Vitamin B2
A Metabolic Catalyst for Poultry Growth and Vitality
Yauheni Shastak and Wolf Pelletier
BASF SE, Nutrition & Health Division
67063 Ludwigshafen am Rhein, Germany
Riboflavin, or vitamin B2, is pivotal in poultry nutrition, impacting metabolism, growth, and overall health. Its importance has surged due to increased poultry product demand and intensification of poultry farming. This vital water-soluble vitamin acts as a precursor to crucial coenzymes, essential for redox reactions and energy metabolism. Inadequate riboflavin levels can lead to stunted growth, skeletal deformities, and decreased feed efficiency, impacting poultry performance and profitability. Riboflavin also influences protein synthesis, enzyme activity, nutrient utilization, and reproductive success, affecting egg production and hatchability (Table 1). Tailoring dietary recommendations to different poultry species and genetic advancements is crucial for balanced supplementation and sustainable growth. Exploring riboflavin’s facets empowers experts to improve poultry nutrition, aligning with industry demands.
Table 1. Functions of riboflavin
Function Description
Redox reactions and energy production
Antioxidant capacity
Metabolism of fats, drugs, and steroids
Cellular function, growth, and development
Reproductive functions
Nerve function
Riboflavin is essential for producing energy via two key coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).
Riboflavin possesses indirect antioxidant properties, aiding in the neutralization of harmful free radicals within the body.
Riboflavin participates in the enzymatic reactions associated with the metabolism of lipids, xenobiotic substances, and steroid compounds.
Riboflavin plays a fundamental role in the regulation of cellular functions, growth, and developmental processes.
Riboflavin is essential for the reproductive performance of poultry. It affects fertility, embryonic development and hatchability.
Riboflavin deficiency has been associated with peripheral nerve demyelination in poultry, resulting in symptoms such as leg weakness and curled toe paralysis.
Metabolism of Vitamin B2 in Poultry
Reference
Balasubramaniam et al. (2020); Poudel et al. (2022)
Ashoori and Saedisomeolia (2014), Olfat et al. (2022), Zhang et al. (2020)
Alagawany et al. (2020)
Cogburn et al. (2018)
Cogburn et al. (2018); Zhang et al. (2020)
Johnson and Storts (1988); Cai et al. (2023)
It is essential to understand the metabolism of riboflavin in domestic fowl to ensure optimal health, growth, and production. The process of its absorption begins in the small intestine (Cordona and Payne, 1967). Vitamin B2 can be found naturally in many plant-based feedstuffs such as grains and oilseed meals (Ruiz and Harms, 1988; Ruiz and Harms, 1989; Banaszkiewicz, 2011). Merrill et al. (1981) stated that a large portion of riboflavin in feed materials exists in the form of free coenzymes - flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) - mostly FAD. Its liberation from these is aided by gut pyrophosphatases and phosphatases (Chung and Baker, 1990), a necessary step for absorption. Due to variability in the content and bioavailability of vitamin B2 in plant-derived ingredients, supplementation of fermentation-synthesized riboflavin becomes indispensable (Chung and Baker, 1990; Dove and Cook, 2000; Sheraz et al., 2014; Witten, 2018; Kleyn and Chrystal, 2020). This form of riboflavin can be directly absorbed, but liberation from the feed matrix is still necessary (Hynd, 2019). Afterwards, solubilization allows for
absorption, which is then facilitated by transport proteins (White and Merrill, 1988). The riboflavin transporters such as riboflavin-binding protein (RBP) take up the vitamin from the intestine and serum (M’Clelland, 1996). RBPs ensure the safe transfer of vitamin B2 to different tissues (Miller et al., 1982; Mac Lachlan et al., 1994; Loch et al., 2018). Studies indicate that riboflavin is mostly absorbed in the proximal small intestine (McCormick, 2012).
