In this technical guide developed by Nuproxa, we explore lesser-discussed aspects of choline chloride usage in animal nutrition, as well as its direct impact on productive performance and metabolic efficiency in animals. 

What exactly is choline?

Choline, chemically known as 2-hydroxyethyltrimethylammonium, is a colorless quaternary ammonium salt, highly soluble in water and alcohol (Sigma-Aldrich, 2001; Farina et al., 2014).

While some researchers have traditionally classified choline as a B-complex vitamin, it does not meet all classical criteria for this group. Unlike other vitamins, it does not function as a coenzyme, its requirements are significantly higher (in grams, not micrograms), and it does not fit the standard definition of a vitamin: an essential compound synthesized endogenously and acting as an enzymatic cofactor (McDowell, 1989).

Functionally, choline plays crucial structural and metabolic roles: it participates in the formation of membrane phospholipids (e.g., phosphatidylcholine), in synaptic transmission through acetylcholine, in the export of hepatic lipids, and in methylation processes via its conversion to betaine (Zeisel & Blusztajn, 1994; EFSA, 2011).

Although many animals can synthesize sufficient amounts of choline under maintenance conditions, this capacity is often insufficient under high production demands, such as in rapidly growing poultry and swine with high reproductive efficiency. In these cases, dietary supplementation becomes essential (NRC, 1987; EFSA FEEDAP, 2011).

Forms of choline in food and their bioavailability

Choline is foundin multiple chemical forms in food, such as phosphatidylcholine and free choline, which directly influences its absorption, metabolism, and bioavailability. According to Zeisel et al. (2003), these forms include:

• Free choline
• Glycerophosphocholine
• Phosphocholine
• Phosphatidylcholine
• Sphingomyelin

These can also be classified by solubility (Zeisel, 2006):

• Lipid-soluble: phosphatidylcholine (the main dietary form) and sphingomyelin
• Water-soluble: free choline, phosphocholine, and glycerophosphocholine

This structural diversity complicates quantitative analysis, as some lab methods do not effectively extract or detect all choline forms. Furthermore, not all forms are absorbed or metabolized equally, making nutritional evaluation more complex.

A study by Cheng et al. (1996) in rats found significant differences in the distribution of radiolabelled choline esters in tissues like the gastrointestinal tract and liver, indicating variation in bioavailability depending on the ester form.

A brief history of choline in animal nutrition

Choline was first identified in 1847 by Gobley, who discovered it in egg yolk in the form of phosphatidylcholine—coining the term “lecithin.” Later, Strecker isolated choline from pig bile in 1849, followed by von Babo and Hirschbrunn who extracted it from white mustard seeds in 1852 (McDowell, 2000).

Its nutritional importance in animals became clear in the mid-20th century. In 1940, Jukes demonstrated that a choline-deficient diet caused growth retardation and perosis in poultry—a condition marked by swollen metatarsal joints, hemorrhages, skin discoloration, and leg deformities (Titus, 1932).

Choline deficiencies were later documented in hamsters, calves, rabbits, and guinea pigs, and its preventive role in piglet leg weakness syndrome was confirmed (McDowell, 2000).

Quillin et al. (1961) also revealed an inverse relationship between dietary choline and methionine in broiler diets: lower choline levels required higher methionine supplementation to maintain weight gain. This is likely due to their shared function as methyl donors.

Subsequent studies (Derilo & Balnave, 1980; Miles et al., 1983; Pourreza & Smith, 1988) suggest that higher choline levels may also increase the requirement for sulfur-containing amino acids, demonstrating a complex metabolic interaction.

Key functions of choline in animal nutrition

Choline’s functions can be categorized into two main groups:

1. Metabolic precursor function

Choline is a precursor to several essential compounds:

• Sphingomyelin: structural component of cell membranes, especially in the myelin sheath surrounding nerve axons
• Acetylcholine: crucial neurotransmitter in nerve signal transmission
• Phosphatidylcholine: major membrane phospholipid, critical for cell integrity
• Betaine: important methyl donor in methionine synthesis and homocysteine regulation

These roles underscore choline’s importance in neurological, hepatic, lipid, and epigenetic functions.

