarding the health of poultry ^[4][5][6][7][4,5,6,7]. The recognized nomenclature by the International Union of Pure and Applied Chemistry (IUPAC) for riboflavin is 6,7-dimethyl-9-(D-ribityl)isoalloxazine.

Riboflavin, standing prominently as one of the eight essential B-vitamins, assumes an unparalleled role due to its involvement in an extensive array of metabolic reactions that constitute the foundation of life ^[8][9][8,9]. Functioning as a critical coenzyme precursor, vitamin B₂ orchestrates pivotal redox reactions, contributing indispensably to the intricate processes of energy production, growth facilitation, and the coordination of immune responses ^[10][11][10,11]. As modern poultry production systems witness an intensification in their practices and the demand for poultry-derived products continues its upward trajectory, the imperative for an all-encompassing grasp of micronutrient prerequisites amplifies manifold. In this context, riboflavin emerges as a linchpin micronutrient, capable of exerting far-reaching impacts on poultry performance and holistic well-being ^[12][13][12,13].

Central to the matter lies the astounding metabolic demands of poultry, characterized by rapid growth kinetics and inherent production prowess, necessitating substantial nutritional resources [14]. Vitamin B₂ is a precursor for two important coenzymes: flavin mononucleotide (FMN), involved in the mitochondrial electron system, and flavin adenine dinucleotide (FAD), associated with various proteins in redox reactions [15]. These redox reactions are pivotal for the breakdown of carbohydrates, fats, and proteins, culminating in the production of adenosine triphosphate (ATP), the cell’s primary energy currency [16]. Deficiency in this essential micronutrient could disrupt balanced metabolic functioning in poultry, resulting in delayed growth, skeletal deformities, and worsened feed conversion efficiency, a critical metric in poultry farming ^[8][17][8,17]. Frequent clinical indications encompass limping, paralysis, toes curling inward, and elevated culling rates [17]. As riboflavin insufficiency reverberates through metabolic pathways, its consequences extend even to immunity ^[18][19][18,19].

This escalating complexity propels riboflavin to the forefront of nutritional concerns in the poultry sector. The intricate interplay between this seemingly unremarkable vitamin and the complex pathways of metabolism surpasses mere scientific curiosity, holding direct economic implications for poultry production ^{[13][20][21][22][23][24][25][26]}[13,20,21,22,23,24,25,26]. Riboflavin’s dual role as a conductor of energy dynamics and an architect of growth processes underscores the delicate equilibrium underlying poultry nutrition. By elucidating how vitamin B₂ shapes metabolic landscapes and influences avian health, nutritionists, researchers, and poultry producers can advance towards enhanced sustainability and efficiency in the industry’s landscape. As the poultry industry continues its ascendancy [27], riboflavin’s centrality as a cornerstone of avian nourishment becomes increasingly pronounced [9].

2. Biochemical Fundamentals of Riboflavin

Riboflavin plays a key role in the fundamental biochemical processes that sustain avian life. Its significance arises from its multifaceted functions as a coenzyme in a variety of metabolic reactions, notably those involving redox reactions and energy metabolism ^[15][26][15,26]. To grasp the biochemical underpinnings of riboflavin’s role in poultry health, it is imperative to delve into the intricate details of its molecular structure and its coenzyme derivatives, namely FMN and FAD. Furthermore, comprehending its key functions within the avian system, encompassing its involvement in redox reactions and facilitation of energy metabolism, illuminates its indispensability for optimal growth and development. At its core, riboflavin comprises a heterocyclic ring system, consisting of a central isoalloxazine ring intricately linked to a ribitol side chain ^[10][28][10,37]. This distinctive chemical arrangement enables riboflavin to serve as a precursor to its coenzyme derivatives, FMN and FAD ^[29][38] (Figure 1). FMN is synthesized through the phosphorylation of riboflavin catalyzed by riboflavin kinase in the presence of ATP:Mg²⁺. This conversion represents a major rate-limiting step in FAD biosynthesis ^[30][39]. FAD formation occurs as FMN:ATP adenylyl transferase catalytically adenylylates FMN to produce FAD ^[31][40]. FMN and FAD are tightly associated with enzyme cofactors that can either accept or donate two electrons and two protons to achieve full reduction or a single electron and proton to form the semiquinone intermediate ^[32][41]. This coenzyme system facilitates electron transfer during biochemical reactions, establishing riboflavin as an indispensable component in enzyme-catalyzed oxidation reduction processes in avian species as well as mammals ^[26][33][26,42].

