What is magnesium oxide?
Feed-grade magnesium oxide is made by heating (calcining) natural magnesite (magnesium carbonate), which drives off carbon dioxide. Türkiye is one of the important magnesite-producing countries. The calcination temperature largely decides the product's character: lightly calcined (caustic) magnesia is porous and chemically reactive, while hard-burned and dead-burned magnesia, made at higher temperatures for refractories, is much less reactive and less suitable as a nutritional source.
Natural magnesite contains some calcium, iron and silica, so commercial feed-grade MgO contains less magnesium than the theoretical 60.3%. The value on the certificate of analysis is used in formulation.
What does magnesium do in animal feed?
Magnesium is needed for bone, for the activity of many enzymes, energy metabolism, and nerve and muscle function. It also plays a role in calcium metabolism, including the hormonal response that mobilises calcium around calving.
- Ruminants: magnesium is absorbed mainly from the rumen, and the animal has little readily mobilisable magnesium reserve, so a regular daily supply is important.
- Grass tetany (hypomagnesaemia): grazing cattle and sheep on lush spring or autumn pasture, which is often high in potassium and nitrogen and low in magnesium, are at risk; magnesium supplementation in mineral feeds, licks or concentrates is a standard preventive measure.
- Dairy cows: MgO is used as an alkalising buffer, often together with sodium bicarbonate, and to meet the magnesium requirement in transition and lactation diets.
- Pigs and poultry: magnesium needs are usually largely met by feed ingredients; MgO can be used in premixes when a supplement is required.
How is the magnesium requirement assessed?
Requirements depend on species, production level and diet, and are given in nutrient requirement tables. In ruminants, the absorption of magnesium is reduced by high dietary potassium, so the diet's potassium level, the source of magnesium and the season are considered together. To convert, divide the magnesium target by the Mg content of the product: for example, supplying 10 g of Mg with an MgO declaring 54% Mg requires about 18.5 g of product. Excess magnesium can reduce palatability and loosen faeces.
Quality criteria for feed-grade magnesium oxide
Two MgO products with the same declared magnesium content can perform differently, because availability depends on how the material was made.
- MgO / Mg content: declared and confirmed by analysis for every lot.
- Reactivity: measured by tests such as the citric acid reactivity test or acid-neutralising tests; more reactive material is generally considered more available, while dead-burned material performs poorly.
- Particle size: finer particles dissolve faster, but very fine material is dusty and can be less palatable; the grade is chosen to suit the application.
- Impurities and heavy metals: calcium, iron and silica as purity indicators; lead, cadmium, arsenic and mercury within feed legislation limits.
- Moisture and storage: MgO slowly picks up moisture and carbon dioxide from the air, so it is stored dry in closed bags.
- Traceability: a certificate of analysis (CoA) and lot number for every batch.
Practical points
MgO has a bitter taste, so in free-choice mineral licks it is often combined with palatable ingredients such as molasses. In premixes it is alkaline and can affect the stability of some sensitive vitamins, which is considered when designing the premix and its storage life. Other magnesium sources, such as magnesium sulphate, chloride or phosphate, are sometimes used where a more soluble source is needed. Local regulations and the product label always prevail.
CTF Premix and magnesium oxide
Magnesium oxide can be included in CTF Premix's mineral, vitamin-mineral and custom premixes according to the customer's formulation, for example in ruminant mineral premixes. Premixes are produced at our 10,000 m² facility in Ankara under ISO 9001:2015 and GMP with lot traceability, and each lot's certificate of analysis can be viewed on the batch verification page.
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.