2. Indirect regulatory function

Through its role in phosphatidylcholine synthesis, choline indirectly regulates:

• Energy metabolism, enhancing nutrient utilization
• Lipid export from the liver, helping prevent hepatic fat accumulation (steatosis)
• Fat digestion and absorption, through bile and lipoprotein production

Current choline requirements in production animals

Despite its importance, most official choline requirement references for livestock are based on older studies from the 1980s–1990s, when animals had lower growth rates and feed efficiency, limiting their relevance for modern genetics.

Broiler chicken requirements

According to the NRC (1994):

• 1,300 mg/kg from 1 to 21 days of age
• 1,000 mg/kg up to 6 weeks of age

Recent work by Lima (2012) estimated choline requirements between 1,013 and 1,232 mg/kg during the starter phase of broilers.

Importantly, these values account for both naturally occurring choline in ingredients and dietary supplementation, making them practical references for modern nutritionists.

Choline content and sources in common poultry feed ingredients

Despite Choline concentration in feed ingredients varies widely, depending on their origin, composition, and lipid content. Table 1 (adapted from Farina et al., 2014) provides an estimate of choline levels in commonly used poultry feed ingredients. It’s important to note that analytical discrepancies exist due to chemical diversity, processing, and lab techniques.

Table 1. Estimated choline content of common ingredients in poultry nutrition (adapted from Farina et al., 2014)

Animal-derived ingredients, particularly those rich in phospholipids such as offal, egg yolk, and fatty tissues, are typically higher in choline compared to plant-based sources (Engel, 1943).

Kettunen et al. (2001) demonstrated that in poultry meat, most choline is found in fatty tissue, primarily as phosphatidylcholine, reinforcing the link between lipid content and choline availability.

Offal vs. muscle
Offal (e.g., liver, heart, kidneys) contains more choline than skeletal muscle, which shows little variability across mammalian species (Engel, 1943). This information is valuable for both commercial formulations and functional feed strategies.

A comparison of choline content in different animal and plant-based foods is presented in Table 2, adapted from Glade et al. (2019) and Wiedeman et al. (2018).

Table 2. Estimated choline content of common ingredients in poultry nutrition (adapted from Farina et al., 2014)

Practical use of choline chloride as a nutritional supplement

Choline chloride (CC) is a widely used synthetic additive in animal nutrition, manufactured from chloroethanol and trimethylamine (TMA), using ethylene oxide as a catalyst. By-products like residual TMA and ethylene glycol must be carefully controlled to ensure product safety and quality.

In general, animal feeds are rich sources of choline, and its concentration is related to the phospholipid content (Engel, 1943). For example, Kettunen et al. (2001) demonstrated that most of the choline is associated with the adipose tissue of chicken meat, i.e., associated with phosphatidylcholine.

Issues related to trimethylamine (TMA) content

TMA residues are often listed in choline chloride certificates of analysis. Feed manufacturers generally accept levels below 300 ppm, as higher concentrations are linked to the compound’s fishy odor and potential toxicity.

Moreover, TMA can also be formed in the gut via microbial fermentation of unabsorbed choline, further increasing animal exposure. Studies show that up to two-thirds of supplemented choline chloride may be lost as TMA before absorption—compromising efficacy and increasing toxicological risk.

These issues present technical and health-related challenges when formulating choline sources for high-efficiency production systems.

Coming next…

In the second part of this article, we will explore other critical issues related to choline chloride use, including:

• Risks of excessive dietary chloride
• Vitamin losses in premixes
• Hygroscopicity and processing challenges
• Potential adulteration of commercial CC sources

Stay tuned! This information can help you make safer and more efficient decisions in animal nutrition management. Don’t miss it!

Bibliography

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