Figure 1. Chemical structure and nomenclature of flavins (Liu et al. ^[29][38]). RF = riboflavin; FMN = flavin mononucleotide; FAD = adenine dinucleotide; AMP = adenosine monophosphate.

Fundamentally, the biochemical functions of riboflavin in poultry are intricately linked to its role as a coenzyme in redox reactions ^[34][29]. These reactions play a crucial role in maintaining the delicate equilibrium between the oxidized and reduced states of molecules within the cellular environment. The coenzymes of riboflavin, namely FMN and FAD, play an active role in these reactions by functioning as carriers of electrons ^[32][41]. When enzymes facilitate reactions involving electron transfer, the coenzymes FMN and FAD alternate between their oxidized and reduced states, effectively shuttling electrons to and from the reaction site ^[35][36][43,44].

This unique ability to mediate electron transfer is particularly crucial in enzymatic reactions taking place within the mitochondria—the cellular powerhouses. This is where oxidative phosphorylation occurs ^[37][38][45,46]. Given this backdrop, riboflavin’s coenzymes serve a vital role in the electron transport chain, an integral process for generating ATP ^[39][28].

In the context of energy metabolism, riboflavin’s significance cannot be overstated. Poultry, like all living organisms, requires energy for various physiological processes, including growth, maintenance, and reproduction. Riboflavin’s involvement in energy metabolism primarily stems from its participation in the electron transport chain ^[26][39][26,28] (Figure 2).

Figure 2. Schematic diagram of flavocoenzymes in mitochondrial energy metabolism (Balasubramaniam et al. ^[39][28]). “The OXPHOS system is a 5-enzyme complex which encompasses the mitochondrial respiratory chain (Complexes I-IV), Complex V, and two mobile electron shuttles (coenzyme Q10 and cytochrome c). Electrons derived from oxidation of pyruvate mediated by pyruvate dehydrogenase (PDH) and fatty acid oxidation are transferred via NADH to Complex I (FMN-dependent NADH-ubiquinone oxidoreductase), while electrons from succinate in the Krebs cycle, amino acid metabolism, and fatty acid oxidation are transferred to Complex II (FAD-dependent succinate-ubiquinone oxidoreductase) via FADH₂. Electrons are subsequently transferred to ubiquinone (Coenzyme Q10) and then to Complex III (reduced CoQ-cytochrome c reductase), and via cytochrome c to cytochrome c oxidase (COX) (Complex IV), the terminal oxidase of the RC before finally reducing molecular oxygen to water. The free energy liberated during this sequential electron transfer is used to generate an electrochemical gradient of protons, which is finally used by Complex V (ATP synthase or F1F0 ATPase) to drive ATP synthesis from ADP and inorganic phosphate. RF: Riboflavin; RF kinase: riboflavin kinase; Q: Coenzyme Q10; CytC: cytochrome c oxidase; FMN: flavin mononucleotide; FAD: flavin adenine dinucleotide”.

Moreover, riboflavin’s influence on energy metabolism extends beyond its impact on mitochondria; it assumes a central role in the intricate processing of macronutrients such as carbohydrates, lipids, and proteins ^[40][51]. Notably, riboflavin-dependent enzymes referred to as dehydrogenases actively participate in the oxidation of glucose and fatty acids ^[41][42][52,53]. This oxidative process stands as a pivotal stage in harnessing energy from these substrates. Furthermore, riboflavin is a key player in the conversion of the amino acid tryptophan into niacin, an essential B-vitamin ^[43][44][54,55].

3. Riboflavin Metabolism in Poultry

Understanding the metabolism of riboflavin in domestic fowl is vital for ensuring optimal health, growth, and production in these birds. The journey of vitamin B₂ in poultry begins with its absorption, transport, and subsequent tissue distribution.

The absorption mechanism of riboflavin predominantly takes place within the small intestine of domestic fowl ^[45][59]. This intricate process commences with the liberation of riboflavin from dietary sources. Common constituents of poultry diets, such as grains and protein-rich meals, contain varying concentrations of vitamin B₂ ^[46][47][48][60,61,62]. As elucidated by Merrill et al. ^[49][63], the major portion of riboflavin in feed materials exists in the form of free coenzymes—FMN and FAD—the predominant being FAD. The availability of riboflavin to the avian system necessitates its prior release from these coenzymes, which is facilitated by gut pyrophosphatases and phosphatases ^[50][64].