Cellular uptake of riboflavin is enabled by riboflavin transporters, which are situated on cell membranes and require calcium ion-dependent RBP receptors to activate endocytosis (Combs and McClung, 2017; Kirchhausen et al., 2014). This process results in the internalization and release of vitamin B2, followed by the recycling of the receptor and RBP (Combs and McClung, 2017). Riboflavin is found in higher concentrations in tissues with a high energy demand, such as muscle and liver, as well as in tissues with ample redox reactions like the heart and kidney (Carlsson and Sherman, 1938; Hodson, 1940; Leonhardt and Wenk, 1997; EFSA, 2006; McCormick, 2012). Excess vitamin B2 is excreted through urine, although some metabolites are produced through oxidative cleavage and conversion of the ring methyl functions (McCormick, 2014). Finally, the synthesis of FMN and FAD from riboflavin is done with riboflavin kinase, riboflavin 5'-phosphate (i.e., FMN), and FAD synthetase (Karthikeyan et al., 2003; Pinto and Zempleni, 2016; Fischer and Bacher, 2010; Combs and McClung, 2017; Poudel et al., 2022). These derivatives interact with the electron transport chain and various dehydrogenase reactions (Friedmann, 1974).
“The Growth-promoting Vitamin”
In the first half of the 20th century, riboflavin was referred to as “growth-promoting vitamin G” due to its role in growth and development (Norris et al., 1930; Lepkovsky and Jukes, 1936; Norris et al., 1936; Bethke et al., 1937; Heuser et al., 1938; Bethke and Record, 1942). Its influence on poultry growth stems from its involvement in a multitude of physiological processes, such as nutrient utilization, protein synthesis, and enzyme activity (Bethke et al., 1937; Ashoori and Saedisomeolia, 2014; Biagi et al., 2020; Leiber et al., 2022). Vitamin B2 facilitates metabolic pathways responsible for the degradation of carbohydrates, lipids, and proteins, leading to enhanced nutrient breakdown and absorption (Northrop-Clewes and Thurnham, 2012; Suwannasom et al., 2020; Cogburn et al., 2018). This is integral in the growth of living organisms, as it induces energy production, furnishes foundational constituents, and upholds redox equilibrium (De Oliveira et al., 2008). Riboflavin, through FAD and FADH2, engages in redox reactions that contribute to energy synthesis and streamlined growth processes (Van Every and Schmidt, 2021). Dysfunction in this cycle or disruptions in FAD/FADH2 participation can impede growth-associated pathways and cellular functionality.
The importance of riboflavin in protein synthesis for poultry growth is critical. Vitamin B2 is involved in the folding of proteins in the endoplasmic reticulum with the help of an enzyme called endoplasmic reticulum oxidoreductase 1 (Tu et al., 2000; Zhang et al., 2022). Hypovitaminosis B2 can inhibit the process due to a lack of flavoproteins and an imbalanced redox state, leading to a stress response (Zhang et al., 2022). Research has also indicated that a deficiency of vitamin B2 substantially reduces glutathione reductase activity and glutathione levels, and downregulates the expression of endoplasmic reticulum oxidoreductase 1 and protein disulfide isomerase (Taniguchi and Nakamura, 1975; Manthey et al., 2005; Xin et al., 2017; Cogburn et al., 2018; Tang et al., 2019). Evidence for the impact of riboflavin on poultry growth abounds, with experiments conducted across various species that have explored the effects of vitamin B2 supplementation on growth performance (Norris et al., 1930; Lepkovsky and Jukes, 1936; Norris et al., 1936; Bethke et
al., 1937; Heuser et al., 1938; Asplin, 1941; Bethke and Record, 1942; Chou et al., 1971; Jortner et al., 1987; Johnson and Storts, 1988; Olkowski and Classen, 1998; Cai et al., 2006; Lambertz et al., 2020; Brooks and Martin, 2023). In broiler chickens, riboflavin supplementation has been associated with increased growth rates, improved feed conversion efficiency, and increased carcass yield (Ruiz and Harms, 1988; Roth-Maier and Kirchgeßner, 1997; Lambertz et al., 2021). Riboflavin also contributes to proper feather and skin development, with inadequate levels linked to conditions like “clubbed down syndrome” or the twisting of feather follicles, as well as dermatitis (Lepkovsky et al., 1938; Jukes et al., 1947; Coles and Cumber, 1955; Haves and Buss, 1965; Cogburn et al., 2018). Investigations in turkey poults, ducks, and chickens have all demonstrated that dietary supplementation of vitamin B2 positively impacts growth and development (Patrick et al., 1944; Ruiz and Harms, 1989; Thesing et al., 2021). A summary of the impact of riboflavin supplementation on poultry performance can be found in Table 2.
