Discuss the metabolism and physio-nutritional role of biotin and choline with particular reference to growing animals.

Biotin: Metabolism and Physio-Nutritional Role

Biotin is a water-soluble vitamin that functions as a cofactor for carboxylase enzymes involved in several metabolic pathways. Its metabolic journey is intricate:

• Absorption: Biotin is absorbed in the small intestine via a sodium-dependent multivitamin transporter (SMVT).
• Metabolism: Once absorbed, biotin is converted to biotin-5'-phosphate (B5P), the active coenzyme form. This conversion requires ATP and biotinidase.
• Carboxylation Reactions: B5P acts as a cofactor for four major carboxylase enzymes: acetyl-CoA carboxylase (ACC), pyruvate carboxylase (PC), propionyl-CoA carboxylase (PCC), and 3-methylglutaconyl-CoA carboxylase (MGC). These enzymes are vital for fatty acid synthesis (ACC), gluconeogenesis (PC), catabolism of odd-chain fatty acids and branched-chain amino acids (PCC), and cholesterol biosynthesis (MGC).

Physio-Nutritional Role:

• Growth and Development: Biotin is essential for normal growth and development, especially in rapidly growing animals.
• Skin and Coat Health: It contributes to healthy skin and coat, preventing dermatitis and alopecia.
• Hoof Health: Crucial for maintaining strong hooves in livestock, preventing lameness.
• Glucose Metabolism: Involved in gluconeogenesis, contributing to blood glucose regulation.

Choline: Metabolism and Physio-Nutritional Role

Choline, unlike a true vitamin, is a conditionally essential nutrient, meaning animals can synthesize it but often require dietary supplementation, especially during periods of high demand. Its metabolic pathway is as follows:

• Absorption: Choline is absorbed in the small intestine via both active and passive transport mechanisms.
• Conversion to Betaine: Absorbed choline can be converted to betaine, which serves as a methyl group donor in various metabolic reactions.
• Phosphatidylcholine Synthesis: A significant portion of choline is used for phosphatidylcholine (PC) synthesis, a major phospholipid in cell membranes. PC is also a precursor to acetylcholine.
• Acetylcholine Synthesis: Choline is crucial for acetylcholine synthesis, a neurotransmitter vital for nerve impulse transmission.

Physio-Nutritional Role:

• Cell Membrane Integrity: PC is a critical component of cell membranes, maintaining their structure and function.
• Neurotransmitter Synthesis: Essential for acetylcholine production, impacting muscle contraction, memory, and cognitive function.
• Lipid Transport: Betaine, derived from choline, aids in lipid transport and reduces hepatic fat accumulation.
• Methyl Group Donor: Involved in homocysteine metabolism, preventing hyperhomocysteinemia.

Combined Role in Growing Animals

Growing animals have increased demands for both biotin and choline due to their rapid growth and development. Biotin supports the synthesis of structural proteins and fatty acids necessary for tissue growth, while choline contributes to cell membrane formation and neurotransmitter synthesis crucial for neurological development and efficient nutrient utilization. Deficiency in either nutrient can significantly impair growth, skeletal development, and overall health. For example, a deficiency in biotin in young pigs can lead to stunted growth, dermatitis, and neurological problems. Similarly, choline deficiency in poultry can result in perosis (splayed legs) and fatty liver syndrome. The ratio of these nutrients in the diet must be carefully considered to ensure optimal utilization.

Deficiencies & Consequences

Nutrient	Deficiency Symptoms in Growing Animals
Biotin	Stunted growth, dermatitis, alopecia, neurological signs, poor hoof health (especially in ruminants), decreased milk production.
Choline	Perosis (splayed legs) in poultry, fatty liver syndrome, neurological dysfunction, impaired growth, reduced reproductive performance.

The 2020 FAO feed additive guidelines emphasize the importance of supplementing diets with biotin and choline, particularly for intensively reared livestock.

Case Study: Biotin Deficiency in Dairy Cows A study in Wisconsin (2015) found that biotin deficiency in dairy cows led to poor hoof health, resulting in lameness and reduced milk yield. Supplementation with biotin improved hoof horn quality and decreased the incidence of lameness. Q: Can animals synthesize biotin? A: While some bacteria in the gut can synthesize biotin, the amount produced is often insufficient to meet the animal’s requirements, especially in growing animals. National Dairy Development Scheme (NDDS): This scheme, launched in 2017, aims to improve the productivity and competitiveness of the Indian dairy sector, indirectly promoting the use of essential nutrients like biotin and choline for optimal animal health and milk production. Carboxylation: A chemical reaction that involves the addition of a carboxyl group (-COOH) to a molecule, catalyzed by biotin-dependent carboxylase enzymes. Global Biotin Market: The global biotin market was valued at USD 270 million in 2022 and is projected to reach USD 380 million by 2028, reflecting increasing demand in animal feed applications. (Source: Grand View Research, 2023) Phosphatidylcholine (PC): A phospholipid comprising choline, phosphate, and fatty acids; a major structural component of cell membranes and a precursor to acetylcholine. Poultry Industry: The poultry industry frequently supplements feed with choline chloride to prevent perosis, a common skeletal deformity. Choline Requirement in Pigs: The NRC recommends a choline requirement of 250 mg/kg in growing pigs, which increases to 400 mg/kg for piglets. (NRC, 2011)