Due to the inherent variability in the vitamin B₂ content of plant-derived ingredients, coupled with factors leading to variable bioavailability and occasional degradation, the supplementation of fermentation-synthesized riboflavin via premixes becomes essential to fulfill the vitamin’s requirements in animal nutrition ^{[50][51][52][53][54]}[35,36,64,65,66]. Industrially produced riboflavin, being in a non-esterified form, can be directly absorbed without the need for a hydrolysis step, which is necessary for plant-derived native vitamin B₂.

Following liberation from feed particles, riboflavin emerges into an aqueous environment within the digestive tract, undergoing solubilization to facilitate subsequent absorption. The loss of biosynthetic pathways for most vitamins in the ancestors of vertebrates led to the development of mechanisms such as specialized transport proteins ^[55][68]. These proteins aid in the uptake of dietary vitamins from both the intestine and serum ^[56][69]. In the case of vitamin B₂, a crucial step in its intestinal absorption involves active transportation across epithelial cells via specialized riboflavin transporters, ensuring the efficient flux of the vitamin into the bloodstream [19]. Under physiological concentrations, riboflavin is taken up through an active and saturable transport mechanism ^[57][70].

Vitamin B₂ transportation within poultry species is facilitated by its association with specialized transport proteins, ensuring its equitable dispersion throughout the avian organism ^[58][59][73,74]. In these species, riboflavin is conveyed via the circulatory system, serving as the conduit for its movement. An instrumental component in this mechanism is the chicken riboflavin-binding protein (RBP), a phosphoglycoprotein weighing 29.4 kDa ^[60][61][62][75,76,77]. The pivotal role of RBPs lies in safeguarding riboflavin from degradation, facilitating its secure transfer to diverse tissues ^[56][69]. By means of the RBP-mediated process, a consistent supply of vitamin B₂ is assured to organs and tissues reliant on this vital micronutrient for optimal functioning.

The gene responsible for producing egg white, yolk, and serum RBPs is shared, exhibiting slight tissue-specific disparities in post-translational modifications ^[55][68]. RBPs are synthesized by the liver or oviduct in poultry and subsequently released into the bloodstream or eggs ^[26][63][26,78]. The mature and functional form of RBP undergoes initial post-translational modifications ^[58][73]. This entails cleavage of an unidentified signal peptide, blockade of its amino terminus with pyroglutamic acid, and excision of an 11-13-residue acidic carboxyl-terminal peptide during or after transportation ^[64][79].

The cellular uptake process of riboflavin involves the transport of the vitamin across the plasma membrane via specific receptors called riboflavin transporters, following its release from the plasma through the RBP ^[63][78]. This mechanism relies on a calcium-ion-dependent RBP receptor, situated within clathrin-coated pits on the phospholipid bilayer ^[65][82]. This receptor serves as a catalyst for the endocytosis of the vitamin B₂, enabling its subsequent internalization and release ^[63][78].

The distribution of vitamin B₂ in various tissues provides valuable insights into its significance in avian metabolism, particularly its involvement in enzymatic reactions. Riboflavin plays a critical role as a precursor to two essential coenzyme forms: FMN and FAD ^[29][38]. Tissues with elevated energy demands, such as muscle and liver, exhibit higher concentrations of riboflavin due to their reliance on FMN and FAD ^[66][67][68][83,84,85].