Table 2. Impact of riboflavin supplementation on the performance and leg abnormalities of poultry
Poultry species
Broiler chicken
Broiler chicken
Turkey poults
Dietary supplemental riboflavin levels in feed
0.0, 0.9, 2.0, 2.8, 3.6, 4.4 mg/kg
2.75, 2.78, 3.05, 3.40, 3.71 mg/kg
0.0, 0.6, 1.1, 1.7, 3.1, 4.4 mg/kg
Effects of riboflavin supplementation on performance and leg abnormalities
Improved body weight, feed intake, FCR and reduced occurance of leg paralysis
Improved body weight, feed intake, FCR and reduced occurance of curled-toe paralysis
Improved body weight, feed intake, FCR and reduced occurance of leg paralysis
Broiler chicken
1.7, 3.7, 11.7 mg/kg
Broiler chicken 1.0-5.0 mg/kg
Broiler chicken 4.0-10.4 mg/kg
Pekin ducks 0.0 and 10.0 mg/kg
Broiler chicken
Broiler chicken
0.0, 1.0, 2.0, 3.0, 4.0, 8.0 mg/kg
0.0, 0.2, 0.5, 0.9, 4.5 mg/kg
Broiler chicken 0.0, 9.0 mg/kg
Bobwhite quail
0.0, 0.8, 1.5, 2.5, 3.5, 5.0 mg/kg
Bilateral leg weakness and rotation of the metatarsus with flexion of the digits and hock lesions in “the 1.7 mg/kg group” as well as leg weakness in “the 3.7 mg/kg group” compaed to the “11.7 mg/kg group”.
Improved body weight and FCR
Reference
Ruiz and Harms (1988)
Chou et al. (1971)
Ruiz and Harms (1989)
Johnson and Storts (1988)
Olkowski and Classen (1998)
Improved daily weight gain, FCR and European broiler index1 Lambertz et al. (2021)
Lower mortality, improved average daily gain, feed intake and gain/feed ratio
Lower mortality, improved body weight, feed intake, FCR and reduced occurance of leg paralysis
Lower mortality, improved body weight and reduced occurance of leg paralysis
Improved weight gain and FCR and reduced occurance of leg paralysis
Tang et al. (2017)
Roth-Maier and Kirchgessner (1997)
Wyatt et al. (1973)
Summers et al. (1984)
Lower mortality, improved body weight and FCR Serafin (1974)
Ringnecked pheasants
Broiler chicken
Laying hen
0.0, 0.4, 0.9, 1.3, 1.8, 2.4 mg/kg
Improved weight gain and reduced occurance of leg abnormalities
0.8, 6.6, 20.0 mg/kg Improved FCR
0.0 and 2.9 mg/kg
Improved egg weight
Broiler breeders 2.5 and 4.0 mg/kg No effect
Broiler chicken 2.5 and 4.0 mg/kg
Turkey poults
Laying hen
0.0, 2.0, 4.0 or 8.0 mg/kg
1.55, 2.20, 4.40, and 8.80 mg/kg
Scott et al. (1959)
Poudel et al. (2022)
Naber and Squires (1993)
Leiber et al. (2022)
Improved growth rate and feed consumption Leiber et al. (2022)
Higher body weight Lee (1982)
Improved egg production and egg weight
Squires and Naber (1993)
1 European broiler index= daily weight gain (g) x survival rate (%)/feed conversion (kg feed/kg body weight gain) x 10.
Oxidative Stress Defense
Oxidative stress, a result of an imbalance in reactive oxygen species (ROS) production and cellular detoxification mechanisms, is a major challenge to poultry health and productivity (Shastak et al., 2023). Riboflavin is a central component of the defense system against this threat (Zhang et al., 2020). Recent research has revealed riboflavin’s powerful indirect antioxidant properties (Ashoori and Saedisomeolia, 2014), highlighting its importance in ROS neutralization and cellular protection (Cogburn et al., 2018).
