What is glycine?
Glycine is the smallest of the 20 amino acids in proteins: its side chain is a single hydrogen atom, so unlike the others it has no L- and D-forms. It is abundant in collagen and other structural proteins.
Animals can synthesise glycine, mainly from serine and also from threonine and other precursors, so it is traditionally classed as non-essential. Because glycine and serine are readily converted into each other, nutritionists often evaluate them together as glycine plus serine, or as a glycine equivalent.
Why do birds need so much glycine?
Poultry excrete nitrogen as uric acid rather than urea, and every molecule of uric acid incorporates one molecule of glycine. Nitrogen excretion therefore uses up glycine continuously. In addition, glycine is needed for the synthesis of creatine, glutathione and haem. In young, fast-growing broilers the combined demand can exceed what the bird synthesises, which is why glycine is described as conditionally essential in this species.
What does it do in animal feed?
- Low-protein broiler diets: when crude protein is reduced and the classic limiting amino acids are supplied in crystalline form, glycine plus serine is often one of the factors that limit further reduction.
- Growth and feed efficiency: an adequate glycine supply supports weight gain and feed conversion in such diets.
- Interaction with threonine: threonine can be converted to glycine, so a generous threonine supply can partly cover glycine needs and vice versa; the two are considered together.
- Pigs: glycine is generally not a limiting amino acid in practical pig diets, although its role in very low-protein diets is studied.
Sources and forms
Animal proteins rich in collagen, such as meat and bone meal and poultry by-product meal, are good glycine sources, while vegetable diets based on corn and soybean meal are lower. The need for supplemental glycine is therefore greatest in vegetable-based, reduced-protein broiler diets.
Feed-grade glycine is a white crystalline powder, usually produced by chemical synthesis. Its guaranteed content is stated in the product specification and certificate of analysis.
How is the requirement assessed?
Glycine is usually formulated as glycine plus serine or as a glycine equivalent, on a total or digestible basis depending on the system used. The target depends on age, crude protein level and the threonine and choline supply of the diet, because these affect how much glycine the bird can make itself. Supplementation is a formulation decision that should be made by the nutritionist.
Quality criteria
- Guaranteed glycine content and purity.
- Moisture, ash, chloride, heavy metals and microbiological quality.
- Particle size and flowability for even distribution in premixes and feed.
- Certificate of analysis (CoA) and lot traceability.
CTF Premix and glycine
Glycine can be included in CTF Premix's vitamin, mineral and custom premixes according to the customer's formulation, alongside other amino acids, vitamins and trace minerals. Our premixes are produced at our Ankara facility under ISO 9001:2015 and GMP, and every lot is supplied with a certificate of analysis and full lot traceability.
This page is for general information. Inclusion rates and product choice should be decided with a nutritionist, taking into account the species, the feed formulation and the applicable regulations.