4. Riboflavin and Poultry Growth

An important observation from the first half of the 20th century is that riboflavin was designated as the “growth-promoting vitamin G” ^{[69][70][71][72][73][74]}[90,91,92,93,94,95]. This recognition is rooted in riboflavin’s involvement in a multitude of physiological processes intricately linked to the overall growth performance of domestic fowl species. Within this complex web of biological interactions, vitamin B₂ significantly influences pivotal factors that contribute to poultry growth, including nutrient utilization, protein synthesis, and enzyme activity ^{[7][72][75][76]}[7,30,93,96]. The interrelation between vitamin B₂ and nutrient utilization constitutes a fundamental aspect in comprehending its influence on poultry growth. Riboflavin serves as a cofactor for enzymes engaged in the metabolic pathways responsible for the degradation of carbohydrates, lipids, and proteins ^[10][77][10,97]. Through facilitation of these enzymatic reactions, riboflavin indirectly enhances the efficacy of nutrient breakdown and absorption within the avian gastrointestinal tract [26]. This, in turn, culminates in a heightened extraction of energy and nutrients from the ingested feed, thereby furnishing the essential foundational components required for optimal growth. The amelioration in nutrient utilization serves as a principal catalyst underpinning the growth-promoting ramifications of riboflavin across diverse poultry species ^{[25][70][75][78]}[25,30,91,98]. The Tricarboxylic Acid cycle (TCA) holds pivotal significance in the growth of living organisms, as it induces energy production, furnishes foundational constituents, and upholds redox equilibrium ^[79][99]. FAD and FADH₂, integral to the TCA cycle, assume a pivotal role by engaging in redox reactions that contribute to energy synthesis and streamlined growth processes ^[80][100]. Dysfunction within this cycle or disruptions in FAD/FADH₂ participation can impede growth-associated pathways and cellular functionality. Shifting focus beyond nutrient utilization, the significance of riboflavin in protein synthesis emerges as a pivotal factor in promoting poultry growth. The process of protein biosynthesis, fundamental to the development of muscles, tissues, and bodily structures in both mammals and avian species, involves riboflavin. Specifically, vitamin B₂ plays a role in the folding of newly synthesized proteins within the endoplasmic reticulum, facilitated by an FAD-dependent enzyme called endoplasmic reticulum oxidoreductase 1 ^[81][82][101,102]. Hypovitaminosis B₂ can potentially disrupt this protein folding process due to diminished flavoproteins and an imbalanced redox state, triggering a stress response within the endoplasmic reticulum ^[82][102]. Empirical evidence supporting the influence of riboflavin on domestic fowl growth is substantial and compelling. Diverse experiments across various poultry species have been conducted to explore the impact of vitamin B₂ supplementation on growth performance ^{[4][5][8][13][17][25][69][70][71][72][73][74][78][83]}[4,5,8,13,17,25,33,90,91,92,93,94,95,98].

5. Oxidative Stress Defense

Oxidative stress, characterized by an imbalance between the production of reactive oxygen species (ROS) and cellular detoxification mechanisms, presents a significant challenge to domestic fowl health and productivity ^[84][58]. Avian cells have developed an intricate defense network to counter this threat, with riboflavin emerging as a pivotal component in this system [11]. Recent investigations have unveiled an additional dimension to riboflavin’s role—its function as a potent antioxidant within animal cells ^[75][30]. This discovery underscores its critical contribution to ROS neutralization and cellular protection, rendering it indispensable in poultry’s defense against redox imbalance [26]. The complex metabolic processes inherent to avian cells inevitably lead to the generation of ROS as natural by-products. While ROS serve important physiological roles, their excessive accumulation triggers oxidative stress, inducing damage to lipids, proteins, and nucleic acids ^[85][119]. Such cellular damage disrupts vital functions, compromises immune responses, and fosters the onset of diverse poultry ailments ^[84][58]. Central to riboflavin’s role as an antioxidant is its active involvement in the glutathione redox cycle. Glutathione, a robust tripeptide antioxidant, plays a pivotal role in defending against damage induced by ROS. Vitamin B₂ contributes to this cycle by facilitating the activity of glutathione reductase. This enzymatic action promotes the regeneration of reduced glutathione from its oxidized state, as detailed by Suwannasom et al. [10]. The significance of riboflavin’s robust antioxidant capabilities becomes notably more conspicuous when contextualized within the contemporary landscape of poultry farming. Modern techniques of poultry production expose avian species to an assortment of stress-inducing factors, encompassing elevated temperatures, pathogenic microorganisms, and environmental pollutants. These factors collectively contribute to an exacerbation of oxidative stress conditions ^[84][86][58,123].

6. Reproductive Performance and Hatchability

Reproductive performance and hatchability constitute pivotal determinants within the poultry industry, wielding substantial influence over egg production efficiency and the overall triumph of poultry farming ^[87][127]. One elemental factor that has been extensively scrutinized in relation to these parameters is riboflavin. The impact of vitamin B₂ on reproductive variables such as egg production, egg quality, and hatchability has elicited considerable attention from both researchers and poultry producers ^{[11][12][26][88][89][90][91][92][93]}[11,12,26,56,109,118,128,129,130]. Through an array of studies, it has been unequivocally demonstrated that a dearth of riboflavin can exert a substantial impact on poultry reproductive success, carrying profound ramifications for both economic and bird welfare considerations. Hatchability, a critical parameter in poultry farming, is significantly influenced by riboflavin status ^{[94][95][96][97]}[132,133,134,135]. In fact, hypovitaminosis B₂ emerges as one of the prevalent nutritional insufficiencies capable of influencing the hatching process ^[98][136]. The various developmental stages of an embryo within an egg demand a consistent supply of nutrients and energy. Riboflavin’s role in cellular energy generation through its participation in the electron transport chain bears a direct connection to embryonic development and viability ^[99][100][137,138]. A lack of riboflavin during incubation can lead to impaired growth and development of the embryo, ultimately resulting in reduced hatchability rates ^[101][139]. Moreover, riboflavin’s impact on reproductive success can also be attributed to its involvement in cellular growth and differentiation. Vitamin B₂ plays a crucial role in maintaining the integrity of cell membranes through its participation in lipid metabolism and the regulation of oxidative stress ^{[11][82][102]}[11,102,145]. Riboflavin deficiency can disrupt cellular membrane structure and function, affecting the development and viability of reproductive cells ^[102][145]. This disruption may potentially yield impaired follicle development, disrupted ovulation, and compromised sperm and oocyte quality, ultimately influencing hatchability rates.