Avian cells generate ROS as natural byproducts, and an excessive accumulation of these can cause damage to lipids, proteins, and nucleic acids, leading to disrupted vital functions, weakened immunity, and a range of poultry ailments (Forrester et al., 2018; Shastak et al., 2023). This is where riboflavin’s role as an antioxidant is significant. It participates in several enzymatic reactions, mainly within the mitochondria’s electron transport chain (Cogburn et al., 2018; Balasubramaniam et al., 2020), and is a precursor for two coenzymes, FMN and FAD, which activate crucial antioxidant enzymes to maintain cellular redox balance (Lee, 1982; Donaldson, 1986; Deyhim et al., 1992; Ashoori and Saedisomeolia, 2014). Riboflavin is also involved in the glutathione redox cycle, which helps protect against ROS damage (Suwannasom et al., 2020; Figure 1).
Lipid-peroxide/ H2O2
Glutathione peroxidase
Lipid-OH H2O
Glutathione reductase
Figure 1. Conversion of oxidized glutathione (GSSG) to the reduced form (GSH) by glutathione reductase requires riboflavin in the flavin adenine dinucleotide (FAD) co-enzyme form for its activity (Suwannasom et al., 2020). G-6P-D=glucose-6-phosphate dehydrogenase.
Zhang et al. (2020) conducted a study to see the effect of varying dietary riboflavin levels (0-15 mg/kg) on the antioxidant capacity of White Pekin duck breeders. It was found that those with no vitamin B2 supplementation showed higher plasma malondialdehyde levels and decreased glutathione levels, supporting riboflavin’s vital role in oxidative defense. Furthermore, in vitro experiments have also demonstrated riboflavin’s ability to react with organic radicals and superoxide anions, forming leuko forms which can be further oxidized (Stepuro et al., 2002).
Modern techniques of poultry production expose avian species to an assortment of stress-inducing factors, such as higher temperatures, pathogenic microorganisms, and environmental pollutants, contributing to an increase in oxidative stress conditions (Mishra and Jha, 2019; Shastak et al., 2023). Furthermore, the deliberate genetic selection aimed at promoting accelerated growth rates and heightened egg production can also lead to an increased production of ROS (Surai et al., 2019). This emphasizes the importance of riboflavin and other antioxidant vitamins like retinol, αtocopherol, L-ascorbic acid, and calciferol. Through dietary supplementation, riboflavin can strengthen antioxidant defense mechanisms, improve overall health and performance (Lee, 1982; Donaldson, 1986; Deyhim et al., 1992; Zhang et al., 2020), and even boost immune responses (Alamin et al., 2009; Figure 2), leading to better economic outcomes (Lambertz et al., 2020; Leiber et al., 2022; Cai et al., 2023).
Figure 2. Riboflavin is converted by riboflavin kinase into flavin monophosphate (FMN) and flavin adenine dinucleotide (FAD), which is essential cofactor of the phagocytic NADPH oxidase 2 (Nox2) to generate reactive oxygen species (ROS). Riboflavin deficiency renders the phagocyte Nox2 incapable of producing ROS, a process crucial for deactivating phagocytosed microbes and regulating the inflammatory response in innate immune cells. TNF=tumor necrosis factor; TNFR1=tumor necrosis factor receptor 1 (Suwannasom et al., 2020).
Reproductive Efficiency and Hatchability
A key factor that has been under close examination regarding the parameters of reproductive performance and hatchability in the poultry industry is riboflavin. Much attention has been given to the influence of vitamin B2 on egg production, egg quality, and hatchability by both researchers and poultry farmers (Davis et al., 1938; Lepkovsky et al., 1938; Schumacher and Heuser, 1939; Naber and Squires, 1993; Squires and Naber, 1993; Abrams et al., 1995; Cogburn et al., 2018; Tang et al., 2019; Zhang et al., 2020). Studies have confirmed that a deficiency of riboflavin can have a
significant negative impact on the success of poultry reproduction, carrying immense economic and bird welfare implications.
The role of riboflavin in sustaining optimal egg production rates has been extensively explored (Daviss et al., 1938; Naber and Squires, 1993; Cogburn et al., 2018). Its participation in energy metabolism and cellular activity is directly related to the energy-demanding process of egg production (Zhang et al., 2020). Moreover, the antioxidant properties of vitamin B2 are also essential in shielding the embryo from oxidative stress (Loetscher et al., 2014; Yigit et al., 2014; Cogburn et al., 2018; Tang et al., 2019).
The mechanisms by which riboflavin deficiency can affect reproductive success are complex and involve several physiological processes. One possible mechanism is linked to riboflavin’s role in energy metabolism, with its deficiency potentially leading to a metabolic crisis (Cogburn et al., 2018). Without an adequate amount of riboflavin, energy production will be affected, hindering the high-energy requirements of reproductive processes such as follicle development, egg formation, ovulation, and embryo development and viability (Davis et al., 1938; Vieira, 2007; Scanes and Christensen, 2020). Hatchability is mainly affected by riboflavin deficiency, followed by a decrease in egg production (McDowell, 2000). Furthermore, research has demonstrated a direct correlation between the amount of riboflavin in the hen’s diet and the vigor and viability of the baby chick (Anonymous, 1969). The effects of vitamin B2 supplementation on poultry reproductive performance and hatchability are summarized in Table 3.
Table 3. Impact of riboflavin supplementation on poultry reproductive performance and hatchability
Poultry species Dietary supplemental riboflavin levels in feed
Laying hen
Laying hen
0.0 and 2.9 mg/kg
1.55, 2.20, 4.40, and 8.80 mg/kg
Duck breeder 0.0 and 10.0 mg/kg
Duck breeder 0.0 and 16.5 mg/kg
Effects of riboflavin supplementation on reproductive performance and hatchability Reference
Improved hatchability
Improved egg production, egg weight, hatchability, and hen weight as well as reduced incidence of hemorrhagic embryos and clubbed down
Improved hatchability
Improved hatchability and embryo weight
Broiler breeders 2.5 and 4.0 mg/kg No effect
Duck breeder 0, 2.5, 5, 10, and 15 mg/kg
Laying hen 0.9-8.1 mg/kg
White leghorn and Rhode island red breeder hens 1.0 and 2.5 mg/kg
Improved hatchability
Improved egg production and hatchability
Reduced embryo mortality and number of malpositioned embryos
Riboflavin Requirements for Poultry
Naber and Squires (1993)
Squires and Naber (1993)
Tang et al. (2019)
Zhang et al. (2021)
Leiber et al. (2022)
Zhang et al. (2020)
Onwudike and Adegbola (1984)
Leeson et al. (1979)
The nutritional requirements for vitamin B2 vary amongst different poultry species and at different stages of their life cycle, due to the complexity of avian growth and development. For example, broilers during their fattening phase require increased riboflavin intake for muscle and skeletal development (Olkowski and Classen, 1998; Ribeiro et al., 2020). Conversely, laying hens have distinct needs during their peak egg production phase (Naber and Squires, 1993; Zhang et al., 2020). Turkeys, with their unique growth characteristics and reproductive patterns, have slightly different riboflavin requirements than both meat-type and laying-type chickens (Table 4).