7. Riboflavin Requirements for Poultry

The recommended dietary requirements for vitamin B₂ vary among different poultry species and at different stages of their production cycle, reflecting the dynamic nature of avian growth and development. In broiler chickens, for instance, riboflavin needs are influenced by their rapid growth during the fattening phase [25]. This phase, characterized by rapid muscle and skeletal development, necessitates increased riboflavin intake, along with other essential vitamins, to support energy metabolism and tissue repair ^[103][148]. Conversely, when considering laying hens during their peak egg production phase, distinct vitamin B₂ requirements emerge ^[11][88][11,56]. Beyond species and production stages, riboflavin requirements are intricately tied to feed composition [13]. The delicate interplay between vitamin B₂ and other nutrients underscores the importance of a balanced diet ^[50][64]. Poor-quality feeds can hinder riboflavin absorption and utilization, leading to deficiencies despite adequate dietary levels. Additionally, stressors, drug usage, and disease challenges amplify avian metabolic demands, prompting heightened vitamin requirements ^[51][35]. It is crucial to distinguish between vitamin B₂ requirement estimates and allowances as determined by scientific committees such as the National Academies of Sciences, Engineering, and Medicine ^[104][149] (formerly known as the National Research Council), the Gesellschaft für Ernährungsphysiologie (GfE) ^[105][150], and recommendations from poultry breeding companies like Aviagen, Cobb-Vantress, and Lohmann ^{[106][107][108][109]}[153,154,155,158]. Poultry producers often refer to both sources to strike a balance between scientific knowledge and the specific genetic potential of their flocks. In contemporary times, there is a growing acknowledgment that the vitamin requirements for commercial poultry production may surpass the previously established levels for healthy birds in controlled research settings, as outlined by organizations like NASEM ^[110][71]. Stress, infections, and illnesses can substantially elevate the vitamin needs of birds, factors that must be taken into account in real-world farming scenarios ^[111][166]. Riboflavin’s involvement in cellular growth and repair mechanisms underscores its significance during the rapid growth phase of poultry. Skeletal development, a complex process of bone formation and remodeling, relies heavily on vitamin B₂-mediated energy transactions. As chicks develop their skeletal framework at a rapid pace, the mineralization process depends on the energy generated through riboflavin-supported metabolic pathways ^[112][167]. This not only influences bone strength but also contributes to the overall structural robustness of growing birds. Hypovitaminosis B₂ can lead to an increase in deformed legs and poor mobility in broilers ^[113][117]. Citrate, which comprises approximately 1.6% of bone content and about 80% of total body citrate residing in bones, plays a crucial role in bone stability, strength, and resistance to fracture ^[114][168]. Riboflavin in its coenzyme form FAD is critical for the normal functioning of the citric acid cycle, which is presumed to be a key supplier of citrate for the bone’s apatite nanocrystal structure ^[114][168]. This occurs through the prevention of citrate oxidation via the Krebs cycle in some bone cells, maximizing citrate accumulation ^[114][168].

8. Conclusions

Riboflavin plays a crucial role in the field of poultry nutrition and health. Its diverse functions as a coenzyme in various metabolic reactions, particularly in redox reactions and energy metabolism, emphasize its indispensability in avian physiology. Vitamin B₂ significantly contributes to enhancing nutrient utilization, facilitating protein synthesis and folding, and promoting enzyme activity. These roles collectively support optimal growth and performance in domestic fowl. Moreover, the impact of riboflavin on reproductive parameters, such as egg production, egg quality, and hatchability, cannot be overstated. Its involvement in energy metabolism and antioxidant defense mechanisms directly influences the reproductive success of avian species, with far-reaching implications for both economic viability and animal welfare considerations. Exploring riboflavin’s interactions with other essential nutrients, investigating the potential of riboflavin analogs as antimicrobial agents, and embracing advanced technologies like precision nutrition and nanotechnology for improved riboflavin delivery represent promising avenues for future research in poultry nutrition.