Additionally, the absorption and utilization of riboflavin is affected by the quality of the feed (Lambertz et al., 2020; Chung and Baker, 1990). Stressful conditions, such as environmental, physiological, or pathogenic, can also increase the need for riboflavin, as it aids in the preservation of cellular integrity (Poudel et al., 2021). Sources like the National Academies of Sciences, Engineering, and Medicine, the Gesellschaft für Ernährungsphysiologie (GfE), and recommendations from poultry breeding companies, like Aviagen, Cobb-Vantress, and Lohmann, are often consulted by poultry producers in order to determine the right balance of scientific knowledge and the genetic potential of their flocks. However, there is a need to update the NASEM requirement estimates, as the last revision dates back to 1994 and there have been genetic advancements in broilers, turkeys, and laying hens. In commercial farming scenarios, stress, infections, and illnesses may require higher vitamin levels than the NASEM requirement estimates (Leeson and Summers, 2001; Shastak and Pelletier, 2023). Vitamin B2 is essential for energy metabolism and tissue repair, and its role in antioxidant defense systems becomes increasingly vital under stressful conditions (Van Every and Schmidt, 2021).
For skeletal development, the mineralization process is dependent on riboflavin-supported metabolic pathways (Motyl et al., 2017). Hypovitaminosis B2 can cause an increase in deformed legs and poor mobility in broilers (Summers et al., 1984). Riboflavin is also vitally important for citrate accumulation, which is necessary for bone stability, strength, and resistance to fracture (Costello et al., 2012)
Common feed ingredients can contribute to riboflavin content, but these levels are often insufficient to meet poultry requirements (Roth-Maier and Kirchgessner, 1997; Olkowski and Classen, 1998; Witten and Aulrich, 2019; Brooks and Martin, 2023). Thus, premixes used in poultry feeding are universally supplemented with vitamin B2 and other vitamins. Quality control in premix and feed production is essential, as well as the selection of feed ingredients that ensure optimal riboflavin provision.
Table 4. Vitamin B2 guidelines for poultry: Requirement estimates (NASEM), allowances (GfE), and recommendations (remaining sources)
(Hybrid turkeys) 2016
1Valid for Ross, Arbor Acres, and Indian River broilers breeds as well as Nicholas and B.U.T. medium and heavy turkey lines; 2valid for Lohmann, Hy-Line, and H&N Nick layer breeds; 3valid for ISA, Dekalb, Shaver, Bovans, Babcock and Hisex layer breeds. 4at 100 g of feed per hen daily; n/a=not applicable.
Conclusions
1. Riboflavin plays a crucial role in poultry nutrition and health, serving as a coenzyme in various metabolic reactions, particularly in redox reactions and energy metabolism, emphasizing its indispensability in avian physiology.
2. Vitamin B2 significantly contributes to enhancing nutrient utilization, facilitating protein synthesis and folding, and promoting enzyme activity, collectively supporting optimal growth and performance in domestic fowl.
3. Riboflavin’s impact on reproductive parameters, such as egg production, egg quality, and hatchability, is significant, influencing the reproductive success of avian species and having far-reaching implications for economic viability and animal welfare considerations.
4. In essence, vitamin B2 emerges as a pivotal micronutrient within the intricate web of poultry nutrition, exerting profound effects on growth, health, and reproductive performance. As the poultry industry continues to advance, a deeper understanding of riboflavin’s roles and innovative approaches to its supplementation will prove essential in sustaining and furthering this vital sector.
Recommendations
Formulate poultry diets to meet riboflavin requirements for optimal growth and well-being. Recommendations for optimal vitamin B2 supply by respective breeding companies can be considered as a reference.
Consider higher vitamin B2 supplementation during periods of stress or disease risk.
Optimizing riboflavin’s supply as the growth promoting vitamin could contribute to enhancing animal performance and welfare.
This article is based on the publication: Shastak Y, Pelletier W. From Metabolism to Vitality: Uncovering Riboflavin’s Importance in Poultry Nutrition. Animals. 2023; 13(22):3554. https://doi.org/10.3390/ani13223554
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